Cooling Airlocks and Water Loss

No. The crap that settles in the sump tends to form a solid lump in the places that don't get agitated much, and does no harm. Crap that gets stirred up as you suggest is caught by the filter. Changing engine oil when warm is basically a hangover from the days when it was so thick it would be like treacle when cold. There isn't really a reason for it with modern oils.

Steve

However, we're talking about a 1940's engine that uses 1960's oil (20/50)

- modern oil is pissed out at an even faster rate than the "Classic" stuff.

Were talking Jaguars here and they like 20-50. three out of four cars in my shed use 20/50.

Some time ago I reconditioned my MG engine, at the time was using Castrol XL 20/50 then they released this new oil Castrol GTX 20/50 (or 40??)

What did happen the pressure difference did not protect the engine and I pulled the engine to find the big end bearing journals blue and had to replace the bearings and run the older oil XL again.

I still run XL 20/50 in all the BMC products in the shed.

Multigrade oils are sufficiently modern as not to turn to treacle when it's a bit chilly.

AFAIC the only reason for draining oil when warm is so that it's neither too hot nor too cold as it trickles down your sleeve.

Steve

I've yet to find any oil that flows as easily cold as hot. And by quite a margin. So always drain oil from a hot engine.

In message , "Dave Plowman (News)" writes

Cold oil which is as free-flowing as hot oil is defying the laws of Fizzicks, regardless of what oil companies claim for multigrade.

Anyway, I used to find it a more pleasant sensation to have warm oil flowing up my arm as I removed the sump plug... ;-)

which is the reason to buy magnetic sockets, then you can avoid the oil, hot or cold.

It happens *once* to most part-time mechanics, I suspect...