Temp Gauge & Sender Issue

[Howard P.]

I am having a problem with the temp gauge registering very low on the gauge on my 67 Big Block. I've checked the wiring and all seems OK and the ground is also secure, though the gauge barely moves from full cold position when fully warmed up. My Ratech lazer gauge reads 180 degress at the top rad hose and 171 degrees at the intake inlet so I know we are reaching good temp.

I don't know whether I may have simply a faulty sender or perhaps the gauge is bad. The sender is a GM AC Delco replacement unit.

Any thoughts would be appreciated

[Timothy B.]

Re: Temp Gauge & Sender Issue

Howard,
Check to see if the sender has been installed with too much sealant thus keeping the circuit from grounding. I have the same problem with my 63 only it's the other way (too hot)

[Jack H.]

Re: Temp Gauge & Sender Issue

This one's RARE, but it can happen... If you study the wiring diagram for your car, you'll see the power line for the temp sender (20G Pink) runs back to a node in the dash harness that splits six ways. Other taps off the node power other circuits like the fuel gauge, parking brake alarm, backup lamps, Etc.

If there a faulty load on one of these parallel circuits (shorted but not so fully shorted that the fuse blows), you can be dropping voltage to the point there's insufficient branch circuit current to properly power the temp sender resulting in a permanent low reading.

The way to trouble shoot, is to study the wiring diagram and disconnect all of the other branch loads from the power node. If your temp gauge immediatly starts to work properly, reconnect the other paths, one at a time, until the gauge stops working then go correct the problem....

One culprit know to cause this kind of 'funny' is a defective or improperly designed fuel tank sending unit. Some of the 'Made in China' sending units are known for this. BUT, you'd also see the gas gauge fails to properly register liquid level in the tank....

[Howard P.]

Re: Temp Gauge & Sender Issue

Thanks for the tips I will try them and get this sorted out