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Old 03-18-2022, 07:55 AM   #1
BigMF1155
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Default Volvo 245 temperature gauge not working suddenly?

1984 Volvo 240 with D24 temp gauge went to max value this morning and I shut the car down and waited for it to drop and now it sometimes rises to the middle and drops way down.

It also went to max a couple of times but the engine didn't overheat
I would like to fix this issue quickly because I have no idea if it overheats now
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Old 03-18-2022, 08:34 AM   #2
TestPoint
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The first question:

Is the engine over heating? Got a IR thermometer? Any other sign that it really over heating?

Really sounds like a wiring issue. The '84 is dead center of the wiring harness insulation problem time frame. Take the lead off the thermostat sensor and see if the problem continues.
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Old 03-18-2022, 08:55 AM   #3
BigMF1155
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Quote:
Originally Posted by TestPoint View Post
The first question:

Is the engine over heating? Got a IR thermometer? Any other sign that it really over heating?

Really sounds like a wiring issue. The '84 is dead center of the wiring harness insulation problem time frame. Take the lead off the thermostat sensor and see if the problem continues.
I took it off and after a minute the gauge suddenly went to the red line. Engine temp is 50c water hose after 25 minutes and engine block 71c.

What should I check?
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Old 03-18-2022, 08:57 AM   #4
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Quote:
Originally Posted by TestPoint View Post
The first question:

Is the engine over heating? Got a IR thermometer? Any other sign that it really over heating?

Really sounds like a wiring issue. The '84 is dead center of the wiring harness insulation problem time frame. Take the lead off the thermostat sensor and see if the problem continues.
I plugged the wire back in and immediatly after starting the engine, the gauge started going down
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Old 03-18-2022, 09:14 AM   #5
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Replace the wiring harness.

The gauge provides power which goes to a resistance ground in the sensor. Without the sensor connected the wiring harness is providing that ground.

You can temp wire around it with a wire from the sensor to the grey connector on the firewall. I wouldn't mess with the harness itself as you will only surface other problems.

Had the same problem with an '82 D24. That engine uses so few wires that I rewired it myself rather than purchase a harness.

Last edited by TestPoint; 03-18-2022 at 09:23 AM..
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Old 03-18-2022, 09:19 AM   #6
apachechef
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Quote:
Originally Posted by TestPoint View Post
Replace the wiring harness.
couldve slam dunked the answer with this link, lol:

https://www.prancingmoose.com/volvoh...html#240series
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Old 03-18-2022, 09:41 AM   #7
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I messured between the sensor wire and the round instrument cluster connector and didn't read any connectivity. Does this confirm that it's the harness?
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Old 03-18-2022, 09:52 AM   #8
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Looking toward the gauge you should be seeing about 5v as there is a voltage regulator on the other side of the gauge. Ignition must be on to see voltage.

Based on your symptom of the gauge going to the top you should be looking for a ground originating in the wiring harness. Look for the ground with the ignition off.

As a come-and-go problem you might suspect that the ground would come-and-go.
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Old 03-18-2022, 10:12 AM   #9
apachechef
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Quote:
Originally Posted by TestPoint View Post
Replace the wiring harness.
couldve slam dunked the answer with this link, lol:

https://www.prancingmoose.com/volvoh...html#240series
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Old 03-18-2022, 09:32 PM   #10
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Some times the pins thru the instrument circuit board need tightened.
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Old 03-18-2022, 09:39 PM   #11
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Gauge to top screams ground within wiring harness.
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