Temp. sending unit on 2002 with 3.8

In the last year, I have done all the usual things to my GP. UIM, LIM, plugs and wires. The car runs great. My question is the gas mileage. My temp gauge hardly ever goes above 180. I put a new stat in when I changed the gaskets, but I think it was doing the same before that. I put a 195 degree stat in. Does the computer take the temp reading from the sending unit. If the computer thinks the car is running cold, would that not affect my MPG. Just trying to figure this out. When the car was new I easily got 28 MPG, now only get 22-24. Just wondering if changing the sending unit would help mileage?

Short answer: MAYBE. The temp is calculated in the fuel MAP and thus affects mileage. But the temp you see on your gauge may not be the temp seen at the PCM. The sensor has a dual output. One goes to the instrument cluster for your gauge, the other to the PCM for the fuel MAP. If you hook up a scanner, the temperature you read is from the PCM input, not the gauge. They should be the same, but obviously will vary. I can scan my temperature, but I am still trying to troubleshoot why I don't have a signal on my gauge. Good Luck! Don't change the sensor unless you are getting significantly different readings on the gauge than you are the scanner, if you are sure the gauge is working properly.

ktmccrary has given a good option, use a live-data capable scanner and check the temperature the PCM sees and compare it to the temp on the dashboard, if you see any difference then replace the sensor.

If the PCM does not detects the correct temperature (either because of a bad ECT or no thermostat) won't go into closed loop mode AFFECTING your fuel economy.

Finally you can also check the ECT sensor for resistance in order to see if it's good or bad.

Best regards,

Oscar.