How important is it to drain oil hot?

[Tosh]

Huh, losing oil pump prime, who wudda thunk? I can only hope that possibility has been designed out of my engine.
Alright, obbob, I'm back to taunt you a second time. You make it sound like cold oil is running downward like sap trapping wayward ants along the way. But the kinetic energy of fluid (or anything) increases with the square of its speed, so hot and faster moving oil would have more energy to rip away whatever imaginary cling-ons you're pondering. And I refuse to brush my teeth in the middle of an oil change.
Yes, the dawn of the electric oil pump can't come soon enough: hit the oil drain switch, and the used oil is pumped out. Manually fill with new oil. Turn the key, and as soon as oil pressure is sensed, the starter engages. No more start-up wear, no more need for a new car. However, this isn't the way the market's headed: advanced oils and combustion control and long OCIs seem to be the trend (and a good thing).

 

[motorguy222]

Oil is a petrolium product with other chemicals/viscosity improvers added.

We all know that petrolium flows better when hot/warm.

While the oil pan is where the oil is stored,we know that certain elements are heavier than the oil and will settle into the pan.

The outlet on an oil pan is not completely even with the bottem of the pan,it has a small lip.

Since the outlet isnt even,the elements that have settled out of the engine most likely will stay where they are.

Take the same oil,get it warm/hot and mixed in the engine.The contaminants are now suspended in the oil so that they can come out more freely.

Look at it this way.

Try washing your oily hands with cold water and then warm.

Which gets them cleaner?

Now apply the same principal to an oil change.

 

[obbop]

I refuse to wash the inside of my engine with either cold or hot water.

But, I will continue pondering.

Ponder, I must. Ponder, I will.

 

[pepper32]

So anyway I have a oilpan heater (75 watts), gets so hot you cannot touch it with bare skin. Let's say I drive for about twenty miles then park overnight so everything flows into the pan. In the morning I plug in the heater for three hours and drain the oil. Since the oil flowed into the pan hot and then was reheated prior to draining, would that be the same as draining a hot engine?

 

[Tosh]

No, Pepper, you would've wasted that whole night plus the three hours (plus 810kJ of energy) that the (initially) hot oil could've been draining all that time....

 

[got boost?]

the oil mixes when run and holds more contaminants. prove it, take two samples one immediately after running the engine, one after letting it sit all night (both mid stream). of course don't let all the oil run out the first drain.

 

[Vstrom]

Do you want ALL the old oil out? Maybe not. I used to lean one of my motorcycles way over to one side and get a bunch more oil out. Thought that was clever of me.
Until one day I discovered there were deep pockets in the head designed to store oil for the cams, perhaps just for startup lube, don't know. Don't know how much running it took to refill them either. Anyway I quit doing the lean over to drain all the oil trick.

 

[Patman]

quote:

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Originally posted by got boost?:
the oil mixes when run and holds more contaminants. prove it, take two samples one immediately after running the engine, one after letting it sit all night (both mid stream). of course don't let all the oil run out the first drain.

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This is something I've been curious of, how would the oil analysis results differ if you took two samples like this?

 

[obbop]

Hmmmmmmmmm......

Interesting.

Time to ponder some more.

 

[Ramblin Fever]

Always have drained mine hot/warm, never cold. Yes that drain bolt is mighty warm, and I have a tendency to drop it into the dirty oil pan while taking it off - as it's too hot to hold onto.

I fish for it after an hour or so of the oil cooling off.

 

[blupupher]

quote:

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Originally posted by got boost?:
the oil mixes when run and holds more contaminants. prove it, take two samples one immediately after running the engine, one after letting it sit all night (both mid stream). of course don't let all the oil run out the first drain.

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Give me $20 and I will run 2 UOA's on my next OCI.

 

[XS650]

quote:

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Originally posted by blupupher:

quote:

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Originally posted by got boost?:
the oil mixes when run and holds more contaminants. prove it, take two samples one immediately after running the engine, one after letting it sit all night (both mid stream). of course don't let all the oil run out the first drain.

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Give me $20 and I will run 2 UOA's on my next OCI.

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Go for more money, you will need a particle count to prove your point, which I think is valid.

 

[blupupher]

quote:

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Originally posted by XS650:

quote:

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Originally posted by blupupher:

quote:

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Originally posted by got boost?:
the oil mixes when run and holds more contaminants. prove it, take two samples one immediately after running the engine, one after letting it sit all night (both mid stream). of course don't let all the oil run out the first drain.

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Give me $20 and I will run 2 UOA's on my next OCI.

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Go for more money, you will need a particle count to prove your point, which I think is valid.

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Well whatever it takes. I use Blackstone and was going to pay to have Terry read it again, so whatever it would cost over that. Does Blackstone do particle counts?
Or maybe use some of the z-report money for it, and I will send in 2 blind samples?

 

[Tosh]

There seem to be basically two discussions going on here: one is about whether hot or cold oil drains 'better' and the other is about whether the oil in the sump is a 'homogenous' mixture. When I drain hot oil into a basin, I can see streaks of different shades, so it's reasonable to assume that it is not mixed and there is some settling or separation beginning immediately after shut-off (or even before: it is a sump, after all). This would matter to me if I were sending some off for analysis: the sample should be a well-mixed representation of used oil. For a series of sample analyses to have diagnostic value, especially for a comparison between different vehicles or users, the sampling method must be standardized. 'Mid stream' seems too vague, and obviously this opens up a whole new(?) can of worms. But since I'm not getting it analyzed, I just want as much old oil out as reasonable (before I lose daylight). If I were obsessed with getting out every drop of old oil, I should be reducing my OCI.

 

[Vspec]

This conversation had great debate, time to revive it because the matter isn't closed and still up for debate. So. Bump TTT

 

[ex_MGB]

I thought the reason to drain a multi-viscosity oil warm, rather than cold, was to thoroughly mix the viscosities just prior to draining so as to preclude the higher viscosity component from hanging up in the engine innards?

I believe I have a winner here!