Ed Hughes

Does that mean you infer no benefit?

inkatouring

No. Assuming the answer to my original question is no, the only benefit I'm aware of is that warm oil "adsorbs" contaminants, so you get more dirt out. I'm sure there is an optimal temp for that. I was always taught to warm the motor, but that it need not get to operating temp. My curiosity was whether that was different with our Porsches combination of oil coolers and dry sump, as some have implied.

Slow Guy

Personally I would use the term suspends rather than absorb. Think of it this way, take a 1 gallon jug of tea, if you just pour it out a glass at a time by the time you emptied the jug there would be a fair amount of sediment at the bottom of the jug. If you shake the tea before pouring there will be very little sediment left in the jug when it's empty. Much the same as warming up the engine first.

There is no way you can get all the oil out of an engine w/out disassembling it, there are just too many places for puddles to collect. The idea is to get out as much of the contaminants/sediment as possible no mater what percentage of the total oil you drain.

GC96

I would think that in theory the hot oil would help drain more oil out in two ways. First the viscosity of the oil would be less than when at room temperature and it should flow a little easier and be less likely to stay stuck to engine components. The second way it should help is by causing the oil to expand and reducing the density of the oil. It might help to think of the oil in terms of mass rather than volume, so when you fill up the oil your putting in a certain mass of oil which happens to take up 10 quarts at room temperature. When the oil is all at operating temperature it should take up more volume than 10 quarts. Since the oil cooler system is a fixed volume, having it filled with hot low density oil once the thermostat opens minimizes the mass of fluid in the system. The rest of the mass of oil is back in the tank. So in theory draining when the engine is hot should allow you to drain a higher mass of oil than when it is cold. Now does all this add up to a significant quantity? I'm not sure it does.

GC

inkatouring

Thanks GC, an intelligent and thoughtful response to the actual question asked. Food for thought....

AOW162435

I only drain my oil when it's tepid.


Andreas

Mark in Baltimore

You always told me flaccid.

IXLR8

But only if one is "teppert". One would need to recognize the dialect.

Amfab

oy

JasonAndreas

I always do it as close to cold as possible.

Matt Lane

Careful gents, you might yet end up honorary RennSpoon members...

Mark in Baltimore

heynowi'msurei'mnotcleanenough

FlatSix911

If I do it ... stone cold
If my wrench does it ... nice n' hot

geolab

The oil Thermostat open or close difference, is the amount of oil in the tube from the thermostat to the oil radiator.
remember the oil cooler is top fed
the return oil tube from the cooler to the oil reservoir has no thermostat, flap, or other restriction.
this is where the gurgling occurs when thermostat opens. Air is present in the return tube.

In real life= After calm driving, park the car leveled with temp. gauge hot at 9 o'clock and let idle for 30 secs. (for the example) lets say oil level gauge on dash reads at 3 o'clock
Now floor the accelerator and rev the engine above 6000 rpm twice or three times and let idle, yo will notice the oil level gauge will shoot up far more than 3 o'clock.
But the difference? maybe 1/4 of a liter +/- or 2% ? I don't know
I change my oil hot, because I do not have to wait, cold takes longer time to drip out as said above

911Dave

Warm is plenty good enough. Hot is too hot; you'll burn your hands on the oil and the engine components while working under there. There's not enough oil in the oil cooler lines and oil cooler to make any difference in the health of your engine, provided you change the oil at least once a year or every 5k or so, whichever happens first. Warm is good enough.