The water is there for the specific purpose of removing excess heat from
the engine. For this reason it passes as close as possible to the
sources of the greatest heat - around the combustion chambers, the
cylinder head and cylinder bores. The oil has the primary purpose of
lubricating the moving parts of the engine - in particular, the
crankshaft bearings. Some oil does go to the head, to lubricate the
valve gear and some is sprayed onto the cylinder walls but not,
necessarily, close to the heat sources, and not in vast quantities.
Peter Bell - firstname.lastname@example.org
hmmmm, oil splashed up the bores must touch the underside of the pistons.
These being aluminium the oil must be close to combustion chamber temps.
Aluminium is a first class conductor of heat.
I suppose my temps are close enough for the theory to stand.
Also the oil is not cooled down as well as the water.
It's not necessary since the oil works fine in much higher temperatures.
In my Audi the oil is cooled (and preheated for that matter) close to the
At certain speeds (revs) the oil and water are both 90 degrees Celsius.
Also, oil and water have quite different Specific Heat Capacity values.
SHC is the amount of energy in joules, required to raise one gram of the
substance by one degree kelvin.
Liquid water is 4.186 joules, I expect engine oil is higher.
Not an answer to your question, but I'm just curious, where are you getting
the water temp info from? Hopefully not from the water temp gauge in the
dashboard, as that thing is programmed to stay right on 90C regardless
whether the coolant temp is 90C or 80C or 100C.
Let me be more specific. The coolant gauge on my '01 A4 behaved that way.
It had a dead range in the center, and it was designed to stay there and not
alarm the driver if it was a few degrees below or above 90C. Maybe it was
betw. 85C and 95C, I can't remember. Only if something was seriously out of
whack (big temp change) would the gauge move to the left or right of the
center. This could be easily monitored on the digital coolant temp display
in the climate control section - the temp would fluctuate a few degrees here
and there while the needle on the dashboard would not budge from the center.
You're not hearing what I'm saying. If this is a problem with you not
believing me, just go onto the B5 A4 forum on AudiWorld - everyone will
confirm that the coolant temp gauge on those cars has a dead range.
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