Running hotter than normal can be caused by three things - engine producing
more heat than it should, cooling system can't get rid of as much heat as it
should, or the gauge is simply reading too high. However if the fans are
coming on sooner than they used to as well that does imply it is indeed hotter
coolant and not simply the gauge.
First check the gauge by measuring the coolant temp with another device, not
so easy on cars with the remote expansion tank unless you remove the radiator
plug *very* carefully, having removed the radiator cap first, also very
carefully.
Retarded or over-advanced timing will cause it to run hotter, as can weak
mixture. Check dwell as well.
Check the surface of the radiator for cool patches i.e. blockages, an
infra-red (laser guided) thermometer is useful for this but the sensor does
need to be as close to the surface as possible even with a 10 to 1 aspect
ratio.
Go for the easy stuff first, none of the above require much by way of invasive
surgery.
Unless the thermostat is faulty in that it isn't opening fully replacing a
working 180 with a 160 won't cause it to run cooler if it is running hotter
than it used to. You can take the stat out and test it by dangling it and a
thermometer in the water (not resting on the bottom) of a pan of water and
bringing it up towards the boil. Having gone that far you might as well
replace the stat anyway, although these days putting new stuff in when it
isn't needed can introduce further problems with the poor quality of new parts
these days.
You could do a compression test, and a cooling system pressure test, in case
you have a small head gasket leak into the water jacket.
After that you are down to reduced flow through the system, possibly because
of blockages elsewhere, possibly because of impeller problems as you say.
And it is only running slightly warm as you say in the text, not overheating
like you say in the subject. If it isn't steaming or losing coolant it isn't
overheating, although any change in 'normal' behaviour is always something
that should be investigated.
PaulH.
----- Original Message -----
My 80B is running too warm. It used to run one needle
width to the left of center no matter what the outside
temperature. It now runs 1 - 2 needles to the right of
center, and the fans come on when moving at 20 MPH or less.
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