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Old 08-08-2018, 08:19 AM   #1
70inbville
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Join Date: Oct 2011
Location: bartlesville ok
Posts: 93
gauge question

are gauges year specific? I have an 83 gmc oil pressure and temp needles were broken off, replaced with gauges from unknown years and now they are pegged. changed senders for both with no change in status? any ideas?

Thanks in advance.

chip
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Old 08-08-2018, 09:22 AM   #2
blindbug
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Join Date: Oct 2017
Location: Louisville, KY
Posts: 163
Re: gauge question

In 76 the C10 went from an 'AMP' meter to a 'VOLT' meter. 76-77 c10s have a mechanical oil gauge on it.

I know they were broken off, but were the needles pegged before?

Pegged is usually an indication that there is a grounding issue occurring somewhere. It is often the case that it is the sending unit is bad and grounding out... but just as likely to be a frayed wire or a printed circuit issue. Have you checked that your engine block is properly grounded? It could be the engine ground since both are getting pegged.

Also, double check that you didn't get the On/Off (idiot gauge) style sending units. Could also check the output of the sending units via a multimeter. For the Temperature sending unit:

For Truck Years: 1974 - 1978

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

For Truck Years: 1979 - 1990

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

Check the sender's resistance under actual operating conditions. Remove the sensing lead from the sender and - with the engine cold - get an initial resistance reading. One probe on the sender's terminal and the other to a clean nearby spot on the cylinder head. As the coolant warms up, keep checking to confirm that the resistance across the sender begins to fall.

Can also check the resistance across the back of the gauge itself. Since the sending units are new, if the gauges weren't pegged before, it could be that you have bad gauges. There is a resistor on the back of some of these gauges that can go bad and cause it to not work.
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Old 08-08-2018, 11:22 AM   #3
70inbville
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Location: bartlesville ok
Posts: 93
Re: gauge question

thanks for the info
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