an oil cooler is the sign of an improperly built engine, period :evil:
[email protected] - 26 Jun 2005 06:09 GMT
> What of using aluminum, nickelsil plated cylinders, better heads and a
> full-flow oil system? Won't that bring about better cooling and performance?
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Nope.
Only 17% of your waste-heat 'budget' appears in the barrels. The
reason Porsche went to aluminum jugs was so they could devote more of
the cooling air to the heads. That is, the use of aluminum jugs was
one PART of an entire system of modifications needed to pull more power
out their engine and have it fit in the same chassis.
'Full-flow' doesn't make much sense. I assume you mean a full-flow oil
filtration system... which still doesn't make much sense because
filtering the oil doesn't have anything to do with cooling.
But if you meant adding extra oil cooling capacity... no again. To
produce more power without shortening the engine's service-life you
don't want the heat to get into the oil to begin with.
The latter point is one of the most commonly mis-understood
characteristics of air-cooled engines, which you often hear described
as 'oil cooled.' They're not. Indeed, ALL automobile engines are
'air-cooled' in that they must couple their waste heat to the
atmosphere. The lubricating oil serves exactly the same function in a
water-cooled engine as in an air-cooled engine, the only difference is
that the waste heat that appears in the oil of an air-cooled engine
must be coupled directly to the atmosphere, as opposed to being coupled
to an intermediary coolant as is the case with a liquid-cooled engine.
At high levels of output you're going to produce more waste heat. Most
of it -- about half -- blows right out the tail pipe but some appears
in the heads, barrels, piston and valves AFTER WHICH some is
transferred to the lubricating oil. The principle areas of transfer
are via the underside of the piston and the area of the cylinder-head
immediately adjacent to the exhaust valve(s).
The problem here is two-fold, the first being that oil is not an
especially good coolant, the second is that the RATE of transfer is a
function of the surface area, the rate of coolant-flow and the nature
of the coolant itself. Simply clapping on a bigger cooler addresses
only the heat that has ALREADY gotten into the oil, which is only a
small part of the cooling equation.
The VW's heads and jugs were designed for a rather modest level of
waste-heat management. When you generate waste-heat at a greater rate
than those designed limits you end up with excessively high
temperatures in your jugs and the areas adjacent to the exhaust valves
-- temperatures so high they COOK the oil rather than simply transfer
the heat. The remaining oil does pick up a lot a heat but those areas
are still hotter than they should be, resulting in greatly accelerated
wear and possible detonation.
But it looks good on paper, right?
Just give the man your money,
bolt on an oil cooler the size of a barn door and bingo! No worries.
Unfortunately, all you've done is treat the SYMPTOM. The problem --
the excessively high temperatures -- are still there.
Thermodynamics does not respond to Convential Wisdom. Any more than
engineering responds to the Democratic Process. The fact a majority of
your buds -- and all of the folks trying to sell you stuff -- say a
bigger oil cooler is the way to go doesn't mean it is.
-Bob Hoover
