Help with thermostat theory

[dlampe]

Does the thermostat set the minimum operating temperature for the engine. If the engine runs at 195 on a hot day, would a 160, 180 or 190 thermostat make a difference? The reason I ask is I replace my intake gaskets and in the process noticed that I had the wrong thermostat based on diameter. I was running a 170 but the car usually ran around 190 to 195 without any problems. The only thermostat they had at the parts store that was the right size was a 195. So will my car run hotter as a result of the higher thermostat temp? I don't think so but the minimum temp will now be 195 instead of 170.

What do you think?

[Barnsnake]

The thermostat theoretically sets the minimum operating temperature. When the coolant at the thermostat reaches the specified temperature (195 in this case) it opens. The indicated temperature may continue to rise slightly before the cooled coolant comes back from the radiator to the temp sender. The thermostat will close at a temperature below the rated temp (maybe 185), so the indicated temperature may temporarily drop below the thermostat temp.

If the cooling system is up to the task, the engine temperature, after warm up, should cycle at or near the thermostat temp. If it is regularly going above the thermostat temp, there are a number of possibilities.

1. If it only occurs at low vehicle speeds, the thermal switch for the fan may be at a higher temperature than the thermostat. In that case, the fan switch is controlling the minimum temperature until vehicle speed increases.

2. If it occurs at moderate speeds, or low speeds with the fan on continuously, the cooling system may be marginal for the task. This could be radiator size, water pump speed, fan capability, shrouding, or a combination thereof.

3. If it occurs at all times, the temperature gauge may not be refecting the actual engine temperature.