JShadzi at JShadzi at
Fri Aug 9 17:14:56 EDT 2002

Huw, your email assumes high EGT, correct?

Well, the EGT are originating in the combustion chamber, thus the piston is not the only place the heat is going, its going into the valves, into the cylinder head, and most importantly through 4 or 5" of exhaust port, which is directly surrounded by, yes, a water jacket.

You've isolated the EGT to only the piston, and disregarded its flow through the head which is heavily water cooled.  Also, high EGT will heat up the turbo too, which is also water cooled.

So, if you assumption that the heat is coming from EGT, then you have to assume that the real cooling system of the engine will be impacted by the increased heat, not just a little oil being squirted up at a moving piston.

Theoretically, I just don't see how high EGT can _only_ effect oil temps.  Its not that the oil and water are exchanging heat, its that they are both collecting the same heat from the same source, which correlates them.

Granted, there is the cooling capacity issue, and that the radiator has sooo much extra cooling capacity that it can shed all the extra heat witout the temp gauge budging, but, the temp sensor is located at the top of the water neck, before water enters the radiator, thus, you should see a quick bump in temps if EGT's are really that high and causing heavy heating of the oil.  Also, aside from all the explanations, this has always been my real work observation.


>> > it's not the head that heats the oil to 150 C, it's the two *really* hot
>> > places it goes, which are the turbo and the backs of the pistons.  Of
>> > course the turbo is also water cooled, so it is not such a factor.
>> > However, the oil sprayed on the pistons gets some serious exposure to
>> > heat, and then *is not* water cooled before passing the temp sender.
>> yes, that's true.  and plus the specific heat of water is so damn high
>> that I can buy that you wouldn't see violent swings in the coolant
>> temps.. but eventually a 150c oil temp HAS to transfer some heat energy
>> to the coolant.
>It does.  But follow the oil flow for a second here.
>The very hot oil from the back of the pistons falls back into the pan -
>no water cooling there.  Next stop, the oil pickup, then the pump, and
>the oil temp sender.  The oil has not yet given up its extra heat to the
>Finally it gets pumped around the block, head, and everywhere else,
>where it can drop some heat, via the metal which is hotter?  into the
>water.  Are there any places in the flow pattern that could truly be
>considered oil to water heat exchangers?
>Huw Powell

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