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Comment by CoffeePython | Hacker News Reader

I worked as a maintenance technician at a gas station for 6 years before I switched into software engineering.

Some interesting things about gas dispensers/pumps:

- What most people call a gas pump is a dispenser. The actual pump is submersed inside the underground gas tank.

- mid grade gas is just premium and regular gas that is gets mixed at the dispenser before the fuel is dispensed.

- Holding the hose up high and pulling the trigger does not allow more fuel to drain from the hose after reaching your prepaid amount

- people drive off with the nozzle still in their car surprisingly often. There is a magnetic breakaway so the hose will disconnect and not pull the dispenser over.

I can probably think of some more of people are interested

View on HN

I worked as a cashier in my family's gas station for a few years. I ended up doing contract development work for a retail petroleum distributor about 15 years later.

A couple of these that I can think of:

- The temperatures in our underground storage tanks were very stable, varying only by a couple of degrees F irrespective of the air temperature.

- Fuel almost always arrives warmer than the underground temperature, so you see contraction of volume on your tank monitor as newly-dropped fuel cools.

- Gross volume is the amount dispensed into the distributor's transport trucks. Net volume is the amount dropped into the Customer's tank. Gross vs. Net and temperature adjustment factors are a place where distributors play around to eke out some margin. I wrote some code that took into account air temperature at the terminal (the "rack") where trucks were filled, along with historical rack temperatures, to produce temperature-adjusted normalized costs. When you're making fractions of a cent per gallon margin every little bit helps.

Adding to this, at least the station I worked at used the tank temperature to adjust for density changes. You were buying 1L at 20C, so in the middle of winter when the fuel was 10C, you'd get a slightly smaller volume since the density increased. And slightly more volume during summer.

So uhhh, I guess I should insulate my home natural gas pipe at the outdoor above-ground portion before it hits the meter?

(The gas would be warmer coming from the ground than atmospheric temperature during the heating season)

Wait: wouldn’t I want it to be cooler when it’s measured so it’s denser and I get more moles per volume measured?

Natural gas measurement is temperature-compensated, at least here in central europe. You pay for the heat energy contained in the gas, not for the net volume. The compensated heat energy is calculated based on consumption profile of the consumer class (cooking only, cooking and heating, business etc) and temperature profile of the location (pretty fine grained temperature regions).

But yes, you can still trick the meter by cooling the input medium.

One thing that threw me off in Europe is that apartments will still have individually metered water and natural gas (probably paying more in monthly account fees than usage...).

Like a cold water tap, I guess the temperature of the gas can really warm up in the pipes when it isn't run enough to get 'fresh' cold water/gas from underground quickly.

At where I live, trading water is forbidden. We rent appartments and we must not have any profit on the water. Usually, the consumption is separated per person, but sometimes that is not possible (when there are stores, for instance).

For an odd reason, however, flat rate is acceptable, so you can charge tenants a fixed monthly fee and make an actual profit out of it. Sure, there's a risk you set the flat rate price wrong.

Yeah, theoretically that would work (cooling the gas before it hits your meter). The effect would be far larger than for gasoline. Based on the ideal gas law, dropping the temperate by 20C would reduce the volume by 7% while keeping the mass of gas the same! The change in density of gasoline is only ~2% over the same temperature range.[2]

However, you'd need to warm the gas back up before burning it as furnaces are typically tuned for a specific density of gas.

[1]https://www.omnicalculator.com/physics/ideal-gas-law [2]https://www.ic.gc.ca/eic/site/mc-mc.nsf/eng/lm00129.html

Time for me to get my meter out of the sun. And shovel snow on it in winter. But I suppose the biggest gains would be during summer where the gas dwells a bit as it draws intermittently.

It would be interesting to see how much the gas temperature varies. Pipes are usually below the frost line, so pretty much the same temperature year round.

You’re right that if your meter is in the sun and it gets warm that probably warms the gas somewhat. How much, I’d be curious to know.

And I also have no idea if gas companies adjust for it at all. I assume not since most meters are pretty basic.

I think they just adjust globally. Either by adding a factor that depends on average temperatures, or a surcharge to account for 'system loss' between their central meter and the sum of all consumer meters.

