Huw Powell human747 at
Fri Aug 9 18:13:38 EDT 2002

Well, first, there are two issues raised in this thread.

The first, and important one, is Marc's apparent high oil temp while
cruising at part throttle, which will, as you and others have suggested,
best be approached by a combination of tweaking his fuel delivery,
directly measuring EGT, and perhaps using a more reliable oil
temperature gauge.

Second, and far lower in importance, more like the "after the race"
chat, than the race itself, is this "issue" of the oil and water temps
seeming to be "unrelated", or at least related in a complex way.

> 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.

Well, first, yes, under any particular condition, the oil and water are
going to be heated in a consistent ratio.  But the oil will likely show
a much wider range of temperature as a result of this due its lower
specific heat, and remember, if there isn't much of an "overheat"
condition to the water, as it goes up a few degrees the thermostat opens
more, balancing it.  I would hazard a guess that over 120 C the oil
thermostat is wide open and can't change anything as the oil goes up
(faster than the water).

IE, under these conditions the oil "cooling" system is already maxed, so
the oil temp rises steadily to some equilibrium level - where the
increased temp finally dissipates as fast as it accumulates, via the oil
cooler, oil pan surface, oil to water transfer, etc.  In the meantime
the water cooling system is not stressed and so maybe only fluctuates by
5 degrees, barely noticeable on the gauge.

> 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.

I agree there, as far as the coolant temp sender location.  It is at a
"hot" location.

The reason for my focus on the oil sprayers, is that this is the one
place where oil can gain heat (pushing its temps up fast) that is *not*
water cooled.  The head, the block, the turbo, all places where th eoil
can pick up heat, are also bathed in water jackets to keep them from
overheating.  The piston isn't.  of course this is why those with more
experience at blowing up engines see nifty holes in their pistons -
right?  They get the hottest when things are out of control (or at least
out of the "happy" range).

Remeber the schematic, though.  The oil is probably getting *cooled* as
it flows through the nicely water-cooled head, but the heated oil from
the sprayers gets to the temp sender prior to any appreciably cooling.

Of course, knowledge as tot he relative amount of oil taking all these
different paths through the engine would be a nice bit of info.

But as I pointed out earlier, most of this wondering and theory is
irrelevant to the "problem."  Sure, the oil temp will vary wider and
faster than the water temp, for the reasons I have been struggling to
write about.  But if Marc has an EGT problem at some running condition,
the solution is more and better measurement combined with some tweaking
of his EFI tables.  Which might even be fixed by now after he gets to
play with your numbers - which have more time (and measurement) put into
them so far than the East Coast contingent has had the opportunity to

I'm not debating your vaster experience or expertise in this area...
just trying to put into words a series of long term layman's
observations and thoughts on this little sidebar to the main question.
And of course, as we all know, I might be totally wrong - but I'm a -
dancing fool... yeah!

(garages have more uses than just working on cars!)

Huw Powell

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