Temp gauge issues

[78K20fallguy]

Hi guys I have a 1978 Chevy k20 with a 400sbc I’m having issues with my temp gauge I feel that it’s not reading right. I have the msd atomic efi and I was looking at the temp reading on it and it says 190 but I look at the gauge on my dash it reads below the first mark off of cold. So I’ve been ohming my temp sender and at 190 degrees it reads 135 ohms. So I wonder if it’s a wiring issue?

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[mlsceo]

Sounds like the resistor on the back of your gauge is faulty. On my 77 c10 the gauge would read low till I replaced it with a new one from LMC. Around $40 if I recall correctly.

 

[78K20fallguy]

Ah ok. Is it possible to solder a new one in? I did ground the gauge out and it sweeps all the way to the hot side too.

 

[Snoots]

For Truck Years: 1967 - 1973

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ohms
Middle Line when sender resistance = 76 Ohms
Right Line (Hot) when sender resistance = 51 Ohms

For Truck Years: 1974 - 1978

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ohms
Middle Line when sender resistance = 68 Ohms
Right Line (Hot) when sender resistance = 46 Ohms

For Truck Years: 1979 - 1990

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ohms
Middle Line when sender resistance = 96 Ohms
Right Line (Hot) when sender resistance = 55 Ohms

 

[Snoots]

Ah ok. Is it possible to solder a new one in? I did ground the gauge out and it sweeps all the way to the hot side too.

You could but you need a high wattage resistor. Something on the order of 10 watts. They are held to the gauge by nuts. It's best to replace the resistor with the right type (what @mlsceo said).

 

[78K20fallguy]

Ah ok thank you for the input.

 

[Trucksareforwork]

You could but you need a high wattage resistor. Something on the order of 10 watts. They are held to the gauge by nuts. It's best to replace the resistor with the right type (what @mlsceo said).

The resistor in mine went bad and I just put a new resistor in behind the existing one and cinched the tab nuts down on it. I think the resistor cost me a few bucks for a hundred of them. Still got 99 in the toolbox.