GasCo doesn't care if individual customers pay the correct amount, just that they get their costs covered in aggregate.

I feel like natural gas is so cheap that any effort is worth at most $5, for a huge house with lots of people. My total bill in the summer is only $10.

Might be worth shoveling snow on in the winter.

refrigerated meter?

I've also heard you could probably do something with magnets near your electric meter.

(I read this from some "get even with someone" book where it said to prominently put magnets on the target's electric meter for the utility guy to find)

Magnet is very well known trick for workers, so you’ll get fined for that. Besides, it only worked with old meters.

I've always thought fuel should be sold by mass, not volume (tank LPG often is).

My first job I worked doing software for petrol pumps and underground tank monitoring systems.

One of the main guys who worked on the pump software, in forth, actually wrote a book where the petrol pump is his main example https://www.manning.com/books/functional-reactive-programmin...

> people drive off with the nozzle still in their car surprisingly often

I did this in the late 80s. The handle ripped off and was not magnetically attached. However, gas did not spill from the hose.

I drove back to the station and handed it to the attendant sheepishly. He said thanks.

The breakaways on the dispensers I worked with in the early 90's had shear pins and were mechanical. We lost 1 or 2 a year at our station in rural Ohio.

I’m happy to report that this may be fixed going forward. Tesla and I think most EV’s will not let you in drive while plugged in.

Funny story, I broke a plug while undoing it (there was some jank), and it refused to let me go faster than ~5mph. I needed the service station to remove the adapter.

That sounds like a dangerous design flaw. What does “some jank” mean?

I fear any car that can refuse to let me drive. There's no way they couldn't trigger that remotely in an individualized way.

Any vehicle with Onstar has this as an intentional feature. The feature was introduced in 2009.

Electronic ignition interlocks have been common on most vehicles over the past 20 years too... the only reason you can't remotely prevent most other cars from starting is simply software.

https://www.toyota.com/connected-services/remoteconnect/

https://owner.ford.com/fordpass/fordpass-sync-connect.html

https://www.nissanusa.com/connect/features-apps.html

https://www.hyundaiusa.com/us/en/blue-link

etc...

Since all the hardware exists, all you have to do is find an exploit: https://www.wired.com/2015/07/hackers-remotely-kill-jeep-hig...

Thanks for helping raise awareness about these too. It’s a scary world out there when the devices people rely on can work against them on the whim of another.

Imagine a $5000 ransom popping up in your HUD or your car will automatically drive off a bridge.

Doors and windows are locked and you have 120 seconds.

As long as it is not brake by wire you are fine for ransoms if you are stationary.

I am quite scared of internet connected cars that can steer the wheel automatically though. That is madness.

Thats not a good plan - most people wont be able to transfer $5000 in 120 seconds just because it is not sitting in the cureen t account tied to your card.

It will use hacked Equifax credit reports to generate an amount that you are most likely to have with 95% confidence.

Secondly, Tesla owners tend to be more affluent. Imagine a cyberpunk world where ransomware attacks are a fact of life: buy cheap cars with reasonable security and minimise your total cost of ownership. Heh.

you can do small installments and make it seem normal

You choose "PAY", put in your bank account PIN, the car drives off the bridge anyway and the virus erases itself from the car.

It would be much better for future business to have stories circulating from people who were safe after paying the ransom.

It is very likely that whatever you are driving today, if it was manufactured in the past two decades in Europe, North America, Brazil, Korea, or Japan, will not let you shift into Drive (automatic) without depressing the brake pedal.

And there's also universally an override to that interlock and the manual tells you exactly where it is. Usually you just pop off a little cover on the gear shift and depress a mechanical button under that cover with the key to the car or any thin enough piece of metal long enough to reach. If Tesla doesn't have something equivalent for charging cables that can be used by the owner then that's a flaw with Tesla. There's a reason why everyone else has an override.

Closes the market to external power banks. Perhaps add a bit to detect the type of power supply.

I drove off with nozzle once because it was my first time filling my new German car, which has the port on the right, which I wasn't used to.

Thanks is an amazing response to this

How far did you get from the station before you realized it and turned back?

Not the OP but the cashier at the Wendy’s drive-through pointed it out to the driver when I was a passenger. I think the passengers laughter could be measured in litre of tears.

