Dash Temp Reads 160 Engine at 210

[Chris86]

1992 GMC k2500 5.7, as the title states Dash temp when the engine is hot reads 160, reading temp beside sending unit with a laser thermometer gives 210. This is with a new Standard brand Sensor. When I start the truck the temp gauge on the dash pings completely to the right then returns to the left like normal. Thermostat works fine. Anyone have a troubleshooting guide to check the wiring? I also found a discussion about this same problem on another forum about using a sending unit with a lower resistance, but the hyperlink to the details led to a page that was long gone. Anyone know anything about this?

[silveradosid]

those sending units usually run between 30 to 300 ohms. your gauge is just like an ohm meter. at 300 ohms the engine is cold and as the number lowers the gauge goes up in temperature. if the gauge doesnt read right look for a corroded connection that is causing the resistance to stay higher than it should be

[Chris86]

Thanks for the reply, much appreciated!

[thx1138v2]

I never did find an accurate temperature sender after trying 5 different ones by different manufacturers which all said they were 100% compatible with my '94 GMC C1500 4.3L. I think they just look at the physical attachment, i.e. size, threads, connector, etc instead of electrical compatibility. At the time I did quite a bit of research on the issue and found that the sensors use a logarithmic response rather than a linear response.

 

What I finally ended up doing was removing the pointer on the gauge with the coolant temp at 210F by the IR thermometer and reposition it so it pointed to that reading on the gauge. With the coolant at ambient it reads high, like 140 or so, but it reads good at operating temperature. I figure that's better because I'm worried about overheating, not low temps (like freezing) which the gauge isn't going to show anyway.