| oldmarine |
07-16-2020 04:10 PM |
Disconnecting the temp sensor hasn't told you anything about whether it is working properly or not. The resistance through the sensor tells the ECM what the coolant temperature is, but if no signal is the same as low temperature, the ECM may still think the engine is not warm. Do you have a CEL or any codes?
The ECM should turn the cooling fan on (with AC off) any time the coolant temperature exceeds 223 degrees Fahrenheit (the boiling point of 50/50 coolant with no pressure in the cooling system) and your speed is under 70 mph. If the cooling fan is coming on when the AC is turned on, the cooling fan relay and the fan motor itself are working properly, and the ECM is providing the necessary ground for the circuit. So the ECM not turning the fan on when the engine reaches an overheating condition is probably because the ECM does not recognize that the engine is overheating. A temperature sensor is less than $15 dollars - cheap troubleshooting.
The other item to check is the pressure cap on the surge tank. As stated above, the fan should come on when coolant temperature reaches the boiling point of 50/50 coolant with NO pressure on the cooling system. If you have pure water, or less than a 50/50 mixture, the boiling point comes down, to 212 degrees for pure water. So the system would start to overheat (boil) at a lower temperature. At system operating pressure of 12 psi, the boiling point of 50/50 coolant is 259 degrees, so no overheating would occur if the fan comes on at 223 degrees. Check the pressure cap to ensure it holds the proper system pressure.
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