About 1/2 a kilometer. I stopped the car, removed the handle, and drove back to the gas station.

The attendant had been outside, so he saw it happen. In fact he had pumped the gas (this was not self-serve).

And when I came back, holding the nozzle in my hand, he was dumbfounded.

In the UK, you can't "latch" it on - for flow, you need to hold the handle down constantly. This means that you are unlikely to drive off with the dispenser still in the car as there is no benefit to the driver to leave it in when they have finished.

It is interesting that it is the same dispenser design used around the world, but the latch is removed in the UK.

However, As a teenager I discovered the wonders of the latch on fuel dispensers on airfields. Then on the road I started using the removable fuel-cap as a wedge to the dispenser. eeeeek!

(Now I use an electric car)

Interesting. Similarly in some countries the ATM will return the money first and then the card and in other countries the order is reversed.

Yeees. I used to work for Diebold on ATM's, and we had some research that proved that:

  - people want to take out money from the machine
  - once they have their money, the activity is complete

We found that if we provided the card back before the money, they stopped leaving their card in the machine. This is because the 'activity' was taking out money.

When chip-enabled cards and ATMs first started making their way to the general public in the U.S. I had a friend who forgot his card 4 times in a single month, the last 3 times just hours after receiving a replacement in the mail. Each time he admitted that once he had the cash, he completely forgot about the card. I'm not sure if the machines beeped back then or not, but for his sake I'm glad this particular UX was adjusted.

You're not the only one - though I completely forgot I used to do that until I read your comment!

No latch in Finland either.

Same in Australia—no latch.

Except some independents still have the latch which means you can fill and wash your windows at the same time.

How often do people have gasoline fights?

Works RadioShack many many years ago.

Customer came in soaked in gasoline.

Into an electronic store...

She got very fast service as we rushed to get her out the door.

Apparently there was an “incident” at the pump.

We suspected lack of brains

Problem exists between cognizance and cranium.

(Anyone have a good word starting with K?)

I think Zoolander ended this practice from becoming common.

Early candidate for most important documentary of the 21st century

Only on the way to get an orange mocha frappuccino.

Haha thank you for this.

> Holding the hose up high and pulling the trigger does not allow more fuel to drain from the hose after reaching your prepaid amount

Doesn't it though? I feel like I know this because if I don't do it, gas pours out onto the side of my car and/or the ground, when I pull the hose out.

It doesn't push any more out past the meter but it certainly clears the last few cc from the line.

I was once told by an electrical engineer that the whole ban on using a cell phone near a pump was due to potential interference with how the dispenser tracks how much you have pumped.

Is there any truth this?

The situation is a bit complicated. From having done a moderate amount of research over years, there are basically two answers:

1) Signs that you should not use a cell phone at a gas pump are largely a result of a string of incidents in the '90s in which gas station fires occurred when the operator was using a cell phone. Causation was assumed and the warning decals were put on pumps. Later research by the Petroleum Energy Institute, an industry group, did not find any incidents that were actually caused by cell phones. The correlation may be due to a confounding factor, that people talking on cell phones are more likely to get in/out of their vehicle while pumping which could cause a static discharge. The PEI reports that, in general, improvements in vapor management in vehicles and fuel dispensers makes the risk of static discharge causing a fire low at modern gas stations.

2) General industrial best practice, and various safety regulations which are influential but not necessarily applicable to consumer gas stations, prohibit the use of electronic devices near flammable substances unless those devices are certified to be safe for that use. While many cell phones are probably "intrinsically safe" (do not involve potentials high enough to reasonably produce a spark), few are actually verified to that standard by the manufacturer (would need to be labelled "intrinsically safe" by the manufacturer following their safety analysis). In a safety-regulated environment they would thus be prohibited out of an excess of caution.

On the balance it seems likely that cell phone use at the fuel dispenser is probably not a hazard, but it never hurts to minimize distractions and extra factors when handling something potentially explosive.

Furthermore the cost is low: 60 seconds of not using your phone isn’t a big deal. If you’re calling someone, put them on hold.

I once had a stopover on a flight and was told that I was not allowed to use my phone in the plane as they where currently refueling. I am still skeptical if my phone would really be able to cause some hazard.

This might have been true historically, but samsung has since released the Galaxy Note 7.

