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Comment by roflchoppa | Hacker News Reader

Coolant sure, my RSX has a radiator leak for the past 2 years.

Oil not so much.

I had a friend who had a Honda (edit: actually, Toyota iirc) for ~15 years that didn’t know it had oil; So when they sold it and was asked how often the oil was changed, the potential buyer was met with a quizzical look. Tires and gasoline and window washer fluid was its maintenance.

I coworker of my mother some 20-25 years ago bought a new car. Drove it until it stopped and refused to go further. Called some road service who upon inspecting it announced that she had run out of gas. She was surprised, "Cars still need to be refueled??!!".

I find that a bit hard to believe. Someone in that family knew and took care of it sometimes.

The longest I've seen a used car go without an oil change was 40k miles and it was changed when it started making noise instantly on startup. That was basically 90k to 130k. Sure 0 to 40k would go a bit better.. but not 15 years of typical driving.

Between carbon blowby, gasoline dilution, oil burning at the rings/cylinder walls even if minimal, no car is making it 15 years if the person drives more than 5k miles a year IMO.

I wouldn't believe it either unless I heard it directly from my earnest friend who learned at that moment:

1) cars have oil

2) said oil should be changed regularly

Unless they were driving very very low miles per year, they are simply incorrect. A car isn't making it over 100k miles without an oil change IMO, even a Toyota.

Similar to how this person went most of a lifetime without noticing and wondering what oil change businesses, advertisements, coupons, etc were for... They also didn't notice someone in their household or a service provider of some kind (brakes, tires, idk) changing their oil.

Just pour coolant in via the oil cap. It'll be fine. /s

On older heavy equipment of low value and high difficulty servicing (think like a forklift or skid steer) it's not uncommon to replace the coolant with oil to mitigate a head gasket issue and simply drain some oil and add to the coolant on some semblance of a schedule.

One of my favorite tractors was the old Oil Pull's which were designed for oil in the radiator. (they were a gas engine, but designed to run on "tractor fuel" which is closer to diesel than gasoline - in order to work the engine had to be very hot)

It's of course possible to design engines to be oil cooled, though water-glycol tends to be preferred due to about twice the specific heat capacity, meaning smaller coolant channels, radiators, and fans are required.

I don't think it occurred to anyone in 1905 that a water/glycol mix might be good. They either used straight water with a warning to drain the engine when you shut down in cold weather so it didn't freeze, or they used oil. My 1939 tractor has instructions to start the engine and then pour water in the radiator when it is below freezing.

Not in 1905, no. I believe water-glycol mixes became widely used in the 1920'ies. But without glycol, water is an even better heat transfer agent. Shame about the freezing thing, though.

Is it specific heat that we care about, or rate of heat transfer? Specific heat matters a bit, but if you make your coolant take twice the energy to change 1 degree, the same thing happens on the radiator side and you must release twice the heat to cool 1 degree.

Rate of heat transfer in general if probably more important.

Well, it gets really complex. Yes, specific heat matters, but as you say so does the heat transfer coefficient. And the viscosity. And is the flow laminar or turbulent? Etc.

There are various figures of merit, such as the Mouromtseff number https://doi.org/10.1109/JRPROC.1942.234654 or https://www.electronics-cooling.com/2006/05/comparing-heat-t... for a quick overview.

Some tables of heat transfer coefficients: https://www.engineersedge.com/heat_transfer/convective_heat_...

But, turns out water is just very very good also when you take these other factors into account. Compared to oil, it has, as mentioned, much higher specific heat, it has higher heat conductivity, it has lower viscosity which means less pumping power and more likely to see turbulent flow which helps with mixing.

In the case of the oil pull tractor they needed to run the tractor much hotter than water boils - even if they had known modern antifreeze it still boils too hot. They also didn't know to make modern radiators - they usee very large radiators to make up for lack of surface area. (They also used exhaust to pull air through the radiator instead of a fan). All in all a very ingenious design - but there is good reason they don't make them like that anymore. (My 1939 is a lot more modern - and it lacks electric start)

I gotta hit VTEC I need oil :)

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