Testing Temp Gage? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Als454 · 12-10-2005, 04:13 PM

Is there a way to test my temp gage to be sure it is good? The dash is out of the truck now.

matt67350 · 12-10-2005, 05:11 PM

Go to www.madelectrical.com
Under there Work Shop Tips, they walk you through testing a temp gauge.

Als454 · 12-10-2005, 07:14 PM

I guess I'm looking for something a little more specific to out trucks. I know my engine is not running hot but when the dash was in the gage pegged, I took a meter to the sending unit and it appears to be working. I took another gage that I had on the shelf and jumpered some wires to it and got the same result. What I'm asking is there some way with gage out to test it. I what to eliminate the possiblity of a bad gage.

**pjmoreland** · 12-10-2005, 07:37 PM

The needle may have pegged because the green wire that connects to the sender was shorted to ground somewhere.

There are two terminals on the back of the temperature gauge. One connects to 12 volts, and the other connects to the sending unit (green wire). Take a look at the connector that plugs into the back of the gauge panel and find where the green wire is. Follow the copper trace on the printed circuit board to your temperature gauge to determine which terminal the green wire connects to. Connect 12 volts to the other terminal. Connect ground to the green wire terminal momentarily, and the gauge should peg.

The sending unit adds somewhere in the range of 500 Ohms of resistance to the ground circuit (green wire) of the temperature gauge. The resistance drops off as the engine heats up. You could try connecting the sending unit between the green wire terminal of the gauge and ground. You'd have to add heat to the sending unit to see the needle move. You could try as rick980 suggested and place it in a pot of water on your stove. You'll have to be very careful not to let the sending unit or wires short out on the pot though. Sounds risky. You might be able to heat the sending unit up with a torch or something. Still sounds risky. If you could get your hands on a variable resistor that had the appropriate range, you could connect it in place of the sending unit. I have no idea what resistance corresponds to what reading on the gauge though. Hopefully someone else has an idea.

Also make sure your sender is for a gauge panel with gauges, not warning lights. The sender should look like this:

12-10-2005, 04:13 PM	#1
Als454 Senior Member Join Date: Jan 2002 Location: Vienna, Ohio, USA Posts: 259	Testing Temp Gage? Is there a way to test my temp gage to be sure it is good? The dash is out of the truck now. __________________ 72 Chevy A/C P/B P/S Tilt 454 Engine 400 TCI Trans C30 Frame C10 Suspension Short Wheel Base (Dually)

12-10-2005, 05:11 PM	#2
matt67350 Registered User Join Date: May 2001 Location: Benbrook, TX Posts: 1,060	Re: Testing Temp Gage? Go to www.madelectrical.com Under there Work Shop Tips, they walk you through testing a temp gauge. __________________ 69 swb stepside, rebuild and upgrade in progress Last edited by matt67350; 12-10-2005 at 05:13 PM.

12-10-2005, 07:14 PM	#3
Als454 Senior Member Join Date: Jan 2002 Location: Vienna, Ohio, USA Posts: 259	Re: Testing Temp Gage? I guess I'm looking for something a little more specific to out trucks. I know my engine is not running hot but when the dash was in the gage pegged, I took a meter to the sending unit and it appears to be working. I took another gage that I had on the shelf and jumpered some wires to it and got the same result. What I'm asking is there some way with gage out to test it. I what to eliminate the possiblity of a bad gage. __________________ 72 Chevy A/C P/B P/S Tilt 454 Engine 400 TCI Trans C30 Frame C10 Suspension Short Wheel Base (Dually)

12-10-2005, 07:37 PM	#4
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,981	Re: Testing Temp Gage? The needle may have pegged because the green wire that connects to the sender was shorted to ground somewhere. There are two terminals on the back of the temperature gauge. One connects to 12 volts, and the other connects to the sending unit (green wire). Take a look at the connector that plugs into the back of the gauge panel and find where the green wire is. Follow the copper trace on the printed circuit board to your temperature gauge to determine which terminal the green wire connects to. Connect 12 volts to the other terminal. Connect ground to the green wire terminal momentarily, and the gauge should peg. The sending unit adds somewhere in the range of 500 Ohms of resistance to the ground circuit (green wire) of the temperature gauge. The resistance drops off as the engine heats up. You could try connecting the sending unit between the green wire terminal of the gauge and ground. You'd have to add heat to the sending unit to see the needle move. You could try as rick980 suggested and place it in a pot of water on your stove. You'll have to be very careful not to let the sending unit or wires short out on the pot though. Sounds risky. You might be able to heat the sending unit up with a torch or something. Still sounds risky. If you could get your hands on a variable resistor that had the appropriate range, you could connect it in place of the sending unit. I have no idea what resistance corresponds to what reading on the gauge though. Hopefully someone else has an idea. Also make sure your sender is for a gauge panel with gauges, not warning lights. The sender should look like this: Attached Images Last edited by pjmoreland; 12-10-2005 at 07:38 PM.



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