On Wed, 2011-07-20 at 08:47 -0500, Dave Mcneely wrote:

>  Bottom line, I think the oil has a major heat source, and only if an
>  external cooler has been added does it have a real functional way to
>  dissipate heat other than to the coolant through metals that both
>  contact and through such things as the sump.  The sump is like a
>  reservoir of liquid, it cools slowly compared to a radiator.   The
>  coolant has a large heat sink, and thus has a temperature gradient.
>  That gradient includes the oil.

So what we're saying is that the oil is in contact with some really hot
bits, and because there is high thermal resistance between the oil and
the coolant, the oil can climb to much higher temperatures than the
coolant.

It doesn't help matters that the hot oil drains down to the sump which
isn't cooled by anything except the hot pavement under the engine!

Others have also explained that while the water pump can move a lot of
coolant up to the heat sink in the front, the little oil pump just chugs
along pushing the oil more slowly and in lower volume so that even if
there was an external oil cooler the size of the radiator, the stuff
ain't moving fast enough or in enough volume to cool the really hot bits
it's in contact with like the coolant can for the hot bits it is in
contact with.

I think I've arrived at point where I have a better understanding of why
the oil temp gauge shows higher peak temps during high engine demand
than the coolant gauge shows -- which is the answer to my original
question! Many thanks to all who have taken the time to respond to my
inquiry!

-- RJS