DDK - Die Deutschen Klassiker

Over the very many years of changing oils on many engines I've always wondered the merits of draining oil hot or cold. In my cases i have two changes to do where both 911 engines have stood still since October 2022.

Is it worth/best to start the engines with the old (very low miles) oil and then drain hot so the inner parts have been washed off, or drain cold where the last year's oil has really dripped down to the sumps?

Done it both ways on many occasions, but is there a validity to either approach?

Most obvious one is you don't get scalded draining cold!

I will add my 2 pence worth on flat fours. Jack Staggs, who has been working on 356s since the 70s, says cold. The idea is that the warm oil all drains into the sump. Then you open the sump and get all the oil out. With a dry sump I assume it's similar. You still want to give the oil time to drain from the engine?

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Yes, I usually do this all stone cold and after a long static time.
Once read that starting it up and getting hot flushes any corrosive elements from the engine internals, but any corrosion would have occurred in the 5 monhs of rest.

I always do it warm / hot when the oil is more free flowing and I'm likely to get all out. I still leave it to drain over night though.

In theory, with any cars with front oil coolers, you should really get the oil hot enough so the thermostat is open and then in theory you can drain from the oil pipes too ... I've never done this and just accept there is a litre or so of old oil still circulating ( not too much of an issue if regularly changing ) .

Always hot here, nothing better than oil burnt finger tips!

If you have a front cooler you not getting anything out of that and associated lines whether hot or cold unless you start disconnecting hoses, which can then lead to other issues if they've never been apart for 20+ years.

Always been told do it hot presumably so any crap is then moving about suspended in the liquid and will come out when you drain it.

I can’t see that you can rely on all bad stuff going to the bottom of the engine when it’s cold - some crap will be stuck in other parts of the engine.

I’m going now as I’m starting to bore myself

Where you going Mark, anywhere exciting?

I would say that if when the engine was last run it was up to temperature when switched off - then as much of the contaminants will have returned to the pickup sump as there would be if you were to run the car up to temperature again.

I would imagine that the reasoning behind changing oil when it is hot is speed up the draining process. Not many people would go for a cold drop if the instructions read 'Drain the oil for at least a week'

As you have already been draining the engine oil back to the sump for the past months - surely just drop the oil! (preferably overnight)
The majority will be in the oil tank anyway and that will drain easily hot or cold.

I think you can overthink these things.

It will be done cold.
The last time the 2 engines ran they were stinking hot, esp the Lola's and then shut off so all the hot oil had anything from the engine suspended in it.
4 months to drain to sump for both.

I always leave the engine and dry sump tank plugs out until the dribble stops. No point taking longer as the volume in the coolers is FAR greater than a dribble...

The oil in the 911 will have done about 2500 miles, the Lola's about 40 miles.

911hillclimber wrote: ↑Tue Feb 14, 2023 4:58 pm It will be done cold.
The last time the 2 engines ran they were stinking hot, esp the Lola's and then shut off so all the hot oil had anything from the engine suspended in it.
4 months to drain to sump for both.

I always leave the engine and dry sump tank plugs out until the dribble stops. No point taking longer as the volume in the coolers is FAR greater than a dribble...

The oil in the 911 will have done about 2500 miles, the Lola's about 40 miles.

Which just leaves the burning question of which oil you are using

For 3 decades now I have used Shell Helix ever since Bob Watson told me to.
Is it the best? Goodness knows.
Is it the worst (for my engines) goodness knows, but I'll stick with it.

911hillclimber wrote: ↑Tue Feb 14, 2023 10:49 pm For 3 decades now I have used Shell Helix ever since Bob Watson told me to.
Is it the best? Goodness knows.
Is it the worst (for my engines) goodness knows, but I'll stick with it.

Funnily enough it’s also been my go to oil on all the older cars.

Just bought a 20 litre drum from these guys for £90 inc very efficient next day delivery.


https://www.ebay.co.uk/itm/392277403770 ... olid=20006&

Thank you for that link, first time I've seen it in 20L form, good saving!