Temp Gauge

[bronyaur]

'95 Suburban 5.7L K1500

 

Temp gauge slugglishly rises from cold to about halfway between 100 and 210 but never goes any higher. It might move a little lower on occasion, but that's about it. I used to be able to watch it go straight from cold to about 210, then drop fairly rapidly and settle in between 195 and 210 depending on the driving conditions.

 

The first thing I replaced was the temp sending unit on the side of the head. Next I replaced the thermostat. During that process I noticed the top of the engine coolant temperature sensor was broken, so I replaced that as well. The problem persists, and has not set a code.

 

The last thing in the equation I can think of is the gauge. Any suggestions?

[Mikeee]

Somewhere there is a diagnostic for the temp gauge itself. It is in the official GM service manual.

 

I had a similar problem on wifeys 98 Lumina. I chased/replaced a bunch of things and still had the problem. The dash gauge was tested using a set value resistor for 100* and one for 260*. The gauge was reading wrong. It is in the GM service manual. Now we just ignore the gauge.

[bronyaur]

Thanks for the tip. Based on your response, I did some research and found that GM suggests the use of a Kent Moore J33431-B Signal generator. I don't have one, or access to one, and they look to be pretty expensive - not the kind of thing a DIY mechanic generally has.

 

Apparently 1305 ohms should cause the gauge to read 100 degrees, and 49.5 ohms should cause the gauge to read 260 degrees. Anyone have any suggestions on how to generate that exact resistance without an expensive tool?

[Mikeee]

Got my variable resistor at Radio Shack.

Maybe $2.

I already had an ohm meter.

Those are at Walmart for cheap $.

[redstreetracer36]

Fluke 87 meter..fairly cheap at walmart

[Godti]

Got my variable resistor at Radio Shack.

Maybe $2.

I already had an ohm meter.

Those are at Walmart for cheap $.

 

So how do you hook it into test the gauge??

[bronyaur]

Here's how I'm envisioning this process: pull the connector from the sending unit. The connector has two leads connected to wires. Connect a wire from one lead to one side of a variable resistor such as a rheostat. Connect the other side of the rheostat to the second lead in the connector. Connect an ohm meter - one lead to each side of the rheostat. Turn the ignition key to the "on" position. Adjust the rheostat until the ohm meter reads 1305 ohms. Check the temp gauge - it should read 100 degrees. Adjust the rheostat until the ohm meter shows 49.5 ohms. The temp gauge should read 260 degrees. Does this sound right?

 

I already have a decent multi-meter, but coming up with the right rheostat may take some research. A friend suggested using a really long steel spring that has been slightly sprung (so the coils don't touch). Attach a wire to one end, and the other can be moved anywhere along the spring. The greater the distance from the first wire, the greater the resistance. With an ohm meter attached to each lead in the connector, just move one wire either direction until the desired resistance is shown on the ohm meter. That sounds like a pretty redneck way of doing it, but it helps to understand the theory.

[Mikeee]

Fluke 87 meter..fairly cheap at walmart

In my wildest dreams I thought I would NEVER see the word Fluke and Walmart in the same sentence.

[Mikeee]

Here's how I'm envisioning this process: pull the connector from the sending unit. The connector has two leads connected to wires. Connect a wire from one lead to one side of a variable resistor such as a rheostat. Connect the other side of the rheostat to the second lead in the connector. Connect an ohm meter - one lead to each side of the rheostat. Turn the ignition key to the "on" position. Adjust the rheostat until the ohm meter reads 1305 ohms. Check the temp gauge - it should read 100 degrees. Adjust the rheostat until the ohm meter shows 49.5 ohms. The temp gauge should read 260 degrees. Does this sound right?

 

I already have a decent multi-meter, but coming up with the right rheostat may take some research. A friend suggested using a really long steel spring that has been slightly sprung (so the coils don't touch). Attach a wire to one end, and the other can be moved anywhere along the spring. The greater the distance from the first wire, the greater the resistance. With an ohm meter attached to each lead in the connector, just move one wire either direction until the desired resistance is shown on the ohm meter. That sounds like a pretty redneck way of doing it, but it helps to understand the theory.

Some sending units have one side to ground. Best to check the wiring skids.

 

On the "long steel spring".

Good luck on that.

Maybe if you were Macgyver.

There has to be some kind of electronics repair shop near ya.

The variable resistor is smaller than a stik pen cap.

[bronyaur]

"Some sending units have one side to ground. Best to check the wiring skids."

 

Good advice. I'll make sure I check.

 

"On the "long steel spring".

Good luck on that.

Maybe if you were Macgyver."

 

Yeah, not saying I would try it, but like I said it helps to envision the theory.

 

There's a Bombs 'R' Us nearby. I'd like to go in knowing what I want.