1991 ranger temp gauge not working

[91supercab]

First off its a 91 ranger with a 3.0 v6. I just changed the thermostat and flushed the radiator because i was have low heat problems and the temp gauge never leaves Cold. Now the truck has better heat but the gauge still doesn't move. I haven't noticed it moving at all over the last couple weeks. It used to move a little but it never would get up to where i thought should be normal. I pulled the plug and ran a jumper wire and still nothing. Weird thing is ...it actually causes the check engine light to come on when i jump it. I was going to just take the easy route out and install and aftermarket temp gauge and call it done..but now i'm worried about having the check engine light if i unplug it. Did the light come on just because i jumped it?? I should have checked it with it just unplugged with no jumper but i didn't.

I also checked it with a test light and it barely lit up...by barely i mean with no lights on in the dark ...i could barely see it. That leads me to believe the wiring or the gauge is faulty. I really would rather just install an aftermarket gauge and call it done. If anyone knows if i can unplug that temp sensor and just install an aftermarket one let me know. This is just my daily beater and not really looking to tear the dash apart to make it look factory.

 

[martin]

There are two temp sensors, one for the gauge (one wire) and one for the computer (two wires). A bad connection at the sensor is a common problem.

 

[91supercab]

Ok well i must have just found the 2 wire one then. It was right next to the thermostat and inlet neck. Just to the right (if your looking straight at it. Where is the gauge sensor at then?

 

[RonD]

The 2 wire sensor is for the computer, it's often called the ECT sensor(engine coolant temp), it's connector faces up towards the hood.
Since its part of the computer system the CEL came on when you shorted it.
This sensor is used as the "choke" on EFI systems, cold temp causes a run rich setting, then leans out mixture as sensor warms up.
Reduced mileage could mean this sensor is failing.

Just below the T-stat housing and facing forward toward the rad is the 1 wire "water temp indicator" sensor, for the gauge.
It should be next to the screw in elbow fitting for the heater hose, if memory serves.


This is for pretty much any 1 wire temp gauge:
To test the temp gauge, turn on key, unplug the 1 wire on this sensor, jump that wire to any ground, gauge should go to full hot.
If it does then wire and gauge are good, replace sensor.
If it doesn't then either wire or gauge is bad, sensor might be ok.


These are resistance sensors, as temp rises resistance is less so gauge goes up, grounding the wire is 0 resistance which maxes out the gauge, no it won't hurt it.
Because of the way these sensors, and other 1 wire sensors work, don't use tefon tape to seal them, you can put sealant on the upper threads but leave the lower threads bare for a good ground.