74 C10 Temp Gauge

[Rapid Roy]

Gauge stopped working intermittently. Lately, sometimes when key to ON, hand would move from below C to first mark on gauge then would drop to below C when started. Next, it would go from below C to first mark when key to ON, would drop below C in about 2 seconds without starting engine. Then did not work. Have replaced gauge with new one and same situation. Does anyone have any ideas? Most of the time now hand does not move at all.

Replaced temp sending unit and connector (nail head) last fall. This problem started within the last month. Before that worked fine.

TIA

[zieg85]

That plastic printed circuit board on the back of the instrument cluster is usually the culprit.

[bd]

Use a soft pencil eraser to gently burnish the connections between the copper foil and the gauge spring clips and between the copper foil and the terminals of the harness connector.  Be careful that you don't peel the copper foil loose from the printed circuit board (PCB).  Increase the tension between the spring clips and the gauge pins very slightly while you have the clips out of the cluster housing.  Smear a sparing amount of clear dielectric grease or antioxidant paste between the gauge spring clips and the PCB.  Finally, clean the cluster ground wire connections to the cab sheetmetal at the left kick panel.

[Rapid Roy]

Update.....After exhausting all gauge testing I could, decided to replace sender. Fixed issue even though I had replaced it last fall. Now gauge hand consistently stays at 12:00 without AC and 1:00 position using AC.

Shocked it was just sender.

[blazer74]

My 74 has original gauge and  sending unit that has been relocated to the intake due to a vortec head swap.
Reads at the first mark with a 192 thermostat and at operating temp.

Don't recall ever reading 12 o clock even before the vortec swap.
What really matters is what is normal for your vehicle.

[Rapid Roy]

I believe it is a difference with different gauges. Swapped to my original gauge 2 days ago, it reads at the first mark without using AC. Reads from first mark to 12:00 position with using AC. I know it is not overheating, just the gauges sensitivity I believe is the main factor.
Thanks for the info.

[Militiaman55]

Just for info, my 74 K10 temp gauge reads exactly where blazer74's does (w/ 195 degree thermostat).