They seem pretty capable of exploding in your pocket and starting a fire at the petrol station. No need to be talking on it at the time.

Once in a blue moon even a dog shoots his owner, or a person is born with two genitals.

I don’t think that’s the main concern. I worked on offshore platforms and the devices needed to be class 1 div 2 compliant. Meaning they need to be sealed completely to avoid vapors being sparked by electrical devices. It’s a small risk, but gasoline vapor is very combustible.

I wouldn't be surprised it was to discourage distractions while fuelling up.

You know, for the types that tend to drive off with the dispenser nozzle still in the tank.

What I read back when the bans were lifted around here was that cell phone use correlated with people opening the car door and rummaging around, which created a static electricity buildup, and that that was the real fire risk.

You’re supposed to ground yourself by touching your vehicles before the gas pump

Source: workplace safety videos I was forced to watch, years ago

I'm not sure vehicles on rubber tires are particularly well grounded.

Normal tires have carbon added to the rubber to make them slightly conductive, enough to drain static.

Specialty tires like you find on drag cars do not. This is why you also see grounding straps dangling from drag cars -- to keep the driver from getting a shock when they step out after a run.

"grounding" in this case refers to equalising the potential difference.

You are.

These days the filler tube on the car is made of plastic so it's less important. I did get yelled at for not putting a (plastic) fuel container on the ground "to ground it" before filling it, so the rituals persist even when the root cause has been resolved.

Absolutely, yeah, you’re supposed to! People don’t, though, hence the (still small) fire risk.

As if anybody is going to remember that.

Gas pumps where I live have a piece of metal you can touch to ground yourself

When you fill in an.airplane, you need to ground it with a special cable that comes with the pump.

Was water in the fuel ever a thing?

I had a car run really badly after filling up and had a poke about. I noticed a fluid level in the fuel pipe (it had a glass site bowl thing in the fuel line). It turned out the tank of ‘petrol’ was mostly water.

My father sold gas back in the day. He told me a story of an incident where he accidentally sold water instead of gas. When the supply tanker was filling up the underground reserves, someone forgot to close up the underground reserve. A heavy rain came overnight and water infiltrated the tank.

It was an accident. Repair costs for customers were handled through the gas station's insurance.

Water in the gasoline is an issue in stations that have above ground tanks. When the tanks are mostly empty they’re filled with air, and the changing temperature means water condenses out of the air and ends up in the gas. I used to live in a rural area with a gas station known for watery gas; if we wanted to run a chainsaw we’d get gas from farther away to avoid damage.

Just saw this comment but wanted to respond.

Yes this is a thing and happens semi-often.

Keep in mind I was servicing over 75 locations and each had at least 3 tanks.

The most common way for water to get into the tanks was through the fill ports that the fuel delivery drivers filled the tanks with.

Seals could go bad, or the driver could forget to close a lid 100% of the way. Couple that with high water from rains and you’d typically get a high water alarm.

I think our system was setup to alarm if there were more than 3 or 4 gallons in a tank. These tanks are enormous. I don’t remember the capacity but they had many thousands of gallons of fuel.

Water goes to the bottom of the tank naturally and sets off an alarm. This alarm also stops the pump from running.

We’d call out a vacuum truck to pump the bottom of the tank (usually this cost A LOT of money. $1000 for 15 minutes of work)

Then we’d fix the entry point where water came in. If the alarm cleared on the system, we could turn the pump back on.

Typically the submersible tank pumps pull fuel a few inches off the bottom of the underground storage tank. You'd have to have a very high water-level for the pump to pull water.

People take the possibility very seriously with aircraft, so I inferred that it's a real, but rare, problem.

It's pretty much gone away as a problem for cars, there's been design changes to vehicle fuel tanks, and the use of ethanol as an oxygenate means that water doesn't really build up over time (the ethanol allows the water to mix into the fuel; 'dry gas' is often just a jug of alcohol)

> - people drive off with the nozzle still in their car surprisingly often. There is a magnetic breakaway so the hose will disconnect and not pull the dispenser over.

I've done this at least once that I can remember, and maybe twice or more. Yep, the handle just popped right off. Embarrassing but fortunately not dangerous.

