I lost my sending unit on my 1990 5.0L and after I replaced the unit my gauge now reads 2/3rds of the scale. Motor seems to be about the same temperature as before unit failure and the gauge was at bottom 1/3 of scale. Are the thermocouples (sending units) calibrated for the gauges? Also, I grounded the sending unit temporarily to make sure my panel gauge was working I did not leave it grounded long enough to even reach full scale so I do not think I damaged the gauge.

 

what do u mean by not leaving it grounded long enough to even reach full scale?

Like, for the gauge to peg out? It should peg out right as the wire is grounded, you ground the sending unit wire and the gauge needle pegs to hot. Then you know the gauge is working. Is this what you did?

 

Thanks for the reply,

Yes, I basically let it go full scale but I did not hold for any length of time. Should I disconnect and allow to peg longer? I thought if it moved at all it was probably ok.

 

If it swings when you ground it it is working. My only though is make sure you have the right sender for you truck.

 

When I did it, I left the key off, grounded the wire to the sending unit, turned the key on and it went right over to Hot....it should be within a few seconds that the needle arrives to hot.

 

If you have a VOM, you can check the resistance at different temperatures. Attach the leads to the sender and place it in a pan of water. Then place a thermometer in the water. Here are a couple of readings at higher temps. 104=1459ohm, 140=667ohm, 176=332ohm, 212=177ohm. Remember the temp of the water inside your engine gets hotter than 212, but you can't test in an open vessel because boiling water won't get hotter than 212. If your readings are significantly different than these, then you have the wrong sender. Good luck.

 

Thanks again,
I will try my VOM as soon as I get in from fishing on Sunday.