Interesting results today... I drove the car to work (30+ miles each way, with mountains, highways, and slow level driving), and it hit a peak of about 215 degrees, and was hot pretty much everywhere (at idle, at cruise, on the highway at 80 MPH, etc...), so I stopped at the local AutoZone on the way home and bought a new Robert Shaw thermostat.
I pulled the old t-stat out, and stuck both of them in a pot of water on the stove. Both were rated at 160 degrees, and both opened more or less exactly the same time. The only difference was that the new Shaw thermostat opened much *LESS* than the old one, and has a slightly smaller orifice.
Stuck the new t-stat in, and took the car for a testdrive. Never got above 190 (even with my wife beating on it
). In nearly identical weather and driving conditions last night it was running at 205. I guess there might be some truth to the theory that you have to slow the flow through the radiator to give the heat time to disperse.
I'm pleased with my new $4.95 thermostat. Slightly less pleased with my new $300+ electric fan setup, but hopefully it'll earn its keep at the dragstrip on Saturday.