Oil coolers

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

"mikem" wrote:
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).

You are just splitting hairs. No, oil is not dumped out of my
airplane's engine taking excess heat with it. Neither is water dumped
out of my car's engine, yet the car engine is still a "water cooled"
design.
--
Dan
C172RG at BFM

On Tue, 12 Aug 2003 16:30:14 -0500, "Dan Luke"
wrote:

You are just splitting hairs. No, oil is not dumped out of my
airplane's engine taking excess heat with it. Neither is water dumped
out of my car's engine, yet the car engine is still a "water cooled"
design.


But there are not many cars without a radiator, either! (except
dragsters). I haven't seen a "water cooled" car for more than fifty
years. Nowadays, they use a witches brew of Silicates to carry heat
from the block to the radiator. The cooling takes place when air blows
through the radiator...

MikeM

Mike, you live in a different universe than I, apparently... Most
everything you say here violates what I know to be engineering fact, and
thermodynamic necessity, after a lifetime of building up and burning down
engines...

Oil absorbs internal heating of engine parts from both combustion and
friction and transfers it to the external metal of the engine (primarily but
not limited to; oil pan, rocker covers the big two, crankcase, and
propellor hub, and a cooler if present) and that metal then transfers the
heat both convectively and conductively to the external world...
Up to 40% of waste heat is transferred out of the engine by the oil
according to this source http://www.uccc.co.uk/when/hycwoil.htm
- actually that looks a bit high and I tend to size my calculations on a 33%
basis...
See also
http://www.usace.army.mil/publicatio...-691/chap9.pdf

http://www.perma-cool.com/Catalog/Cat_page02.html

Engine cooling is a science, not guesswork, and there has been millions of
dollars spent on research since the invention of the internal combustion
engine as a prime mover... In ten minutes I could amass dozens more
authoritative references, but I suspect it will be wasted effort...
Have a good un...

Denny

"mikem" wrote in message