I wonder if this predates any Apple MagSafe patents...

Magnetic kettle leads predate MagSafe by decades as well.

Any truth to the rumor that you should avoid filling your car when the main station tank is getting refilled? Think the logic was that their refilling would stir up sediment and potentially damage your car’s engine.

The fuel flows through a filter in the dispenser, so it shouldn't be problematic.

If you're using a dispenser that's particularly slow it's likely that the filter in the dispenser is clogged, too. At the station where I worked we stopped buying from a distributor who continually delivered "dirty" diesel fuel. Right after we took a load from them we'd see our dispensers flow rates decrease dramatically.

Aren't the fuel filters in cars good enough to prevent engine damage even if foreign objects or residue were to end up in the tank?

Fuel filters should prevent damage to the engine, but if you got a ton of gunk in the filter you might suddenly find yourself with a dead car on the side of the highway because your fuel line is clogged.

How plausible is this scene from Rambo?

https://www.youtube.com/watch?v=MgfoCa2-V3g

Completely plausible with enough movie pyrotechnics.

I worked with a guy that was a SFX guy for the old Walker TV series. Talking about some fun stories. He showed me a few "near misses" where the explosion was "slightly" larger than anticipated, and if you know where/when to look, you see the SFX team running for their lives in footage that made it into the edit. None of the guys I've worked with come close to the Danny McBride character in Tropic Thunder though.

I was filling up one time when the person on the opposite side of the pump drove off with the nozzle still attached. Once the end broke away, the rest of it snapped back and slammed into the other side of the pump enclosure so loudly and violently that it set off my adrenaline and I was freaked out for a good few minutes. Quite an experience!

What fraction of gas sold is mid-grade? I have never purchased it.

Slightly higher compression engines, perhaps <2L high RPM, like sub-compacts or maybe motorcycles. I’ve had rentals, don’t recall. Hyundai?

Some 90s german cars call for mid-grade

Long time ago I read somewhere you shouldn't hold the lever all the way because it could potentially allow more oxygen through and thus have to pay just a little bit more for the same amount of fuel. Is that really true or was I being gaslighted?

The metering is done in the dispenser, not the nozzle.

Yes, but can having the nozzle not 100% open influence the metering?

No, because that would become widely known and people would take advantage of it. I believe they use a https://en.wikipedia.org/wiki/Positive_displacement_meter

I never understand what gas I'm supposed to get with my car. There's 87, 89, and 91 I believe? But I just don't understand why so many choices.

What you are supposed to do is look in the Owner's Manual. It should tell you what octane number gas you should get, plus a lot more. For example, in the manual for mine (a 2006 Honda CR-V) it says this:

===========

Your vehicle is designed to operate on unleaded gasoline with a pump octane number of 87 or higher. Use of a lower octane gasoline can cause a persistent, heavy metallic rapping noise that can lead to engine damage.

We recommend using gasoline containing detergent additives that help prevent fuel system and engine deposits.

In addition, in order to maintain good performance, fuel economy, and emissions control, we strongly recommend, in areas where it is available, the use of gasoline that does NOT contain manganese-based fuel additives such as MMT.

Use of gasoline with these additives may adversely affect performance, and cause the malfunction indicator lamp on your instrument panel to come on. If this happens, contact your authorized dealer for service.

Some gasoline today is blended with oxygenates such as ethanol or MTBE. Your vehicle is designed to operate on oxygenated gasoline containing up to 10 percent ethanol by volume and up to 15 percent MTBE by volume. Do not use gasoline containing methanol.

===========

Dealing with the octane number is easy. Just don't use gas with a lower octane than your manual calls for. You can use a higher octane if you want, but it won't really do anything other than cost more. You'll get the same performance, wear, pollution, and mileage as you would with the octane number given in your manual.

To further clarify, the average street car is designed to run on the ethanol which is sold everywhere, but some engine configurations need a higher octane fuel in order to combust the fuel completely. I had a buddy who rebuilt an engine with a compression ratio that required 91 octane, or he'd get knocking. This was during the late 80's, and more than one station around these parts had pumps selling 95 octane (it might have even been 100) for the real hot-rods.

This whole comment thread is surprising to me because I haven't seen sub-90 octane rating in ages - I have even just checked, and one of the main petrol companies in Poland sells only 95, 98, and special extra variant of 98.

