Oil Change on a Cold Engine

[Shannow]

Originally Posted By: SR5
but often to me the varnish pattern reflects the hot and cold parts of the engine cover, where the cold parts have the varnish. The hot oil lands on a cooler (but still warm) part of the engine cover, the oil cools a little and the varnish drops out of solution.


that's exactly how it happens in all of the industrial varnish that I've seen.

It always lays down where it's cooler.

 

[KrisZ]

Anyway, I used to think that the temperature did not matter, but ever since I noticed that a lot of stuff deposits at the bottom of the oil jugs where I store the used oil, I started changing the oil hot.
Now, seeing the videos about oil temp and solubility (thanks to Shannow), I have even more reasons to do it hot.

 

[CR94]

Originally Posted By: SteveSRT8

... Precisely. I have postulated about slow draining being an issue in certain engines with aftermarket drain valves installed. Some of them are markedly smaller than factory drain holes and thus seem to encourage a slower, less flushing drain. I have actually observed this in our trucks where Fumoto was used for many years. ...
That's plausible. The same would go for sucking the oil out through a thin tube.

Dumping it while hot and well-mixed is probably more important than the size of the exit, though, unless the oil is seriously lumpy.

 

[BrocLuno]

Originally Posted By: SteveSRT8


Another great reason for a hot oil change is your engine will have residual lubrication to protect it during a dry start with an empty oil filter...


After the very first start of a newly built engine, there is no such thing as a "dry start".

There is residual film all over every surface that lasts for months of sitting, if not years. A bit of a wait for a filter to fill is nothing that a motor can't easily handle at idle. If you are concerned, pre-fill the filter before installing ...

Ever been to one of those "dry engine" runs where you bet on how long a motor will run with all the fluid plugs out? Most will run over 20 minutes "dry" at well above idle ...

 

[4WD]

How to establish the right temp:
1. Get oil and filter ready
2. Slide ramps up to wheels
3. Drive up on ramps - kill engine
4. Do photo of oil and filter used
Temp is now just right to drain oil

 

[CR94]

No, you need to replace that Step #1 with a warm-up trip of at least 15 miles. You can "Get the oil and filter ready" while the oil is dripping.

 

[Nickdfresh]

I only change oil hot. I still have a scar on my arm from changing the filter on a smoking hot Mazda Miata that wasn't even mine. I would never change a cold sump...

 

[4WD]

Zero chance of that after all these decades - that Mobil 1 just drained fine - it was 82F outside and the motor was not much hotter ... drained it down to about 1/32" stream and Gold Plug back tight ...