C2 Temp Gauge - Ground issue?

[Rob M.]

All---

You all have helped me solve many small issues in the past, so I'm hoping that this will be an easy fix also. My temp gauge is acting like there's a ground problem. On a cold start after inserting the key and turning to the ON position, the temp gauge needle will go hard RIGHT and peg bottom. The exact opposite of what it should do. After the car warms up, the needle will jump back to the regular (normal) position at @180-190 deg. Wiring harnesses are new, sending unit is a replacement, and it's a small block. Any thoughts of where to start?

Thanks in advance.

[Mike M.]

Re: C2 Temp Gauge - Ground issue?

if there are two terminals on the back of the temp gauge, and i recall there are two, try reversing the two wires foing to the terminals. mike

[Jack H.]

Re: C2 Temp Gauge - Ground issue?

Pointer needle resides between two opposing electro-magnets in the gauge. One set is fixed in magnetic strength, while the opposite side varies based on how much current flows through the wiring path to the temp sender.

When engine is cold, the variable resistance of the temp sender is high and current along that path is low. This means the magnetic strength of the of inductor pulling the gauge needle toward the HOT side is weak and dominated by the opposite inductor who's current and resulting magnetic strength is fixed that pulls the needle toward the COLD side.

For the 'bias' side of the gauge to function properly (fixed inductors pulling the needle toward the COLD side of the dial), the gauge HAS to be properly grounded in the instrument cluster (that's what completes the bias side of the gauge's circuit). If temp gauge is 'loose' and making intermittent ground contact with the instrument cluster, you wind up losing the 'bias' drive and even though there's little current flow to/through the temp sender, without the opposing magnetic flux to pull the pointer needle to the cold side of the dial, the needle will PEG to the hot side.

Note, that as the car runs a while and the engine heats up, the instrument cluster is also experiencing vibration which could 'cure' the temp gauge's loss of ground reference in the instrument cluster. Bottom line: there's two ways to generate the symptoms you describe:

(1) The wiring path from the gauge to the temp sender is momentarily short circuited to ground (faulty connection at the back of the temp gauge, insulation on the lead wire to the temp sender is skinned, there's a 'foreign' substance on the temp sender causing the center pin terminal to short) and the fault 'cures' itself with engine heat/vibration.

(2) The temp gauge has a marginal ground reference in the instrument cluster and this fault 'cures' itself with engine heat/vibration.

[Rob M.]

Re: C2 Temp Gauge - Ground issue?

Great post. I'll run those down and see what comes of it. You guys are awesome! Thanks for the help.

Rob

[Ray C.]

Re: C2 Temp Gauge - Ground issue? *NM*

[Ray C.]

Re: C2 Temp Gauge - Ground issue?

I had the same problem on the 65 and I cleaned the terminals on the temperature gauge and made sure that the nuts were tight. The problem went away.

Ray