It’s complicated, as that number measures different things in different countries: https://en.wikipedia.org/wiki/Octane_rating#Measurement_meth...

As per usual, the US uses a different scale (AON) than the rest of the world (RON).

USA, they have all that weird stuff there...

> some engine configurations need a higher octane fuel in order to combust the fuel completely

This is incorrect. Higher octane ratings mean a fuel can withstand more compression before detonating. Pre-detonation, or "knocking", where an engine experiences detonation in the cylinder before top dead center can cause severe damage, so higher octane is used with higher compression engines. Lower compression engines see no benefit.

If the fuel pre-ignites, proper flame propagation will be thwarted, and the fuel will not be burned as thoroughly, leaving residue, and exhausting (albeit tiny amounts of) fuel. Sure, I put the cart in front of the horse, but I can always count on HN to point out the pedantic.

Reading this again, you're right, it was a little pedantic. This is one of those topics I feel is just rife with misinformation, so I tend to jump on explanations that don't seem correct at first glance.

I'm sure this is accounted for, but octane levels do degrade if you don't use your car often. So it can be good to put a higher octane fuel in your car.

The instruction manual should say. But in my experience, many (most?) cars have a sticker inside of the door that you flip open to access the gas cap.

Here's a random example I found: https://i.imgur.com/nDkwl0i.jpg

It doesn't actually say "octane", but note that it says "MIN.(R+M)/2", and (R+M)/2 is what you'll see on the pump too, as in this example image: https://img.hmn.com/fit-in/900x506/filters:upscale()/stories...

(This is for the US. I would assume other countries are similar.)

There are different ways of calculating octane and that's why they specify the method.

It seems like in the US, 89, 91 are reasonable octane numbers (from reactions to this post). Around here, I've never seen stuff that low - here, it's Euro95 and Euro98. I've been told a real long time ago that the 95 and 98 in there were octane numbers.

Anyone any idea if octane numbers are calculated differently in US vs EU? Or if someone lied to me? Or if the US is really using much lower-grade petrol than is Conon in the EU?

Yes, they're calculated differently. This covers it pretty well:

https://en.wikipedia.org/wiki/Octane_rating#Measurement_meth...

TLDR, the US and Canada use "(R+M)/2" (also called Anti-Knock Index), and much of the rest of the world uses RON (Research Octane Number).

If you zoom in closely on the first image in my comment above, you can see that the sticker has both. It says "MIN.(R+M)/2 87 Regular" and "MIN.RON 91 Normale".

---

Tangentially, you will see lower-octane fuel in specific parts of the US. Denver, Colorado is nicknamed "the mile-high city" because its elevation is about 1 mile (1.6 km) above sea level. In many parts of the US, you will see octane ratings of around 87, 89, and 93 at the pump, but in Denver you might see 85, 87, and 91. The thinner air reduces the need for high octane.

I suppose something similar must happen in Europe, but it may not be as common or well-known. From what I can tell, non of Europe's large cities are at that high of an elevation.

In my experience in germany, gas is sold as is from the tank, so even at 1200m you'll get Euro95 or Euro98.

They are calculated differently. US numbers are 8-12 lower than EU for the same petrol.

Higher octanes are designed to prevent preignition of the fuel in engines that are supercharged/turbocharged or use higher compression ratios. Preignition is when the fuel combusts before the cylinder is at the "ready" point in its cycle (wherever that is for your car, with variable timing and all that).

As others have said, your manual will tell you, but a good rule of thumb is if you don't have a high performance vehicle or an engine with a turbo or supercharger, 87 should be fine.

Excuse me, but honest question - are there new vehicles sold without compressor?

Yes, though depending on your part of the world there may be more or less. Mazda MX-5 is one example.

Yes. Toyota hybrid engines are not turbocharged, as that's more efficient.

Higher octane means the gas has a better ability to resist knocking, which is spurious ignition not caused by the spark plug. Knocking can damage your engine if it happens often. Turbocharged cars have a higher tendency to knock, so they generally need high-octane gas. If you put low-octane in a turbocharged car, most modern engines will detect the knocking and detune the engine automatically to prevent damage, but that means you're not getting the power or efficiency the car was designed for.

