Does engine REALLY have to be hot for oil change

[Stephanie]

Opinions please:

Our BMW mechanic does oil changes when the engine is cold. Mike_D says the engine should be hot.

I can see having a hot engine when draining straight 50 weight. Maybe it doesn't need to be hot in this modern age of reliable multigrade oils that might actually drain thoroughly when cold.

What do you guys think?

Stephanie

[OneWheelDrive]

Not to disagree with Mike_D. however, unless it is the dead of winter, I start and let the bike idle for about 5 minutes. Enough to get the oil moving and warm. Then I let it sit for about 10 minutes so the oil drains back.

But what do I know I mix oil with gas in the Aprilia.

[Stephen W.]

Sorry, no scientific facts here, just a long winded story. Take from it what you will.

The whole idea behind draining the old , (presumably very dirty) oil is to exchange it for new, clean oil. You don't want to have a quantity of dirty oil left behind. Back in the day it was felt that because hot oil flows faster it was always better to heat up an engine before draining it's lubricant. Also, that it meant that all the moving internals would have a coating of lubricant so less damage would be done when starting the engine after it's oil had been drained. But, having worked on hot engines a time or two I can understand why a mechanic would rather drain the oil cold. Problem is, he's on the clock and therefore can't wait for those last drops to make their way slowly out into the catch pan. So, new technology or not, you're going to end up with some old, left over oil in there. (Hot or cold.)
The questioned I posed to my father when I was but a we lad was: If the oil is dirty and we want to get it out then why do run the engine and push it up into places it will take forever to drain out of? Wouldn't it be better to pull the drain plug after the car, (or bike in this case) had sat for a long period of time so as much of the dirty oil as was possible was sitting in the oil pan? To which he replied, "And just how long do you think we should wait for it to drain?" To which my response was, "Overnight!" And so started the ritual of the 12 hour oil change.
Now, there are pro's and con's for both approaches. Bottom line is, change your vehicles oil regularly and you'll have no problems.

[Mike_D]

[Brian_Lees]

[Desmoquattro]

[Richard Rudd]

[Desmoquattro]