Hacker News Reader

Comment by shotta | Hacker News Reader

One of my friends had to buy a new (to him) car out of necessity. He decided to buy the only new car on the lot. He was bragging. Great deal.

Here’s the catch.. it requires premium. He didn’t know that. The dealer made sure not to volunteer any extra info. He’s keeping those miles low.

View on HN

I like how you say "the dealer made sure not to volunteer any extra info" as if this was a secret and the dealer somehow scammed your friend into buying a brand new car at the height of a chip shortage and record high car prices.

The lifetime difference of premium gas financially is next to nothing.

The car requires premium gasoline?

Is that a thing?

edit: Thanks for the info. Did not know that. I've always had piece of shit cars that could probably run on McDonald's french fry oil. :)

Yup, some engine's are designed for it. Usually for performance reasons if the engine is boosted or high compression.

Some engines require higher octane gasoline, yes. You can use lower octane in it, but you're going to hurt the engine.

It’s been a thing. My car is 20 years old and requires it. Engines with higher compression require higher octane fuel to reduce pre-detonation and pinging. Using low-octane fuel in one of them can cause game-ending physical damage to the engine.

Many more modern cars can sense lower-octane fuel and adjust for it, at the cost of power and efficiency (i.e., mileage).

Yes, I have a car which requires premium gasoline. Though I haven't tried putting in regular, my understanding is that doing so would induce knocking.

A car with knock sensor will detect lower-quality fuel and pull back timing. This will usually limit your power, but not damage your car. My car manual even explicitly states that it won't affect engine lifetime.

Full disclosure, I still use premium anyway because I want to keep the car for a long time and I don't fully believe this disclaimer.

Generally you'll get worse fuel economy due to the ECU and knock sensor detecting the lower grade fuel and pulling ignition timing out. It's unlikely you'd even save money at the pump

The octane rating you see on gas indicates the pressure at which gasoline will combust. Engines tuned to a higher compression to ignite require higher octane level gasoline. Using something other than what the engine is tuned to might put a lot of extra wear or degrade performance of the engine.

The gasoline will ignite before it is supposed to, forcing the piston back down before it has travelled all the way to the top of it's stroke. The engine will destroy itself. You can hear "knocking" coming from the engine when this is happening. It's worse than it sounds.

I know this is definitely true of older engines that aren't controlled by fancy software, but I suspect at least many consumer cars are capable of adjusting to the difference. I could be wildly wrong here though, and wouldn't want to test it myself.

Knock sensors are standard on every car made by a global automaker since the early 90s when fuel injection became universal

Some vehicles, especially ones with OEM performance tuning, run high compression ratios or forced induction. Higher octane gas allows for more compression within the piston before ignition. I had a 2003 Toyota Matrix that redlined at 9100 rpm and used their fancy Toyota variant of VTEC that would dynamically swap the camshafts on the engines past a certain RPM. Although the engine was naturally aspirated (no turbo), it had the compression ratio of 11.5:1, which is pretty high for an economy vehicle (1.8L)

All the comments are giving unequivocal yes’s, I’ll note that some cars (my buddy’s Subaru) will say they require premium but work just fine without. Currently going 240k miles still strong.

In case you're being facetious, old Mercedes diesel cars can literally run in old MacDonalds french fry oil with a tiny bit of modification.

Reply on news.ycombinator.com