So use high-octane in turbocharged cars and low octane for non-turbocharged cars. (If you use too high an octane in your car, it won't hurt anything but your wallet.)

If you're racing a turbo car you might need close to 100 octane, which cannot easily be bought but it can be made by adding toluene to your gas tank (google it).

Other than that check your owner's manual.

Some states have different levels. In Colorado 85 is common. I assume it has something to do with the air pressure and oxygen content of the air perhaps?

One of the reasons for this is that for a NA (normally aspirated) engine, i.e. not turbo charged or super charged, the lower atmospheric pressure results in a lower compressed pressure (versus sea level) as the piston rises toward the top, which means a lesser chance of pre-mature detonation (knock) due to pressure, which is what higher octane prevents. So therefore you don't need as high octane at higher altitudes.

Unfortunately that isn't true with turbo or super charged engines, which are more and more popular. I really miss the 93 (and even 95) octane fuel I could get in Boston. I use a octane booster in my car here in Colorado to help offset the lower octane pump gas, and allow my turbo charged engine to make more power (by not having to pull timing to accommodate the lower octane gas).

85 is functional at elevation, but definitely still not preferable at elevation.

Works best with carbureted engines, which are obviously few and far between these days. You shouldn't put 85 octane in a modern fuel injected engine period.

The method of fuel metering the car uses does not necessarily have any connection with what octane you should use. It's all about the engine design. If we are going after rules of thumb, I would say that if the car is turbocharged, it will most definitely run better with higher octane. Although my turbo VW can run with regular fuel, it will just change timing and make less power.

I have a 78 Fiat with a carburetor however, that definitely needs 91 or higher.

VW is seemingly, in my experience, an outlier. Their small displacement turbocharged engines will run fine on 87, but really like 91 (or E-15 88). My '14 Jetta with the 1.8T got better power and fuel economy on "the good stuff."

This is an oddly specific hardline stance to have.

When you have 85 octane available at 7,000 ft and your car is engineered to run with 87 at sea level, you'll be fine.

Your car’s manual will say.

> mid grade gas is just premium and regular gas that is gets mixed

There is nothing else "premium" about premium gas, than that it can be compressed more in the engine. Compressibility is measured by the octane rating, so it makes sense than mixing 87 octane gas and 91 octane gas, gives you 89 octane gas (using the American octane scale, Europe uses a different scale).

Depends on your country and gas station. Here in Canada, "premium" fuels often have different additive packages and different amounts of ethanol added. For example, https://www.shell.ca/en_ca/motorists/my-fuels/shell-v-power-...

At what point in the distribution chain is ethanol added? I prefer to run ethanol-free fuel when possible, but would also prefer to use fuel with good detergent additives. I've always wondered if the gas at the local ethanol-free station is missing the additive package as well.

Does anyone still use above-ground tanks? Just wondering if there's any truth to buying gas in bulk during cold weather for density reasons. (though I'd imagine the price/barrel has been fluctuating more than the temperature would cause lately)

There's a station local to me with above ground tanks. They're in an area that flood regularly, which is why the tanks aren't buried.

I've never noticed a measurable difference when filling up the 20 gallon tank in the truck.

I suspect you'd have to buy a LOT to make a meaningful difference.

As I understand it, petroleum companies provide "winter mixes" of fuel that accommodate for the difference in density, so there isn't a real advantage to this.

Summer fuel blends are an emissions control.

https://www.caranddriver.com/news/a15339380/the-vapor-rub-su...

Above-ground tanks can be appreciably cheaper, mostly due to increased inspection and maintenance requirements for underground tanks due to a history of leakage problems. That said, the price difference isn't big enough to justify the use of space (especially considering setback requirements) in urban environments. You will still find above ground tanks in newer gas stations in rural environments, though.

Department of weights and measures calibrate and confirm the amount pumped twice a year. The amount dispensed should be compensated for temperature.

> I can probably think of some more of people are interested

Sure, I'll read a few more.

Yes me too

From what I heard, pretty much all gasoline starts off the same in the US, the brands will add a tiny amount of their own detergent on top of what's already in the base. Seems plausible.

