Help with thermostat theory

[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.