On Mon, 11 Aug 2003 15:04:58 -0400, "Dennis O'Connor"
wrote:

Don't underestimate the amount of heat the oil removes from the engine...
It is critical... Without it's help pistons would burn up within minutes,
valve springs would overheat, etc...High powered engines often have a an oil
spray directed to the bottom of the piston...

Yes, but spraying oil on the underside of the pistons does nothing to
remove that heat from the engine! The oil just carries the heat from
the piston into the oil pan. The piston/cylinder is cooler than it
would be without the oil spray, but the oil/lower end of the engine is
now much hotter. This is why I said that oil just reduces temperature
gradients. Getting the heat out of the lower end is another matter
entirely.

How does the heat get carried away from the engine's lower end? If the
engine has no oil cooler, then the temperature of the lower
end/crankcase/oil pan will stabilize when the heat being carried away
by the airflow through the cowling just matches the heat being
produced inside the engine (convection). Heat loss from the engine due
to radiation does a very small part of the total heat flow.

The oil cooler is needed where
the oil pan, case, prop hub, and tappet covers, cannot radiate the heat load
adequately...

I prefer to think that this is just a choice made by the designer.
Clearly in high performance engines/aircraft, it is advantageous to
"concentrate" some of the heat transfer from the engine to the cooling
airflow into one spot, which we call an "oil cooler". As I have
already pointed out, this makes possible automatic regulation of oil
temperature, and LoPresti-small opening cowling. However, there are
many aircraft flying without oil coolers, so a cooler is not
mandantory

The reason I got into this thread in the first place it to try to
dispell the OWT that you cited above: "Don't underestimate the amount
of heat the oil removes from the engine.". If an aircraft has no oil
cooler, then the amount of heat removed from the engine by the oil is
ZERO! (Unless you have a BIG leak).

MikeM