Temp gauge was running around 150 and I hadn't looked at the thermostat since I bought the car so I decided to install a new STANT 195 for winter. Installed the new 195 and the gauge was still reading 150. Thought I must have a bad engine coolant sensor so I head on down to the parts counter and grab a new one. Installed new sensor and gauge still shows 150.

Tonight I removed radiator cap and let the engine idle about 10 minutes to warm everything up and the electric fans engage and run about 45 seconds and shortly after the fans start I can look in the radiator and see that the thermostat has opened and water is pumping through the core. Outside air temp is about 50 degrees. Thermostat cycles normally. Gauge in dash reads 145-150 as the 195 degree thermostat opens and closes.

I guess the next step is to get a scan tool on it and see if the sensor is sending a reasonable value to the PCM and try to determine if I have a bogus gauge in the dash. Oil pres, fuel gauge, volt meter all seem good. What else should I look for?

Tumbleweed

chances are your gauge is reading low.

On the gauge clusters with boost (only pre 96 that I know of) the three gauges to the left would mess up and it was an easy replace a small circuit board in the cluster for those fix.

I did it, Jimmyfloyd did it, and I think Nate did it.

where can we get the board?

If my coolant temp sensor really is sending a value of 145 to the PCM, wouldn't I get a "check engine" light?

I am guessing the sensor is good and the problem is up in the dash. The scan tool should tell the story.

Tumbleweed

I am guess it is the gauge to ,but Ino you wouldn't get check engine light for low temp. That would mean ever time u start the car the engine light would come on.

I'm fairly sure that it would though. Isn't that why we can't run 160'*...one of the many reasons we can't use them.

I have checked the haynes codes for obd 1 and obd 2 both have Engine Coolant temp sensor circuit low input so I stand corrected

You probably have a 3 pin temp sending unit mounted under the thermostat housing. This 3 pin temp sending unit has two temp sensors inside with two of the wires going to the one that tells the PCM engine temp. The other sensor has one leg grounded to the case and connects to the third wire on the sending unit plug. This is why the sending unit has to have good contact with the lower intake manifold to function properly.
The sensor with one wire is for the temp gauge in the dash panel.

Both sensors read about 2700 ohms at 77*F and about 240 ohms at 195*F.
So if you disconnect the sending unit plug and connect a 1000 ohm potentiometer to ground you can test the dash gauge. Someone with a service manual for your car should have the temp sending unit wiring showing what color wire goes to the gauge sensor.

I haven't done nothiing yet.....my coolant temp is actually some what acurate untill 200*