94 G30 overheated, now temp gauge won't work

My 94 G30 (350 engine) work van overheated two days ago (I was not driving). I went to rescue them and found lower rad hose burst and freeze plug leaking. System was full of crap. Fixed hose and plug but on return trip the temp gauge did not work - reading low scale. After 30 minutes the SES came on. I guessed it was still getting hot and that the sensor is still telling the computer the temperature, but not sending the signal to the dash gauge. I let it cool down and then finished the trip.

Next day I flushed it and determined the thermostat was stuck closed. Replaced same and is seems to be running cooler. Dash gauge still does not work. Pulled temp sensor jack (2wires) located next to stat on top of block and SES came on immediately. I think this means that the sensor is sending good signal to the computer but not to the dash.

When it overheated I'm told the temp gauge needle pinned on redline-hot but this shoudn't break it. But JIC I pulled the instrument cluster and tested the temp gauge. No voltage on the "S" terminal. Jumped ingnition (+) to "S" and needle indicated fine.

Is there a second sensor just for the dash?

If the dash gauge signal comes from the computer, why would it go bad just because it overheated?

Any suggestions?

I own a 93 G20 Van and have had the same problem on my 350ci/5.7l V8. The sending unit for the temp. guage is located on the drivers side middle of the engine just below exhaust manifold. It will be a single wire and if you remove the wire and ground it with the with ignition on but engine not running the temp guage will go to hot.
I have gotten lots at the wreckers over the years because they are worth $25.00 at most after market stores.

Hope this helps

Thanks for the info. I will look tomorrow. Sounds like you're saying there is a separate sending unit for the gauge.

I saw a single wire coming out of the same harness as the sensor next to the stat, but I did not trace it. I thought is was going to the oil pressure sensor.

Yes, the temp guage has its own sending unit and the single wire goes directly to the guage. I have used sending units from 350/305 engines from 1990 to 1996 and have found they all work great keeping the needle around the middle of the guage at normal operating temp. If I go to the wreckers I look for a van, 305/350, with temp. guage not a dummy light. The sending unit is in the same spot on everyone. The wiring harness plug may be different but I usually take the sending unit and plug from the wreckers and splice the wire to my van.
I am not a mechanic but I do know a bit about electronics and allways check the wiring schematic before substititing parts like this. I would never recommend replacing any component with anything other than the original if it was connected to the car's computer, for example. In this case the schamatic shows the sending unit wired directly to the guage, a simple curcit with the sending unit used as a varaible resister.

You are exactly right. I grounded the wire and the guage went to high scale. It's definately a bad sending unit. I"ll start looking for one this weekend. Thanks a lot for your help.

I don't have any diagrams for this van so I was having trouble figuring it out by myself.