Temperature Gauge Issue

[sonicbluezx3]

Okay I have a question for you guys....

First of all, let me explain a little bit. My truck (1986 K10 Shortbed) originally came with a 4.3L V6 engine. The guy I bought the truck from swapped in a 6.2L diesel engine. He used the original wiring (set up for the gas engine) and everything worked fine. I just did a total overhaul of the body, and in doing so, I put a diesel cluster in. Now, the temp gauge pegs out as soon as I turn the key on ignition. Now I know my truck isn't running hot like that because I didn't even have it running when the gauge was pegged. To make things more complex, I replaced the temp gauge that was in there with another one because I accidentally broke off the needle. The thing that makes me think it isn't the gauge is that the gauge that I broke the needle off of pegged out as well. The only one that worked was the one from the cluster for gas. I know the temperatures are different on the two, but it's only by 20 degrees.

My question is.... is the wiring different? Is it likely that I have a faulty gauge? Or sensor? I just don't want to start throwing parts at it until I can figure out which part it is, and I don't know much about these gauges.

Thanks for the help!

[Captkaos]

The sensor in the block must match the gauge in the cluster.  Since you said you had a setup that worked, just replicate it.  The Diesel and Gas Gauges are not the same.

[DnStClr]

Since both gauges pegged, you know the wiring is ok. There's a signal getting to the gauge. So concentrate on the sensor.

[sonicbluezx3]

So he could have kept the sensor from the gas engine and used it in the diesel?

[Captkaos]

yes.

[sonicbluezx3]

I asked him and he said the sensor is what was in the 6.2... Im wondering if i should just replace it and see if that fixes it since they are cheap.

[sonicbluezx3]

I should also mention that when i shut off the truck/key, the gauge stays pegged out.

[Captkaos]

If that is what he used I would try that, either way they need to match.

[sonicbluezx3]

Right.... I'm saying he used the temp sensor that came with the engine (so the temp sensor is for a diesel) and he used the temp gauge that was in the gasser cluster. So I'm not sure if it would be the temp sensor.

[timthescarrd]

Generally a gauge will peg like that if there is a ground problem (I.E. a wire grounding to the body where it shouldn't be)

[DnStClr]

Yes. The grounded wire would complete the circuit, and with no resistance the gauge would peg.
The gauge is actually a voltmeter. It reads temperature because that's the system it represents. When the engine is cold, the temp sensor has high resistance. but as the engine warms up, the sensor responds and loses its resistance, allowing more voltage to go to the gauge. When a gauge is pegged, it means the sensor has lost all of its resistance OR there is a grounded wire, either of which will peg the gauge.
My guess is that the gauge stays pegged because it has overridden its operating range because of the low resistance and high voltage. there's a little spring in the gauge and the voltage causes it to expand because it's bimetallic-there's two different metals- so they react to the voltage and drive the needle higher.

[sonicbluezx3]

So does that mean i should replace the gauge?

[numbr3t]

Sounds like you should check the length of the wiring to make sure it's not cracked and grounding somewhere on the body.

[sonicbluezx3]

I'm not sure if this makes a difference, but I have the battery disconnected and it still pegs. I will check the wiring tomorrow night when I get home from work and see.

[JB76]

There is no difference in sending units between gas/diesel v6 or v8, the only difference is one unit for gauges and one for idiot light dash.