Join Date: Aug 1999
Location: Ontario, Canada
I run a mechanical gauge in my 68, 350,
It runs a high temperature, during the summer months, I worry about the Temp all the time,
The way you explain that the gauge drops to 160 -180 suddenly, is when the thermostat opens and allows the coolant to flow through the radiator, If this has happened with two different thermostats, and the gauge reacts the same then I would assume that the engine is fine and look at your gauge.
In my 68 I run the mechanical gauge in the water plug right under the thermostat housing, The tube runs along the top of the intake manifold, under the distributor and through the firewall, It is this routing I believe that causes the gauge in my car to run such a high temp, 220 -230, No thermostat, just a restrictor ring, I also use the original temp light plugged into the water jacket between # 1 & 3 plugs, Funny how the gauge reads so high and the light does not flicker or come on, I have concluded that the temp reading of the gauge is high but the actual engine temp runs 20 -30 degrees less than the gauge reading, It could be possible that the tube is picking up heat from the manifold, near the carb and affecting the gauge reading.
I think that if I were to change the location and routing of the tube away from the engine then the gauge may read accurate.
What water jacket plug are you useing??
Where is the tube routed??
Can any body else offer comments???