Temp gage reading wrong temp.

[ram1220]

Try removing the wire that connects to the sensor by the thermostat. My 90 Sierra temp gauge does this from time to time. I have to clean the connector that attaches to the sensor. Place it back on the sensor after cleaning and your temp gauge should work. Also when you changed the thermostat are you sure you got all of the air out of the system? If not try "burping" the radiator.

 

[evilunclegrimace]

Try removing the wire that connects to the sensor by the thermostat. My 90 Sierra temp gauge does this from time to time. I have to clean the connector that attaches to the sensor. Place it back on the sensor after cleaning and your temp gauge should work. Also when you changed the thermostat are you sure you got all of the air out of the system? If not try "burping" the radiator.

The temp gauge is controlled by the SENDER that is in the left cylinder head. The ECM reads the coolant temp from the SENSOR that is in the intake manifold.

 

[ram1220]

When you say left do you mean passenger's side or driver's side? Because I know that if I remove the wire attached to what looks like a sensor on the driver's side my temp gauge will drop to about 100. After it's cleaned and the wire is reconnected my temp gauge reads like it should. Before I clean it my temp gauge reads from 0 to 100. It might not be the sensor that you are talking about but it definitely looks like a sensor screwed into my engine on the driver's side. I mentioned this as something else the OP could check. I can try and get a picture of it if it might help. Oh and I tried quoting evilunclegrimace's latest post as this is directed towards him but the forum would not attach the quote no matter what I did.

 

[evilunclegrimace]

When you say left do you mean passenger's side or driver's side? Because I know that if I remove the wire attached to what looks like a sensor on the driver's side my temp gauge will drop to about 100. After it's cleaned and the wire is reconnected my temp gauge reads like it should. Before I clean it my temp gauge reads from 0 to 100. It might not be the sensor that you are talking about but it definitely looks like a sensor screwed into my engine on the driver's side. I mentioned this as something else the OP could check. I can try and get a picture of it if it might help. Oh and I tried quoting evilunclegrimace's latest post as this is directed towards him but the forum would not attach the quote no matter what I did.

The left side is ALWAYS the drivers side when referring to a vehicle. And yes you have the correct position for the sender. It is common for the connection to corrode over time. An easy fix is to clean the sender terminal and the wire connector very well and spray a little battery terminal protectant on it to help prevent corrosion in the future.

 

[retorq]

Is it possible you put in a failsafe thermostat and it's now stuck open? That could behave the way you described.

 

[Lonnie White]

Aside from taking forever to get heat, my 94 is doing the exact same thing.
If you figure it out before I do let me know

 

[evilunclegrimace]

One slim possibility is that the water pump impeller is slipping on the shaft, it does not happen often but it does happen. Drain a couple of quarts out of a cold engine and start the truck and watch the coolant return line at the radiator fill neck to see if the coolant is flowing a fairly high rate.

 

[Blackwater]

The temp gauge is controlled by the SENDER that is in the left cylinder head. The ECM reads the coolant temp from the SENSOR that is in the intake manifold.

I have replaced both sending units in 2011 but no change. I haven't worried about it since it never gets hot. Now the pump, I'm not sure of it. I may just do nothing till I get the modified Vortec Max installed.

 

[superdave]

Thermostat stuck open is the likely suspect when an engine is struggling to get up to operating temp. Still, a temp gun is the easiest way to diagnose these things.