There are many different blends of gas, and refineries change with the weather (winter fuel mix evaporates faster than summer mix, and will not need summer emissions). Gas stations often choose their own mix of detergents/additives, but otherwise all fuel in a town comes from the same refinery with the same contents.

Most stations just go with the refinery default additive mix, which is typically pretty good. Some national brands go with a slightly better additive mix. Some national brands go with a cheaper additive package. You need to be a large chain to afford to pay a chemist to design an additive mix though, so the majority of stations don't.

So if I want at least some of the benefits of the cleaning ingredients in the premium fuel, is the mid-grade an option?

According to https://en.wikipedia.org/wiki/Top_Tier_Detergent_Gasoline you're getting at least the EPA minimum amount of detergent additives even in low-octane fuel, and many brands participate in the Top Tier standard that requires even more additives, again with the requirements applying even to low-octane fuel. So I wouldn't bother paying extra for premium fuel for the sake of additives when the higher octane rating isn't needed. Which gas station you go to will probably affect that more than which grade of fuel you select at the pump.

Although stations buy from a lot of suppliers so how could you even know?

There is generally one refinery that all stations in a given town buy from. Shipping fuel from a different refinery would be enough more expensive that you wouldn't be competitive.

Sometimes stations have their own additive package.

Go to a station that sells one brand. Like a Shell or Exxon (Esso) station.

If you want the cleaning additives you can just buy them separately and pour them in, i.e. Chevron Techron.

You're getting them anyway, but sure in the sense that you're getting part-premium. I don't know many, if any in the US, that have actual USTs full of midgrade and don't blend the two more common ones at the dispenser.

Priming has nothing to do with cleaning. It’s higher octane fuel. If your car Isn’t designed for higher octane fuel it will run like garbage. The whole point of high octane fuel is that it requires a higher temperature to ignite. If your car Isn’t designed for it it’s most likely only going to partially burn the fuel.

No, the main point of high octane fuel is to be resistant to higher compression ratios so it doesn’t pre-detonate. Spark plugs have no issues igniting it.

What op is referring to is additives that are added in by some gas dealers to the high octane fuel to upsell you. “Techron” is one I recall seeing at Chevron IIRC.

You can sometimes buy the additives separately. e.g. for Techron: https://amzn.to/33LH1RN

The parent comment is right. It's not just the spark; heat and pressure are also part of what ignites your air/fuel mixture.

Not with gasoline. A gas engine can ignite at temps well below 0F and low compression.

You might be thinking of diesel. Diesel depends on compression to combust and has heater coils to ensure minimum temps as well.

This is more obvious when you read engine specs and they have minimum octane ratings, not specific ratings.

High-octane fuels will not burn poorly. It just isn't necessary to increase octane further once the threshold of knocking/self-ignition at the target compression and cylinder temperature is reached.

Plus you missed the point: In many places the premium fuel is the same octane number as regular (e.g. 95), but premium is with additives for <insert vague marketing>.

Is sand really efficient? If we overflow, should we put sand ourselves?

According to the story of Douglas Hegdahl it is [1].

[1] https://www.pownetwork.org/bios/h/h135.htm

What does that have to do with sand?

Do you happen to know the ratio of regular to premium in mid grade?

I think it's the same as the relationships between the octane numbers you see. So if the pump as 87, 89, and 91 grades, then the mid-grade will be a 50/50 mix (ratio 1:1) of the 87- and 91-octane fuel. If the grades are, say, 87, 89, and 93; then the ratio would be closer to 2:1 of regular:premium to get to that mid-grade.

Only reason I know this is because premium gas in California used to be 92 octane. So the three choices were 87, 89, and 92. When we dropped to 91 octane, a lot of the stations near me had to swap out the yellow sticker on their mid-grades to read "88.5". That was my clue that the ratio had not been adjusted yet.

> I can probably think of some more of people are interested

Yes please!

Does it make sense to buy premium gas?

Only if your vehicle requires hit. Premium gas is rated for higher compression (generally turbo or supercharged engines). If your owner's manual doesn't recommend a particular octane, just get regular.

With turbos and computer adjustment of timing and everything, it's more plausible than it used to be that premium will give you more power. On the other hand, it's also more likely that a lower grade will not damage your engine even if premium is recommended.

interested!

This is awesome, thank you!

More please :)

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