91 SD L98

So here is my situation. My fans wont come on. The ECM is programmed to ground the relay at 222 degrees. Now the engine temp guage is going above 222 but the Coolant Temp Sensor is only reading around 190 at that point.

Could I just have an air pocket by the CTS or do you think it is a bad sensor?

Since the CTS isnt reading 222 the fans wont come on.

 

The temp gauge and its sensor are sometimes not that accurate. Have you measured the actual temp with something more accurate?

 

well icould put a pyrometer on it, but where would be the best place to take that reading?

 

u can try the thermo housing neck. those stock gauges are not very accurate.

 

Upper rad hose or use a multimeter and measure the resistance of the coolant temp sensor (below the t-stat).

 

The gauge sender is also in the head, between two exhaust ports, a considerably hotter part of the motor. You can expect a bit of disparity between the temperature gauge and ECM reading.

 

how are u measuring the temp that the cts is seeing? a scanner,laptop?

 

snap on scanner

 

What parts of the sensor do I hook my multimeter to? Unhooked sensor to ground? Unhooked sensor to sensor wire lead?

 

If the CTS is in a considerably cooler spot of the motor than the Temperature gauge sending unit how about changing positions. Put the CTS in the Temperature gauge sensor location and visa versa?

 

I don't think you'd want the ECM seeing the engine temp as higher than what it's actually running, just for the sake of the gauge to read lower.