On Wed, June 15, 2011 9:56 pm, YES NOPE9 wrote:
> circa 1990   same engine , replaced water pump 5 years ago.
> gradually overheats on long drive
> no coolant is missing
> fan belt is quiet ... does not appear to be slipping
> turning on interior heater with fan brings temp down
> radiator is brand new ( 6 months )
> ( i have only seen water pumps fail by leaking and screeching )
>
> What might it be ?   How can I test ?
> 99guspuppet

The easiest and cheapest thing to check is the thermostat. I believe that
the heater takes its feed from before the thermostat.  Pretty easy thing
to change on the Miata, too.

Matt Bennett
Just outside of Austin, TX
30.51,-97.91

The views I express are my own, not that of my employer, a large
multinational corporation that you are familiar with.
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