Question about temp gauge reading high

[fordsucks!]

My temperature gauge reads 3/4 when the motor is running at very normal temp, 190* at the thermostat neck.

I've already bought a new Sender but have not installed yet, but I just tested the gauge by grounding it and here is what the gauge does:

Gauge with motor fully cold, key in ON position



With temp wire grounded, key ON, is the needle supposed to go this far?



What do you think, bad gauge or bad sender? I feel like the gauge should be sitting below the cold mark when it's fully cold...

 

[dyeager535]

The gauge should go well beyond "C" just like it does "H", with the wire NOT connected/grounded. Verify that.

It's almost never the gauge, the printed circuit having bad contacts is far more likely.

 

[fordsucks!]

Thanks for the response. In the first picture above, that was with engine cold and the wire connected to Sender.


This is with the wire completely disconnected from everything. Does not sit well below the C like you described, what do you think?

 

[dyeager535]

The gauges seem pretty standard, I dont think GM ever used a pin to limit needle movement, so I'd say that isnt right. It makes sense that the gauge reads high if it "rests" or starts in a higher than normal position.

I may be able to test mine tonight or tomorrow, but I'm quite certain the gauge should respond the exact opposite with the sending wire grounded, then open.

The oil pressure gauge works the same way, disconnect it if you can, and see what it does.

 

[fordsucks!]

Thanks bud. I ordered a $20 used OEM gauge, will get it next week. If that doesn't work then i'll try the new sender.

 

[dyeager535]

Thanks bud. I ordered a $20 used OEM gauge, will get it next week. If that doesn't work then i'll try the new sender.

If you are getting that far into it, you'll have access to the printed circuit. If the new gauge works, I'd not toss the original. The ceramic resistors on the back do go bad (and they also are different resistive values), and corrosion on the terminals and/or nuts holding the ceramic resistor in place can also affect the readings.

 

[fordsucks!]

If you are getting that far into it, you'll have access to the printed circuit. If the new gauge works, I'd not toss the original. The ceramic resistors on the back do go bad (and they also are different resistive values), and corrosion on the terminals and/or nuts holding the ceramic resistor in place can also affect the readings.

I'll take a look when the new gauge comes in. I already had this temp gauge out to see if there was any adjustment on it but no avail. Didn't think about corrosion but I didn't see anything excessive either.

 

[dyeager535]

I just tested mine, it does not go past what is the "C" mark on yours with the sender disconnected. Learn something new every day.

 

[fordsucks!]

Ah crap. Guess I'll just replace everything one by one, the gauge and sender were cheap so no big deal.

 

[nvrenuf]

Any chance the wire going to the sender is grounded somewhere? I've seen a gauge point to 3 o'clock like that with the wire laying on a header tube.

 

[fordsucks!]

So I replaced the gauge, same exact needle reading.

I then replaced the sender, drained and refilled the system with 75% distilled water & 25% green coolant, same exact needle reading.


I did not yet replace the thermostat but I don't think motor is overheating. If the motor was really at 240 like the gauge indicates, wouldn't I see some symptoms of boiling, or radiator pushing fluid into the Overflow? With IR temp gun, the highest temp i've registered was 195 at the the tstat neck on a hot day. I have not crossed checked with a second temp gun but the motor feels cool, I can put my hand on the radiator cap and upper rad hose and they are never burning hot.

Ready to give up... thanks for your input so far. You really think a failing printed circuit behind the gauge cluster could be at fault?

 

[fordsucks!]

Any chance the wire going to the sender is grounded somewhere? I've seen a gauge point to 3 o'clock like that with the wire laying on a header tube.

In that photo, I grounded the wire on purpose just to see where "full hot" is.

My problem is that the gauge always reads between 3/4 and full hot (ill add a picture) even though everything seems to be okay with the cooling system as far as I can tell.


Now that I've replaced the gauge and sender, I'm starting to wonder if my motor is actually overheating and I am not checking properly

 

[bp71k5]

What’s the actual temperature reading with an IR gun or thermometer on the water neck? Without an actual number, the gauge doesn’t mean much except to tell you when it runs hotter or colder than other times.

 

[fordsucks!]

What’s the actual temperature reading with an IR gun or thermometer on the water neck? Without an actual number, the gauge doesn’t mean much except to tell you when it runs hotter or colder than other times.

The highest I've been able to get it to was 195 at the thermostat neck, driving hard on a hot day. Am i right to assume thermostat is okay? Reading about airlock behind thermostats and wondering if maybe I have something like that going on

 

[bp71k5]

Thermostat just controls the minimum temperature the engine operates at. If the water in the system stays below 200, there’s no problem. Measuring the neck when the thermostat is open seems best place to measure. Sounds like your wiring may be compromised somewhere if the gauge and sender is ok. You might wire it up independently just to be sure.