1994 Chevy full size pickup with temp gauge issue

[zamimj222]

I am looking for some help. I have a 1994 Chevy K3500 Cheyenne with a 5.7L. approx 64,000 miles. Mileage is correct. It used to be a plow truck at work. Problem I am having is temp gauge on the dash reads approx 150 degrees after being warmed up and when I plug in the OBD1 tool it says the engine is around 195 degrees. I replaced the stat as I had issues getting the engine to warm up like it should. Found the stat was stuck open. Replaced the sensor between #1 and #3 cylinders after grounding the wire off the sensor and the temp gauge pegged. Looking for some help to fix this. The old sensor was reading low too. Guess I am down to wiring issue.....

 

[Mooseman]

I would imagine it would be. Look on the internet for what resistances that should translate to what temperature. Could be the gauge itself.

 

[mrrsm]

If you can Google some images of the Coolant Sensor Locations... the 1994 GM 1500 5.7L Engine appears to have TWO of them... one on the Driver's Side Cylinder Head and one mounted close to the Intake Manifold/Coolant Hose Elbow area on the front Passenger Side of the motor. It seems possible that if they have Two Different Part Numbers and Behaviors that could be threaded in at the WRONG locations and thereby... provide incorrect read-outs on the Dash Gauge.

 

[zamimj222]

I would imagine it would be. Look on the internet for what resistances that should translate to what temperature. Could be the gauge itself.

I have been searching the internet for 3 days before posting. For some reason this seems to be a mystery of why this isn't posted anywhere. Gauge seems to work accurately. If I install a 46 ohm resistor, it goes right to 260. But then again, I am kind of guessing that the resistance matches up with tthe temperature...

 

[zamimj222]

If you can Google some images of the Coolant Sensor Locations... the 1994 GM 1500 5.7L Engine appears to have TWO of them... one on the Driver's Side Cylinder Head and one mounted close to the Intake Manifold/Coolant Hose Elbow area on the front Passenger Side of the motor. It seems possible that if they have Two Different Part Numbers and Behaviors that could be threaded in at the WRONG locations and thereby... provide incorrect read-outs on the Dash Gauge.

When I went to the parts store, they do have both sensors. The one by the thermostat housing is used by the computer in the truck and the scan tool. The one between cylinders 1 & 3 goes to the gauge. I replaced the correct one. Just wanted a reliable gauge to make sure I don't over heat or something else is going on. I'll keep searching. Maybe I will install a mechanical gauge and see if that is better.

 

[Mooseman]

Had a look in GM SI and it has nothing for 1994 but did find this for 1996:

The engine coolant temperature sensor is a thermistor (a resistor which changes value based on the temperature) mounted in the engine coolant passage. A low coolant temperature produces a high resistance (100,000 ohms at -40°C/-40°F) while a high temperature causes a low resistance (70 ohms at 130°C/266°F).

So your check seems to be close.

Here's there chart for the 02 TB. Seems to be the same for 266F (7 ohms difference is negligible).