Better to change oil with engine (oil) hot or cold?

i don't think there's any agreement. i like it hot, pull the plug, and let it drain for a few hours.

when you take it somewhere, it's warm to hot, they change it and you're on your way. unless you drop it off the day before.

 

Warm

 

I will usually change it warm....letting it drain for 30 minutes once filter has been pulled.

 

Warm. Meaning let it sit for a half hour before pulling the plug.

BUT.......don't worry about it. Really.
The few ounces of used oil remaining in the upper engine if you do it hot immediately after stopping will NOT cause a problem.

 

Just not cold.

 

The point an oil change is to help get rid of the debris and contaminated oil. Warmer oil will probably flow better so more oil will probably drain out when hot/warm.

I would say the better point is to run the engine a bit to help circulate oil around and suspend the debris. It helps you get rid of more junk when you drain the oil.

I just drain my engine cold. In the end, the force of gravity will get most of the gunk out. Any other effort leads to very little gains.

 

The takeaway here is to avoid those 5 minute quick lube places, that barely let the oil stream stop before plugging it back up to get you out the door.

Do it yourself.....pay a neighbor....or your trusted mechanic

 

I've never seen any difference, hot or cold. It drains faster hot, but if you're not in a "real hurry" it makes no difference. As far as "suspending stuff" in the oil, if it's that dirty you have -real- problems. I find "hot" is more trouble doing it myself (don't want to get burned). Because the GIII Prius is so low, and has to be raised so far to open the oil filter change door, I -have- to drive it up on ramps, and that does warm up the oil a bit. But it's not "hot".
Do keep in mind that the Prius carries 3-4 litres/quarts of oil. Leaving 3-5 ccs in there IS NOT going to make any difference! You ARE NOT cleaning the engine interior by changing oil!

 

And THAT is usually how you GET the oil to be hot or warm before draining it out.

 

if you drain it hot, be careful, it's hot! goggles, gloves, face protection, etc.

 

I drain it cold and put the plug back in as soon as the flow has almost stopped. I'm not that worried about the last bit. The only way you will get the sludge out if its built up is to pull the oil pan. Some people warm their cars up for 5 minutes before driving. It's all preference there isn't really a right or wrong. Whatever makes you feel good.

 

Checking oil level directly after shutting down, vs hours later: I see no noticeable difference. Also, I did an oil change a couple of days back, with air temp slightly below freezing. I needed to pour some bulk 0W20 into a bottle afterwards, and it was pretty slow flowing.

As I said in the other thread: you have to drive the car anyway, do your oil change right after a drive seems like the smart money.

 

This.

Back in the day when oil came in CANS, maybe temperature made a difference in getting a good oil drain, but now most every oil is so viscous (even in very cold temps) that it flows well. Hot drains faster, but if time isn't an issue, just let it sit longer before putting the plug back in.

 

Looking in the Toyota Prius Repair Manual, I see no mention of engine temperature in the oil change instruction. However, looking in the Honda Shop Manual for a previous car, step one is:

1. Warm up the engine.

Take your pick. Personally, I know the oil flows easier when hot, and I suspect particulate will be more homogenized when the car's been recently run and warmed up. It's by no means difficult to do oil changes right after a drive, so that's what I do.

But yeah, either way you'll get it done.

 

If it is not causing a problem, why bother ??

 

I like that attitude and I share it.......to a point.
IF it is likely to cause a problem in the future, by all means fix it.
IF however it is NOT likely to ever cause a problem, then don't obsess and waste your time and money; especially if nobody can see it but you.

How often do you replace the scraped up/slightly bent air dam under your front bumper ??

 

Yeah with some mainly cosmetic items, I'm loath to react immediately, you know it'll be hit again before long. And if it's plastic, down low, meh. One thing, I'm all over missing fasteners, because neglecting them can cascade.

But radiator support bent might be good to mend/replace.