Why warm the oil

Ok, I know this is a dumb question, I always do it, but just wondered why (so please don't hate to much):

Why do you need to warm the car before changing the oil?

the viscosity becomes lower when warm and allows the oil to run out faster and more completely

I've always considered it a good idea in order to get any contaminants into suspension, and get the oil to flow easily so as to remove as much of the old oil as possible.

02Pilot wrote: I've always considered it a good idea in order to get any contaminants into suspension, and get the oil to flow easily so as to remove as much of the old oil as possible.

That's why I do it...gets all the gunk up in suspension and it flows better and more quickly to get a more complete oil change.

A million years ago, back when I worked on jets, this was discussed in the jet engine school. Supposedly, it was studied and shown that heating and mixing the oil in the hot engine got contaminants stirred up, and better able to flow. This got more of them out and allowed the fresh oil to start off less contaminated.

Don't really know if it's true, but it sounds good.

Hmmmmmmmmm........ I heard that you were supposed to do it when it was cold!

That way more oil is in the pan and not up in the head where it won't have time to drain out from.

Also, I thought the point of variable weight oils (5W30) was cold viscosity then warm viscosity.. and the cold viscosity was lower so that it would flow better when the engine was cold..

Do I have it backwards?

I always end up doing mine warm anyway because I'm always driving my car...

I usually drain my oil over the course of a couple of hours. The last thing I do before draining it is run out and get some more.. then with thick gloves so I do not burn myself, I pull the plug and let is drain for an hour or so while I work on other things.

I always do mine warm for the reasons listed above, plus it makes getting the oil filter off a lot easier-less chance of the seal sticking.

I once heard of a guy who started the car up to get all of the oil out of the engine Needless to say, not a good idea ;)

I think FT and O2Pilot have it there as for "conventional wisdom." That's what I've always heard, anyway. I, personally, don't worry about it and change the oil when I have the car ready to be serviced. It that's after I've just driven it or after it's been sitting a week, I change it out either way. That means the Esprit is usually cold, the Rolla usually hot, the Camry either way, the bikes usually cold, etc.

Multiweight oils, like 5W30, mean that it flows like a 5W when it is cold and a 30W when it is hot. They still will flow much better at hot temps.

Speaking of oil, I just bought a Genuine billet APC oil cap for Toyotas at the dollar store. It doesn't say 710 on it, but I'm thinking of adding that. I couldn't pass up a deal like that.

I warm it up because my topsider oil sucker won't suck very well when it's cold, especially for those wintertime changes here in Rochester.

Because it takes me 10 minutes to line up the ramps and a few hundred miles off the clutch to get it up the ramps on the third or fourth try.

Multiweight oils, like 5W30, mean that it flows like a 5W when it is cold and a 30W when it is hot. They still will flow much better at hot temps.

Although with old oil, I believe this ability dissipates and the oil becomes more of a single weight. In which case, heating should help more with old oil.

I change it when it's convenient, but I definitely don't bother warming it up if it isn't warmed up already. Some think it helps to stir the sludge up so you'll get more of it out, personally I think that is offset by the amount of oil that stays up in the engine. When your engine is cold it's had time to get as much oil as possible down in the sump, while you'll miss a bunch that hasn't drained down to the bottom when it's warm. In reality, it doesn't make much of a difference, the important thing is regular oil changes. :)

Bryce

I always go out of my way to heat it up. The time it takes between switching the car off and actually draining the oil should be enough to let it settle to the bottom...I'm pretty sure it all drains out because it usually takes a while to fish out the drain plug and break loose the oil filter (which is always inexplicably 50x tighter than when it went on), which is done while the oil is still free to drain. The oil's barely dripping out at that point, if it's dripping at all.

GameboyRMH wrote: I always go out of my way to heat it up. The time it takes between switching the car off and actually draining the oil should be enough to let it settle to the bottom...I'm pretty sure it all drains out because it usually takes a while to fish out the drain plug and break loose the oil filter (which is always inexplicably 50x tighter than when it went on), which is done while the oil is still free to drain. The oil's barely dripping out at that point, if it's dripping at all.

Gameboy, have you ever torn an engine down on an engine stand? Once you pull the oil pan, it will continue to drip, seemingly forever! Don't ever assume it's done dripping, the moment you pull your drip pan out from under it is when it will start dripping again.

Bryce

I always do it so that every time I touch the oil pan, I burn m hand. And so that when I finally get the damned drain loose, the oil comes out super-fast and burns my hand causing me to drop the red hot plug into the scalding hot oil. And so that I burn my unprotectable wrists on the hot@$$ intake manifold when I try to squeeze my arm down the little gap to grab the oil filter.

Oh yeah. It also helps with all that stuff mentioned above.

Nashco wrote:

GameboyRMH wrote: I always go out of my way to heat it up. The time it takes between switching the car off and actually draining the oil should be enough to let it settle to the bottom...I'm pretty sure it all drains out because it usually takes a while to fish out the drain plug and break loose the oil filter (which is always inexplicably 50x tighter than when it went on), which is done while the oil is still free to drain. The oil's barely dripping out at that point, if it's dripping at all.

Gameboy, have you ever torn an engine down on an engine stand? Once you pull the oil pan, it will continue to drip, seemingly forever! Don't ever assume it's done dripping, the moment you pull your drip pan out from under it is when it will start dripping again. Bryce

I know there's always little pools of oil in all the nooks and crannies, oil will leak until it's either cleaned out or coagulated with dust and dirt into a coal-like substance...but my point is that the oil is as thoroughly drained as it can be by simply removing the drain plug.

I always do it when the engine is reasonably cool just so I don't burn myself like Confuzion3 up there.

I used to bump the engine once most of the oil drained out, so more would come out of the crank passages, but that's just a bit too anal.

I do allow over 15 minutes for draining though.

Jack