temp gauge not working???????
 

I have a 69 gmc 3/4 ton that I have retrofitted tbi injection on the stock 350...out of the blue temp gauge stops working and is pegged to the cold side....I grounded the wire going to the temp sending unit and the gauge pegged to the hot so I thought install new sending unit would fix my problem but the gauge is still pegged to the cold side...only thing I am wandering is the heater hose return hose goes to the pump instead of the radiator like on the late model I got my tbi from...I also changed thermostat thinking it might be stuck open and not letting the engine warm up...any ideas and I very open to suggestions...

Re: temp gauge not working???????
 

What year is the sending unit you are using in the engine?

Re: temp gauge not working???????
 

stock 69 sending unit

Re: temp gauge not working???????
 

Replace the wire from the sending unit to the gauge. Might be broken. Also check the connection at the sending unit and make sure it's really clean. That was the problem on mine.
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Re: temp gauge not working???????
 

[QUOTE=coldgin;6090220]I have a 69 gmc 3/4 ton that I have retrofitted tbi injection on the stock 350...out of the blue temp gauge stops working and is pegged to the cold side....I grounded the wire going to the temp sending unit and the gauge pegged to the hot so I thought install new sending unit would fix my problem but the gauge is still pegged to the cold side...only thing I am wandering is the heater hose return hose goes to the pump instead of the radiator like on the late model I got my tbi from...I also changed thermostat thinking it might be stuck open and not letting the engine warm up...any ideas and I very open to suggestions...[/QUOTE

Has the gauge worked since you changed to TBI?

Grounding the sending unit wire shows two things A. the gauge is responding as it should and B. the wire is not open to the gauge.
This leaves the sending unit as the problem. Especially since the gauge was working before.

When you changed to TBI did you mount the gauge anywhere besides the left cylinder head and did you uses any sealer on the sender threads?

The heater hose does not have anything to do with the temperature gauge. You could have the heater hose disconnected and plugged and the gauge would still work.

Re: temp gauge not working???????
 

I did use sealer on the threads...do you think it is causing a bad ground?

Re: temp gauge not working???????
 

vette the sending unit is still in the left head...never moved it and was the original sending unit...

Re: temp gauge not working???????
 

check for continuity between the sender body and the cylinder head, if you get infinity ohms then you're not getting a ground. There is a sealant that is electrically conductive, but I don't know the brand name offhand. If you don't have an ohm meter then just take the wire off the sender and touch the sender body and watch for the gauge to go hot. Key on of course.

Re: temp gauge not working???????
 

I was driving the truck the other day and I noticed when I turned the key on the needle would fall all the way past the "c"....when I turn the key off the needle would come right up to the edge of the "c"....I am thinking it was doing this with the old sending unit...beginning to think it is the gauge...anything else I need to check?