With my ScanTool connected the CTS reads in the 180-190 range during regular driving(30-45mph) and from 200-207 on the expressway(70-80mph). The stock gauge reads about 180-190 most the time, but my AutoMeter gauge(fitted from the water pump) reads 175-180 most the time. You can read it go from just over 180 and seemingly like the stat opening/closing, once it goes above 180 it drops to 175-177 ish, etc.

What gives? I know stock gauges are not always accurate and trust the ScanTool, but the AutoMeter I normally trusted until now.

I have a 180 stat, 87' TPI setup thats mostly stock besides headers/catback fitted on my 87' Monte. Running the TPI dual fans, wired so one fan runs constantly(by accident but better than not working). Modine 951 f-body alum. radiator. I ideally wanted it to turn on automatically, have a Jet switch in the passenger side head hooked up and all, but oh well thats another story. Car runs fine, only a sporadic EGR code(with new GM valve/switch). Not rich or lean, closed loops just fine, etc.

Any reasons why the CTS reads 20 degrees or more higher than the other gauges? 200-207 might not be that bad I guess but I wouldn't mind it being a bit cooler. The CTS is a new Wells unit from Autozone put in last year as well. Not sure what else to add.

Anyone else have this situation? Tips or answers? TIA!

 

The reason is the location. Your autometer gauge is in the water pump that is in the front of the engine recieving the cool air first, and closer to your radiatior, recieving the already cooled coolant, your CTS is in the passanger side back of the head between your exhaust manifolds. Of coarse there is going to be a bit of a difference in temperature becuase the heat is being created right where the CTS is. Also, your CTS is just as acurate as your autometer gauge, your coolant sending unit (drivers side front of head) is just as accurate too, but the gauge itself is not calibrated as accurately as your autometer gauge is. According to your description, everything is perfectly normal. Temp changes are going to fluctuate especially at the water pump becuase as soon as the thermostat opens you are having two different temperatures of coolant changing spots. Hope this clears up your question.

 

Thanks for the reply. I'm not too worried since the temperature wasn't that hot, but figured it should be a bit closer to the other gauges I guess. Another thing is the CTS is located on the front of the intake, not in the head. The fan switch is in the passenger side head...