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I have always changed the oil in my vehicles with the engine hot, because the manuals always say to let the engine reach normal operating temperature first. Oil change instructions all over the internet say this, too. I've never done it cold because everything says not to, and I never questioned this.

I've burned myself on more than one occasion, last night being the most recent, and it makes it trickier to get the filter out when you have to play Operation on a hot car.

Why do I have to change the oil when the engine is hot and what happens if I do it cold?

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    How are you burning your self? When you remove the drain plug? Try the OTC 5911 it's a magnetic drain plug remover it's 12" and keeps your hand clear of the oil. I don't actually own one of these but I've used one before. When I'm removing drain plugs I just do it by hand and let the plug drop into the pan and pick it up before the oil fills the pan. Have zero issues doing it this way. – Ben Jul 12 '16 at 21:32
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    @Ben Clumsiness. I only ever get burned on the prelude sh, there's not a lot of room to work. Once I dripped oil on my hand, once I bumped the container and splashed it on me, and a few times I got burned on hot parts changing the filter (the filter on the sh is buried deep, I can't even get to it from the bottom, and can barely see it from the top... maybe if I had a few more elbows in my arm lol). – Jason C Jul 12 '16 at 22:32
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    Too hot - consider letting the car cool down to "okay to touch" temp. Inside, the oil will be substantially hotter than the outside, and will still flow okay. If you change the oil cold, it will just take four-times longer to drain out, and is more likely to leave deposits behind instead of sweeping them out. – Criggie Jul 13 '16 at 2:14

11 Answers 11

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The benefits of changing it hot are the that oil is less viscous, so it flows better, allowing more of the old oil to drain. It will also drain more quickly.

I know when I do mine, I let the engine warm up, but not to full operating temperature. Even through latex gloves, full temp oil would burn my hand, and I can do without that. And getting it at least more than warm but not scalding hot, things flow really well. This way you get the best of both worlds, including not burning yourself.

Hope that helps!

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    Personally I use thick latex chemical 1/4 arm gloves. They're a bit wonky to try to unscrew or handle the oil drain plug, but it's really nice to definitely not get burnt and keep clean. I get my bike to full temp and have no issues that way. My opinion is that the few bucks for the gloves made a good impact on time. – kyle_engineer Jul 12 '16 at 23:00
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    With regards to burning ones hands, if you remove the sump plug and it drops into the pan into which you are draining the hot oil, resist the temptation to quickly grab it. Leave it in there until the oil has cooled. Otherwise it hurts quite a bit and you'll not have any hairs on your hand / forearm for weeks afterwards. – Steve Matthews Jul 14 '16 at 12:16
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No problem doing it cold, but better to do it hot so the oil flows easier. Proper tools will help, and so will experience. I've been burned a lot too, but that's because I'm not very adept, and have worked in "quick lube" environments where the customer is in the waiting room after coming off the highway, and I did not have the luxury of any cool-down time.

A shadetree trick that costs nothing, is to run a drywall screw into the bottom of the oil filter. After the pan is completely drained, back out the screw and drain the "reserve" quantity of oil in the filter. This mitigates most of the chance of getting burned during filter removal, and makes the job a whole lot cleaner.

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Think of a cup with sediment (dirt, sand). If you shake it up real good, then dump it out, you will get most everything out. If you let it sit overnight, the dirt and sand settle to the bottom. When you go to dump it out, you dump mostly water, and most of the sediment is still at the bottom of the cup. Your oil is similar with the gunk you are trying to clean out. Allowing it to at least partially heat up lets oil circulate through all the passages and pickup any gunk you want to remove.

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    I'm sorry but your analogy isn't good. We don't drain our oil by turning the car upside town for vacuuming it from the top. We drain it from the bottom so if all the gunk settles on the bottom that isn't a problem unless it is so thick as to prevent it from escaping the drain plug. If oil is this gunky then merely warming up the car won't fix it. @cdunn has the correct answer. – Dean MacGregor Jul 13 '16 at 14:34
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    @DeanMacGregor "We don't drain our oil by turning the car upside down..." Wait, really? I'VE BEEN DOING IT ALL WRONG. – Jason C Jul 13 '16 at 17:06
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    The filter is for gunk. Warming the engine is to decrease the viscosity of oil. – Bevan Jul 20 '16 at 5:36
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When I change oil, I use to run the engine warm enough, but never "untouchable hot". Never to operating temperature, that's what? 180F degrees? I let it get some temperature I can deal with. Then let it drain down all the time it takes. I usually uncap the breather and remove the stick gauge to speed up the process. The oil comes out warm but not enough to burn my hands, say, like hot shower water :)

