There are two terms in this temperature equation.

One is steady state thermal transfer rate. If you generate a
quantity of heat say one BTU then it will raise one quart of oil X
degrees F. If you add two times as much heat to the same oil it will
raise the temperature of the quart of oil 2X degrees F.
At any given RPM the oil pump will pump "Y" quarts of oil per minute
whether you have 2 quarts or 10 quarts in the sump since the pump is a
gear positive displacement pump. This means that the oil will carry
of the SAME amount of heat per minute if the temperature delta is the
same. If you want to get rid of more heat then you have to pump the
oil faster or heat the oil hotter to get a larger delta temperature
difference. This is the steady state condition. This is the condition
the engine is in when the temperature gage quits moving up.

The other part of the equation is the transient part that occurs on
warm up of the engine If one BTU will rase one quart of oil X degrees
then it will take ten BTUs to raise ten quarts of oil X degrees. It
might take an extra two or three minutes to raise the extra 8 quarts
of oil to the final steady state temperature. Once this temperature
was reached the extra 8 quarts does nothing for you unless you have a
big leak and start dumping oil overboard in which case it gives you
some more time before the oil all runs out.

If you put too much oil in the engine such that the crank shaft hits
the surface of the oil in the sump then a lot of mechanical energy is
transferred into the oil which heats the oil excessively due to the
excessive splashing.

The end result is the oil and engine temperature will be the same in
less than 30 minutes whether you have 2 quarts or 10 quarts as long as
the crank is not hitting the surface of the oil or you are not sucking
air into the pump due to low oil level at the pump inlet.

On Thu, 02 Sep 2004 01:29:49 GMT, "Jay Honeck"
wrote:

I thought Jay's experience of no change in temp was enough data.

I don't see how you can conclude anything from the fact that the temperature
gauge reads the same.

If the oil cooler is working properly, it should keep the oil at a
steady-state temperature. In order to achieve that steady-state, it my have
to work much harder (I.E.: The thermostat may have to keep more oil flowing
through the cooler in order to maintain that steady temperature.) with less
oil on board to provide cooling.

This seems intuitive, but I honestly don't know enough about thermal
dynamics and engine design to conclusively say anything one way or the
other.

What we're not able to measure is how much "easier" it is for the engine to
remain at the a relatively cool 180 degrees, now that I've got 12 quarts
flowing through it instead of only 8.

I suppose the way to prove (or disprove) this theory would be to push the
engine to the limit, first with 8 and then with 12 quarts of oil on board,
and see if it overheats more quickly with less oil on board.

I suggest we try that with one of *your* engines first...

;-)