Coolant temp. and engine temp.

[KARL C CHEN <karlcchen@domain.elided>]

There are some misconception about coolant temperature.  
as relative to engine temperature.  A lot of people got
worried when they see water temp goes high thinking 
that engine temperature is high too.  Most of case
it is not true.

Unless your engine like most aircraft engines that has
CHT( Cylinder Head Temperature ) indicator.  Otherwise,
on most car with engine oil temperature indicator, 
it is a more accurate indication of engine temp.

Here is what I observed at cars equipped with oil temp. 
indicator.  When you stuck at traffic idling, the water 
temperature goes high.  But oil temperature is  actually 
dropping.  The reason the coolant temp. goes high
is not because engine is running hotter.  It's high is
because engine speed is slow thus coolant pump pumps
much less coolant into engine. Coolant stay longer 
inside engine block to be heated.  Noted almost all 
coolant temp. sensors are located at where coolant came 
out of engine block. 

When engine( or car car ) is running fast, the oil temp. tends 
to go high, but coolant temp. is actual much lower than idling.
The engine is actually running hotter than idling, but 
coolant has less time to be heated by engine.

Karl



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