Hello, Fred... I hope this helps you AND fellow Vette owners...
Your answer might not rest with the thermostat or temperature gague. It may rest with your temperature sending unit.
My 1971 350 always ran hot since I bought the car until I personally replaced the wiring harnesses from 'Lectric Limited, throughout the car. The engine compartment harness temperature sending connector on the replacement harness would NOT mate with the block's sending unit. My initial thought was that the sending unit was replaced with a newer unit and they started coming with new connector style. But, after spending the money and time replacing the harness, I could not bring myself to cut the clip and splice a 'modern' connector to keep the install moving along. Instead, I did a bit of research and found that the appropriate sending unit with the proper tab is still being made. I bought it, installed it and took note of operating temperature on the cluster gague...IT WAS NOW RUNNING NORMAL!!!
It really matters using the right components. It seems that temperature sending units are CALIBRATED to certain gague designs. In this case, the auto stores list suitable substitutes based on thread size, but not thermo-electrical calibration.
Consider checking calibration compatability between your sending unit and the cluster gague.
Tony
