Oldsmobile, Silhouette, 1990, Temp guage not working.?

Question

Repost as I botched first question, sorry:

1990 Olds, Temp gauge reads 1/4 of scale, with 1/2 way being about normal. I changed Thermostat with new one.
Plenty of heat so that is working. So I changed Temp. Sensor on engine block (2-wire electrical clip) on top. Made no difference...

as the engine heats up the gauge rises to just above 1/4 of mark on gauge and stops, then as the Thermostat opens, the needle on guage will drop to 1/4 scale mark.

I will run a new gauge, line etc.. if I can't figure this out but hoping something simple... as for changing gauge from one from junk yard, ... I can take a look behind dash and see what that would take, not the most friendly environment up in there.

Oh.. this Mini-van has 256,700 miles, never had engine cracked open and one solenoid on tranny changed... so it has been a keeper with just routine maint.. Just about on last leg but will runner till she drops...

Thanks for prior posts, sorry for botched first question.

Your right, the two wire feeds the computer.
I found the Sensor with the single wire on the back side of the engine and un-connected and needle didn't function so figure I would replace since I found it hidding back there, however this item is Dealer item only, no one has it at parts store.

So will take chance and just replace, I guess I could throw a resistance across it or possibly check for continuity or something but don't have chiltons to give me specs.. so might as well just replace and see what happens...

Hangtroj... yea.. I re-read your message and finaly it sunk in. I grounded single wire and the needle pegged too the top so confirmed gauge is O.K. and sensor is bad...

thx for the advice.. exactly what I needed.... and agree... how simple it was... just had to think about it for a minute...

Answer 1

Does the engine only have one temp sensor? Some engines will have one for the ECU, and another for the dash temp guage. Typically, the one for the dash is a one wire sensor, at least in my experiences with such. One side of the guage has constant 12vdc, and the sensor provides the path to ground, depending on the amount of heat it senses.

The dash guage seems to be working, but a truer test would be hooking a pot to it and seeing if you can get full swing, from cold to hot, by varying the resistance of the pot.

Answer 2

Simple circuit, simple diagnostics. Locate the proper temp. sensor on the motor as there are two. One for the PCM temp. input and one for the driver's guage. The PCM has two wires going to it and the guage has one. All you have to do is unplug the guage from the sensor, turn on the ignition and look at the guage. It should either be at cold or over the hot mark. Now ground the guage wire to the block being sure that it is grounded and re-inspect the guage reading. It should be opposite of the open. If it does both of these functions, the wiring and the guage are responding. Usually we would install a new sensor into the block to see if that is the problem. Since you have already done this and are sure it is not the problem, you have a faulty dash guage. I think these require a complete dash assembly which is pricey. Good luck.

Answer 3

Being that I am now not a technician and I am now not capable to diagnose your quandary over the web, I might propose contacting your regional trader for extra help. They will have to be capable to factor you within the correct path. If you've extra questions, please think unfastened to touch me by way of e-mail. Thank you. Tricia, GM Customer Service.