Oil and Temp gauges

[mjb765]

70 Cuda rallye dash. Had the gauges restored by Instrument Specialties about 6 years ago. Ammeter converted to voltmeter. Temp and oil pressure gauges read very low. Fuel gauge reads fine. Oil pressure is 45-50 psi while driving (on an external Auto Meter mechanical gauge), but dash gauge is barely 1/4 of the way up. Temp running at 190 according to Sniper display, but temp gauge is also 1/4 of the way up. Does the voltage limiter on the gauge cluster control both these gauges and not the fuel gauge??

 

[pschlosser]

In order to provide accurate indications at all times, the fuel, temperature and oil pressure gauges need a regulated voltage source that is constant regardless of the car's battery charge state. There is a voltage regulator thing-deal that feeds all three. If it's output is wonky, and 2 of 3 gauges appear affected, that would be my guess. It's possible the fuel gauge still works fine with limited regulator function. This device is found on the back of the rallye instrument cluster.

 

[Challenger RTA]

The grounds. Someone might have put to much sealer on the threads of the sensors.
Bulkhead connector, bad connection.

 

[mjb765]

I was thinking volage regulator for the gauges as well......I will test the sensors by grounding the wire and see if the gauges go full sweep.

Thanks for the suggestions.

 

[Challenger RTA]

volage regulator for the gauges

When it goes bad. From what I have seen it wipes the gauges out too.

 

[mjb765]

When it goes bad. From what I have seen it wipes the gauges out too.

Well...now that would suck......at that point Dakota Digital here I come...but I was hoping not to spend $2k this winter on this.

 

[Challenger RTA]

The volage regulator for the gauges regulates the voltage to 5v. 12v just fries them.

 

[mjb765]

The volage regulator for the gauges regulates the voltage to 5v. 12v just fries them.

I know....if it was going to die i would hope it wouldn't allow full voltage out to the gauges. No voltage would be better.

 

[Deathproofcuda]

I know....if it was going to die i would hope it wouldn't allow full voltage out to the gauges. No voltage would be better.

It can definitely happen. When my went, it died closed, so did send 12 volts to the gauges and fried all of them.

 

[mjb765]

It can definitely happen. When my went, it died closed, so did send 12 volts to the gauges and fried all of them.

Weird that it didn't fry the fuel gauge and the other 2 are working, just not accurate.

 

[Deathproofcuda]

I was thinking volage regulator for the gauges as well......I will test the sensors by grounding the wire and see if the gauges go full sweep.

Thanks for the suggestions.

This test is fine, but you should also do as Challenger RTA suggested and verify that the ground connection between the sending units and engine block are good. An existing, but weak, ground connection would could cause your problem. Use a jumper wire to connect from battery ground to the sending unit body and then check to see if the gauges respond.

 

[mjb765]

This test is fine, but you should also do as Challenger RTA suggested and verify that the ground connection between the sending units and engine block are good. An existing, but weak, ground connection would could cause your problem. Use a jumper wire to connect from battery ground to the sending unit body and then check to see if the gauges respond.

I will do that before removing the cluster or replacing sending units. It's a quick, easy test.

 

[Deathproofcuda]

Weird that it didn't fry the fuel gauge and the other 2 are working, just not accurate.

Have they always been inaccurate, or is this something that changed more recently?

I'm betting on bad ground connections between the temp and oil pressure sending units and the block. Maybe someone used teflon tape or too much sealant on the threads?

If they have always been inaccurate, you can take the gauges out and re-calibrate the needle position.