Is it really important to change oil when it is warm?

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Jun 29, 2005
E. Texas
I've read several threads that talk about changing oil shortly after a car has been driven a while. Why is this? Is there any harm in changing oil when the car has sat for a few hours, or even overnight? It seems to me that if a car were just run it would be too hot under there especially if hot oil shot out all over your hands. How long does the engine need to run before changing oil - 10 miles, 20 miles or what? Maybe the oil needs to circulate a bit if you are changing it in below freezing weather but is there any harm in parking your car at night and changing the oil in the morning if the temps are moderate? It also seems to make sense to me that the oil would sort of "settle" in the pan overnight and the change would be more efficient but I just don't know the mechanics of oil "circulation" enough to be sure about that. The reason I ask is that I will change my oil/filter this weekend (first time I've done my own change in over 20 years) and would rather try it cold so as to not scald myself if I make a mistake.
I think the logic is that the warmer oil is, the better it flows and the more of it you can get out when you drain it. Personally that is the theory I subscribe to myself and get my vehicles warmed up before I change the oil. It may not really make a difference.
There's no harm in changing it cold. Changing it warm simply makes for a better oil change. I agree with changing it cold for your first oil change. Everybody has their own way of dealing with hot oil. Though running the car for just just a few miles won't make it too hot to touch, it'll only warm the oil up a bit.
I get my engine good and warm and then go inside and watch tv or surf the computer for 30-40 minutes. This lets the headers and motor cool enough that I don't get burned, but the oil is still warm and drains nicely.
for your first few oil changes i could see it helping you get used to doing it when the car is cold. but when you get better at it do it while the engine is hot. you can move the plug and the filter quicker and you know what to expect. i worked at a jiffy lube for 4 years and only on a few cars did the hot oil bother me. what is worse than hot oil is if the oil filter is in a stupid location where you have to move your arm around a hot exhaust. what really help is to take a rag or two and wrap it around your arm, reduces the risk of getting burned by a lot. its also nice to wrap a rag around your wrist when doing a fuel filter to keep gas from going down your arm.
Get yourself a pair of Mechanix Gloves and a box of Nitrile gloves from Harbor Freight. Put the Mechanix gloves on and put a Nitrile glove on top. No hot oil on your skin, hot oil filter doesn't burn, and no oil on your gloves.
Martyi, I buy a 50-100 pair of latex or vinyl gloves and wear a pair during an oil change which I like to do with the oil hot. You can find them at Wal-Mart, drug stores, etc... Look near the bandages. It is probably a good idea to keep oil off your hands as practically possible.
good point rusty. used motor oil is know to cause skin cancer, i think its because of the unburned hydrocarbons. but for the most part i think a person who does their own oil changes shouldnt have to worry about. there is also stuff called barrier cream that acts as an invisible glove. it prevents the oil from soaking into the skin. it works pretty good.
used motor oil is know to cause skin cancer
It would be interesting to find out how this is "known." I suspect lab rats were grossly overdosed with used oil to the degree we would never see in a lifetime. Nonetheless, its a good idea to avoid soaking various chemicals into your skin. As for the topic, I don't see a problem with a cold change (well, maybe if it is zero degrees out). It can help minimize the amount of oil that spills out when you remove the filter. I would not do it, though, if you had run a cold motor just a minute to drive from the bottom of the driveway into the garage, because then a lot of the oil will stay up in the engine. But if the last trip warmed the oil up sufficiently, you should be fine.
I dunno i guess i've gotten used to the heat. I mean you just have to when people come off the road and want an oil change ASAP usually its tolerable, but yes sometimes its just scorching hot. I can usually get away with wrapping a rag around my hand and then spinning the filter off.
Okay guys, thanks for the tips. Although it looks like changing the oil cold will not hurt anything, the general feeling seems to be that the oil should be a little warm anyway to achieve the best drain - but not necessarily hot. I think I will drive to the grocery store tomorrow (20 mile round trip), let it sit about half an hour or so just to cool a little and then change the oil. It is in the 60s here so the temps are moderate. I will take the advise of wearing gloves and a rag on my arm for sure. I plan to install a Fumoto drain as well so this will be my first (and last) "real" oil drain in many, many years. Thanks again.
Cold oil simply takes longer to drain. That is the only downside. If the contaminants are truly out of suspension, they will be at the bottom, and drain out first, anyway. I don't think things separate out, unless you have a severe engine problem with heavy metallic paticulate matter in the oil.
"It seems to me that if a car were just run it would be too hot under there especially if hot oil shot out all over your hands." I don't play it cool. The hotter, the better. [Big Grin] We BITOGians wear our oil-change burn scars with a deep sense of honor. Seriously, I rarely get more than a few drops of oil splattering on my hand ... even fiendishly hot, I never get burned. Depending on how long I am poking around doing an oil change (letting it drip to the Nth degree) ... and if the water is turned on down at the garage ... I will wash my hands more than once throughout the procedure. No worries there for me. [Razz] I like doing changes with the oil as hot as I can get it. Like Mitchc Alsup says, the best time is after a multi-hundred mile trip. Everything is as stirred-up as possible. Once things cool down, the worst of the ick will settle at the bottom of the pan (especially overnight) ... and unlike mechtech, I don't believe this stuff will simply drain out first. I think once they've settle onto the pan, they aren't easily moving ... especially in cold oil. He is right about most of the metal particles being in your filter. However, I work on a lot of outdoor power equipment and I see changing the oil in those engines boiling hot as essential as most don't have a filter. And merely looking at the oil after it has drained shows all kinds of silvery bits in it. How many of those would have stayed inside the motor if the oil had not been thoroughly mixed up, hot and runny when drained? [Confused] I have a Honda tractor with a hydrostatic transmission. the fluid, when new and/or cold looks perfectly clear ... like baby oil. However, when I drained this stuff, it was hot ... after at least an hour's running. The hot used oil came out looking fairly dark. Some like it hot. I know I do. --- Bror Jace
A hot drain is better than a cold drain, but a cold drain is better than no drain. After changing oil for 40 years, I finally learned about disposable vinyl gloves. [Duh!]
Its important to let the car sit for a while after warming before draining, give some time for the oil to drain back from the upper end.
Thingfish, I don't understand why it should sit before draining. Won't it drain back from the upper end while the pan is draining?
Depending on the design, it could take quite a while for a lot of the oil to drain down from the upper end. I think this is part of the consideration of a cold drain vs a warm drain. With a warm drain, there is oil left in the upper end of the engine as the vehicle has been recently operated. With a cold drain, particularly one done "first thing in the morning", the oil may be cold, but it has all drained down to the pan. I guess the ideal would be to do your own oil change, draining late in the day when the engine is warm, but letting it drain overnight and refilling the next morning.
draining late in the day when the engine is warm, but letting it drain overnight and refilling the next morning.
Once, my oil pump lost its prime. Just sitting overnight not even changing the oil. Since then, I have never let the car drain long when changing oil. Also, getting the job done faster reduces risk of someone driving the car before oil goes back in. Or of forgetting to put oil in.
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