Temp Gauge question; Calibration?

[Tbruz]

1997 Tahoe, 5.7 engine.
My OCD is acting up and I'm tired of seeing my temp gauge read about three hashmarks too low for the actual temp(verified actual temp at 187 with scanner).

Each has hash is about 14 degrees so the indicated temp is showing between 140-150.

Today I replaced the coolant gauge temp sender in the DS cylinder head with a AC Delco part with no change; I then used a Standard Motor part, again with no change; Both read exactly the same as the original suspect part, 140-150.
Grounding out the single signal wire to the gauge itself causes the gauge to peg above the 260 mark so the gauge itself is working at the extreme end.

any ideas or suggestion besides "live with it" or "get over it"

Is there a test/calibration procedure like "X "resistance should indicate "Y" position on the gauge itself?
I realize its an insignificant issue and not really a problem; its just stuck inside my head now.

Thanks in advance
Tbruz

 

[Doubeleive]

someone would have to take the gauge apart and move the needle, otherwise if you got real technical with it you could maybe put a very slight resistor on the harness to make it read where you like, not even sure what resistance would be required you would need to know what the service manual says the oem resistance should be and go from there

 

[Fless]

...otherwise if you got real technical with it you could maybe put a very slight resistor on the harness to make it read where you like, not even sure what resistance would be required you would need to know what the service manual says the oem resistance should be and go from there

If the specs (ohm value vs. temp) aren't in any documentation, measure the resistance between the engine block and the signal terminal on the sender with the wire disconnected. Document that and pencil up a chart using two or three resistors as a test. Might be a hit or miss proposition to determine the resistor you need, but it can be done with persistence and perhaps some math. Remember that two resistors connected in parallel with be a lower ohm value than either by itself.

Long shot, you might also verify the resistance between the engine block and the battery negative, see if there is much there. Shouldn't be much, and that could affect the sender.

 

[Fless]

Is there a test/calibration procedure like "X "resistance should indicate "Y" position on the gauge itself?

One other thought: someone who repairs these instrument panel clusters may know that, if they calibrate when they repair them.

 

[east302]

GM’s diagnostic implies that it is not meant to be very accurate as the test merely checks to see if the needle pegs at the extremes. The strange tick mark values seem to back that up as you cannot easily read a value without doing some math in your head.



I have three 98 models, all read around halfway between 100 and 210. My opinion- it’s as good as it gets without putting in a gauge that outputs the ECT sensor value.





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[drakon543]

going by the documentation that east has provided the wiring for the temp sensor to the gauge could have a bad spot. a bad spot in the wire can cause resistance in the wire causing the gauge cluster to read incorrectly. 30 degrees off can be a small resistance. as the ecm is seeing a proper reading and the cluster is not the temp sensor goes to the ecm and the cluster or to the ecm then the cluster. if you have a meter with long enough leads and someone can provide a wiring diagram for that circuit. first test from the sensor plug to the ecm for ohms across just the wire. then from the sensor plug to the input wire on the cluster. if its sensor ecm then cluster, test sensor to ecm then find the wire from the ecm to the cluster and test that for ohm. lastly test the ground wire for the cluster. perform those tests with the temp sensor unhooked if your ohm readings are higher than?? 3ohms across the wires id think the problem is the wires. if those tests show under 3ohm id say cluster. without having a wiring diagram just going by east302's information that test should point you directly to the cluster or a problem elsewhere.

 

[Tbruz]

Thanks for everyone's input.
Based on the same reading with three senders, I'm ruling out the sending unit being bad on the head - too bad as that was such an easy fix.
I was able to dig up a spare cluster that a friend had and I will install that to get a reading using a different gauge. If I get the same reading with a different cluster then its safe to assume its the wiring.
He's giving me that cluster so Ill use as I see fit as he no longer has a OBS vehicle.
Ill also try reading the resistance I'm getting at the actual gauge once i get the spare cluster installed.
Will report back with any updates.
tbruz

UPDATE: Its the gauge itself!
I replaced the cluster with the "spare" cluster provided me and the gauge is now reading almost three lines higher than my original gauge.
I am in the process of swapping the spare cluster TEMP gauge over to my original cluster.
Re-bulbing and installing my NOS pointers as well.