Are my coolant and voltage gauges accurate - where to test

[AuroraGirl]

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Ive noticed the voltage gauge sticks at 8 or so now a days rather than 12 (or 14 when revving), would sticking my voltmeter on the battery while running and confirming the number is the same tell me gauge accuracy? Or would the voltmeter read higher? I guess I want to know if my alternator/wiring is going bad.

Also, the coolant gauge never goes over 1/4 or so where it is shown when warmed up. thats all warmed up. that seem normal?

 

[AuroraGirl]

and yes im aware of the very broken needle, lol.

 

[Goldie Driver]

These gauges seem to be fairly accurate in my view, so the voltmeter to me is telling you more than likely a bad alternator. I paid like 36 bux at Advance Auto for a lifetime one, but you may have an OE spare in your pile.

The temp gauge seems about right, too. Mine runs at the quarter mark or a needle width or two above after the 195 thermostat opens. Opening is like 3/8 on the gauge and then it falls.

Goldie cools down at idle, too, versus the highway.

The 77 I had seemed like it was always below the quarter mark for temp. I assumed it was a 180 stat, but I was told here that factory was 195 and I don't recall it being changed, so who knows.

The heater worked and the motor never overheated, so no sense in messing with success.

 

[AuroraGirl]

Im confident coolant gauge makes sense then. seems strange to not utilize 2/3 or so of sweep.

 

[Goldie Driver]

Im confident coolant gauge makes sense then. seems strange to not utilize 2/3 or so of sweep.

Yeah, I agree.

On mine the middle mark would probably match the later ones that said 210, and I would probably be pulling over to figure out what the hell.

So, its a happy gauge staying on the left side and the rest is just to make it look like the rest of them.

My 99 Camaro has basically a dummy temp gauge as people apparently complained because the gauge moved around.

No ****, sherlock? A temp gauge needle should move, not just tell you normal until too late, overheat.

 

[C10MixMaster]

voltmeter and battery voltage should be close. temp gauges came in 3 different ohms ranges if the sender and gauge dont match it wont read correct.

For Truck Years: 1967 - 1973
The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 76 Ω
Right Line (Hot) when sender resistance = 51 Ω
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

 

[1987 GMC Jimmy]

If your engine bay ground network isn’t right, it can also impact those readouts.

 

[Turbo4whl]

Yes, put your multi-meter on the battery when running the engine. Should read right around 14 volts. (13.9-14.2 V) Engine will not start at 8 volts. Most likely the gauge is bad or has a bad connection somewhere.

 

[75gmck25]

If you take the bezel and clear plastic off the cluster you can then remove the voltage gauge. Multimeter leads will fit into the spring clips behind it and you can check the actual voltage. My bet is a bad gauge.

GM changed electric temp sending units over the years, and finding the right match is challenging. I need the single button wire connection, and the first couple of units I found would barely get the gauge to about 1/4 scale. I also have a mechanical gauge, so I knew it was getting up to 190. I finally found a good match, and now it reads a little more than halfway between 1/4 and 1/2 at 190, and just about touches 1/2 at 200. I think this is a good range. I would have to look at the box to remember which one I finally used.

Also remember that the SBC switched back and forth from 1/2” to 3/8” threads for temp sending units. My GM crate engine has 1/2”, but some original engines from the early 70’s had 3/8” threads. My new aftermarket heads use 3/8”, so I had to move the sending unit to the intake manifold.

Bruce

 

[Grit dog]

If the truck overheats, temp gauge is wrong.
If the battery goes dead, volt gauge is correct.
Properly Working gauges in a 40 year old unkept beater with a heater are generally a bonus and mostly a stroke of luck.

 

[Bextreme04]

My 1980 temp gauge with all original gauge, OEM temp thermostat, and I think original sending unit reads dead center on the temp gauge when warm. Volt gauge seems to be accurate too. Like others have said, put a multimeter on the volt gauge connections and see what you get. If it is reading 13v or higher, your gauge is bad. If it reads lower than that, check at the battery. If you see 13v or higher at the battery and 8v at the gauge connections, you have a good gauge, battery, and charging system and just have a poor connection somewhere between the battery and cluster.

 

[PrairieDrifter]

My volt gauge reads high compared to the actual alternator output, reads almost at the red line at any rpm, I think it reads around 9 at key on. Voltmeter says it works perfect, 14.6 volts

my temp gauge usually hangs out between the 1/4 line and a little bit over the 1/2 line.