Changing oil

in the jan 1 “click and clack” article the question of changing oil when the engine is hot or cold is discussed. while i agree with the conclusion that changing when the oil is cold is, i believe there was a little “disinformation” in the article. specifically, no oil will remain coated on the inside walls of the engine since this will have drained down as the engine cools just as effectively as if the oil were changed when the oil is hot. admittedly, there will be a little more left in the pan if the oil is cold but with the current multi-viscosity oils, this will be minimal. had to comment.

Thanks for the comment.

But, I disagree with you. I’ve torn down many engines, and the amount of oil film left on the cylinder walls and bearings is quite decent. Especially the amount of oil left between the rings. The surface tension of the oil helps keep it there, so you’ll have decent protection at start-up until the oil pump can deliver the oil.

Besides, this has been discussed many times on this board. Getting every drop of oil out of the engine is not generally required and fairly impossible to do. Changing it hot or cold means very little, as long as your changing it on a regular basis with a new filter.

But since this is an “oil” post, you will get at least 30 or 40 replies…Tom & Ray post something on this board maybe once a year…

I suppose theoretically one should change the oil when the engine is fully warmed up. However, I’ve changed the oil myself on the Oldsmobile I have owned since 1978. I run the engine just long enough to drive it up on the portable ramps. While the engine isn’t fully warmed up, the parts under the car aren’t as hot, making it safer to do the work. The engine still runs great, but the body has rusted rather badly.

After many years of servicing fleets and seeing vehicles accumulate many hundreds of thousands of miles of reliable service I see no difference in hot and cold oil changes. Some vehicles were always overnight cold and others always end of the day hot when serviced and either way they just kept running and running and running. All makes and models and types of operation from city delivery to 500 mile per day shuttle service to law enforcement/security vehicles.

I don’t think it makes that much of a difference one way or the other. I prefer to do mine when cold or barely warm just to avoid yet more burns and scars. This is especially true of my Lincoln Mark where the oil filter is a bit of PITA to remove.

Cold, hot, or warm, I always allow it to drip for a while before reinstalling the drain plug.

i believe you misunderstood what i said. there should be no difference in the amount of oil left on the engine parts whether you change the oil hot or cold. it will drain down just as much if you change the oil hot or cold. or are you saying it’s better to change it hot because not as much oil will drain down in the time between shutting down and draining?

One has to know that an oil change is not an engine rebuilt. If you really want to clean everything out and have a perfectly clean engine after each “oil change” then you might as well go the rebuild route. Otherwise just exchange to old oil with new and call it a day.

I usually change it with the car warmed up, but after it’s been sitting long enough that the exhaust, etc. has cooled down somewhat. The oil is still hot enough to be uncomfortable, and will burn if you get saturated with it, but not hot enough to cause instant harm. And the exhaust is cool enough that you’ll pull your hand away, but won’t brand you.

Unless you have a filter that mounts upside down, partially fill the filter when installing the new one. You get almost instant oil pressure that way.