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Logically, the impurities and any particles heavier than the oil will settle and reside on any horizontal surfaces of the engine that the oil passes through. The majority should settle in the bottom of the oil pan where the oil collects because of gravity. As the oil sits and cools, the majority of sediment will settle in the oil pan along with the oil. This makes it more efficient to quickly drain the majority of the oil even though it is less viscous. However, because the bottom of the oil pan is not shaped like a funnel, much of the oil will simply pass over the heavy sediment as it is drained, though the initial quick flow of the large volume of settled oil may carry a fair amount with it. Think of it like panning for gold and draining the water off the slurry as the gold settles. Therefore, it only seams logical that draining hot oil will carry out more of the sediment that is suspended within it before it has a chance to settle out of the oil. If anyone has a counterpoint to this reasoning please let me know. Thanks to everyone else's viewpoints. I have read them all and appreciate everyone's contributions. PS My honours degree was in Chemistry and Energy & Fuels Science.

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Although not a direct answer to the OP's question, a piece of advice picked up from my many trade customers:

In the new Ford Ranger with 3.2 L Duratorq TDCi ("PUMA" P5AT) diesel engine, draining all the oil out can cause engine failure because the oil pump is not self priming and the oil must be drained and topped in quick succession. No sloping off for a coffee while it drains, you need that bung back in when the flow slows off, so that the oil pump still maintains it's prime. For this reason, doing it cold is better as it keeps the oil viscous enough to hang in the intake for a while.

Quality engineering, boys. Ford have replaced engines themselves because their own technicians took too long / drained too much out!!

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I’ve been contemplating this question for a while (about 40 years) and I know your suggestion of doing it hot/warm is the traditional approach, but as a Mech E and applying some fluids and materials science to it and having done some experiments, I think it’s not correct. Maybe modern mult-viscosity oils are the difference.
When multi-vis oils are heated and moved, they become more viscous - more sticky - making it harder and slower for the oil to drain from the sump and from the higher parts of the engine. Plus, after the engine runs, the oil is spread throughout the engine instead of sitting in the sump and it has to travel further to get to the drain.
I experimented on my 2013 Fusion and found it nearly an hour faster to drain the oil to a point where the oil would slow it’s draining to drip one drop in at least a minute if the oil was cold. IOW, the oil drains faster when cold. This speaks only to the time to get the oil out and assumes that the portion removed from the engine is the same at that point and doesn’t address the question of residue coming with the oil. I will experiment with my 2018 Jeep that takes 0-weight oil over the next year to see if that’s different. For what it’s worth...

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My entire life the only vehicles I have never warmed up before an oil change have been my motorcycles. Currently I drive a 1996 Buick Regal with a 3.8 V6. When I bought it it had 43,000 miles on in 2010. It now has 183,000 miles and is still going strong. I have a 2000 Dodge Dakota pick up with a 4.7 L V8 that has 110000 miles on it that I bought new in 2000. Also a 2012 Ford Focus with over 90,000 miles on it. These are still going strong also. That is my experience thus far on warm vs. Cold oil changes. I am in my fifties and I've been changing my own oil for many years. So that is my two cents worth. I do not agree or disagree with what anyone else has said this is just what I have done for years and it has worked out well for me.

  • It sounds like you change your oil regularly, perhaps often. This habit is far more important than changing it hot vs. cold. – SteveRacer Jul 2 at 1:54
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If you want to get the most oil out of engine change it cold. The engine was hot when you last ran it. The oil ran into the pan until the engine was cold. If you change it hot the oil has not had enough to completely drain. If you warm it up you are simply putting oil back in the top of the engine along with any impurities that had already drained and settled. If your concerned stick a light cloth in the drain hole and swap. Its cold so not a problem to do this.

  • Welcome to the site. Glad to see you jumping in to help. I noticed you have given an answer to an old question that has an accepted answer. There is nothing wrong with doing so, but your answer directly contradicts the accepted answer. Do you have any reference to back up your claim? – CharlieRB Jan 10 '18 at 21:39
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I am one that supports the opinion of draining the oil when cold. The oil has had hours to completely drain off of the engine parts and collect in the pan. I understand the viscosity benefits of draining hot oil more quickly, however, the idea of stirring up all of those impurities by pumping it back through the motor just to warm it up doesn't make sense. I change my oil when I have time to let it sit for awhile so time is not an issue. This is just thought-candy... Anyone willing to challenge the prevailing practice with a little research?

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What happens when you drain the oil when cold? Nothing...

What happens when you drain the oil when warm? Nothing...

What happens when you drain the oil when hot? Nothing...

Using the correct oil and filter along with changing oil at proper intervals and maintaining correct oil levels are important things to concentrate on. Oil temperature during change is a non issue.

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