Oil Change, Hot or Cold?

racesport · March 29, 2005

I have a friend who runs an import repair shop. He has a mechanic who does not want to change oil hot. What is GM's point of view on oil changes, hot or cold or just change it please?

04-silver · March 29, 2005

I no expert but I would say hot, cold oil doesn't seem to drain very well.

My .02 is that he is tired of getting burnt by a hot engine..........

Edit- sorry didn't realize this was in the ask the GM expert

John

GM-Tech · March 29, 2005

I have a friend who runs an import repair shop. He has a mechanic who does not want to change oil hot. What is GM's point of view on oil changes, hot or cold or just change it please?

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GM has no view on this that I've ever seen. Common sense would say that an engine that is hot and just been shut off would probably have more of any solid contaminants in suspension and they will then go out with the oil. If it's been sitting and cold, I would think some would settle out. However, this is probably pretty insignificant.

I can't blame the guy for not wanting to get scorched when pulling the drain plug or filter. Personally, I like to drain my oil after the engine is warmed up.

jhm · March 31, 2005

The oil should be warm, not hot. If the engine is at operating temp and you drain all the oil out you could risk piston damage. Come to think of it my Ariens snowblower manual says something to this effect, warm not hot as

GM-Tech · March 31, 2005

If the engine is at operating temp and you drain all the oil out you could risk piston damage.

Please explain the basis of this theory.

MrQuadrasteer · March 31, 2005

My .02:

If the engine is cold, having sat 4+ hours- DO NOT start and warm it up. The oil has settled in that time, if you start it you'll have more oil left behind in the passages.

If it's warm or hot... don't get burned !!

I end-up changing my oils hot 99% of the time...

jhm · March 31, 2005

If the engine is at operating temp and you drain all the oil out you could risk piston damage.

Please explain the basis of this theory.

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Expansion of metal due to high temperature with no oil circulating to act as a heat sink. This is my theory. I really do not see any gain in dumping full operating temp oil, I would rather be safe and dump it when it is warm. Does your shop drain customers oil at operating temp? Probably the engine has been shut off for possibly hours, then they drive it onto the lift and drain the oil.

mcreyaufmiller · March 31, 2005

So by your theory, if I shut my engine off, I could risk piston damage because there is no oil flowing to act as a heat sink?

GM-Tech · March 31, 2005

Expansion of metal due to high temperature with no oil circulating to act as a heat sink. This is my theory.

When the engine is shut off, as it would be if you were about to drain the oil, how is the oil circulating?

jhm · April 1, 2005

Expansion of metal due to high temperature with no oil circulating to act as a heat sink. This is my theory.

When the engine is shut off, as it would be if you were about to drain the oil, how is the oil circulating?

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Of course it is not circulating. Each time you shut your engine down you dont immediately drain all the oil out of it. The oil in the engine is absorbing heat, so if your engine is at say 210 degrees with the oil in it and you park and drain the oil out, IN MY OPINION you could POSSIBLY cause damage to pistons, rings, etc. I know a small engine like the 8.5 hp Tecumseh on my snow blower is not the same technology as our Vortecs, but the owners manual actually says "do not drain oil while engine is hot, drain only when warm". Again as I initially said, this is my theory, I am not saying I have proof damage will be done.

GM-Tech · April 1, 2005

Again as I initially said, this is my theory, I am not saying I have proof damage will be done.

Understood. Look at it this way. Whether the engine is running or not, most of the oil is in the pan. The oil level in the pan is never up to a point where ithe pistons or cylinder walls are emersed in it, dissipating heat. That doesn't change whether you leave the oil in the pan or drain it out. Doesn't matter if the engine is hot, cold or in-between. Any heat dissipation of the cylinder walls or pistons by oil that is simply in the oil pan is insignificant if there is any at all.

I couldn't say why Tecumseh suggests what they do.

racesport · April 1, 2005

I suspect the reason Tecumseh says not to drain hot is due to liability. Remember McDonalds and the woman and the hot coffee?!

An air cooled engine probably runs hotter than our water cooled trucks. I am sure they do not want home owners suing for burns by following directions.

Just a guess in our litigous society.

snoman · April 4, 2005

I suspect the reason Tecumseh says not to drain hot is due to liability. Remember McDonalds and the woman and the hot coffee?!

An air cooled engine probably runs hotter than our water cooled trucks. I am sure they do not want home owners suing for burns by following directions.

Just a guess in our litigous society.

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In a air cooled engine oil provides more cooling than in a water cooled engine and the oil can get scorching hot! I have a JD 318 lawn tractors that if you change it hot after mowing the oil is just about "steaming" when you drain it out. I have changed oil hot for 35 years hot though and my theory is that it runs out quicker and likely to hold more particals in suspension than in a cold engine that has set. There is more than enough oil left on pistons after a hot drain to lube them when it starts up so no cause for concern there.