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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by Dr. Phil on Thu Jul 27 14:34 CST 2017
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I have a 1988 Volvo 240DL and about 2 weeks ago, I started the car in the morning and in about 30 seconds, the temperature gauge rose to hot. I turned the motor off. A few days later, I tried it again and the same thing occurred. The next day, I just turned the ignition switch to on and the temperature gauge went to hot. My next step was to replace the temperature sending unit (2 wire) which feeds the computer. It was located under the 3rd cylinder and behind the air manifold. It took some time to conjure a method for removal and installation. Before installation, I checked the resistance of both old and new sensors with room temperature and hot water. The new sender seemed to respond a little better, ergo I installed the new one. With the ignition switch on, I checked the voltage at the 2 wire connector and is was about 5 volts. Now, I turned the ignition switch to on and the temperature gauge goes to hot again. Now, I replace the temperature switch unit (1 wire) which is under the 2nd cylinder and behind and under the air manifold. This temperature switch unit feeds the temperature gauge. This unit was easier to remove since I had not replaced the large vacuum hose yet. There were no tests or checks to perform. Again, I turn the ignition switch to on and the temperature gauge goes to hot. Now, I think that I have only to check the operation of the engine thermostat which I replaced about 3 years ago with a $21.00 failsafe thermostat. I drained the antifreeze, removed the thermostat and checked its operation. It opens at the stamped 180 degree F. Now, I have to reinstall the thermostat, refill the antifreeze and run the motor to remove any air pockets in the motor. And, of course, refill with more antifreeze as needed to maintain the correct level. Does anybody have any other suggestions?

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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by 1pocket on Sat Jul 29 03:56 CST 2017
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a basic test to ascertain if the gauge itself is good or bad has always been to turn the key on and ground the yellow wire to the block. if the gauge is good it goes to red hot straightaway.

sounds to me like the yellow wire is grouding to the frame or engine somewhere along its route.

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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by rstarkie on Fri Jul 28 19:45 CST 2017
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last visit: Fri Oct 24 10:14 CST 2014

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Is the temperature compensation board still in place on this car? I have never heard of it causing the gauge to go to hot by simply turning on the key, but it may be worth exploring.

If your car still has the troublesome board here is the procedure for removing it and having an accurate gauge: http://cleanflametrap.com/tempFaker.html

Randy

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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by machine man on Thu Jul 27 19:54 CST 2017
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last visit: Wed Oct 22 15:40 CST 2014

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Hi,

You might take a look at the gray connector on the fire wall.
The engine side harness connects there and it has a wire in it that runs to the Coolant temperature sensor.
Starting in 1984 these wiring harness have what is considered "biodegradable insulation" on their wires. It may not have ended until the 1989 year. I have a 1984 sedan and a 1986 wagon that each one of those harness. The 1984 was repaired before I bought it.

On the '86 I think there was two of them in there that caused a weird issue with the car running because as I remember I think it affected the ECU Coolant sensor reading.

The worst wire I found was the yellow one that went to the engine Coolant sensor for the gauge. I only replace one wire because the other one would not budge. My thought was it split in two directions.

I opened up the harness for about eight inches to get pass a joint to solder on a new wire. I then pulled out the bad wire and it pulled in the new one.
This stopped a rough running issue. I can only think that two badly insulated wires were touching each other.

In your case, that yellow wire might be touching a wire that either goes through a resistance to ground or is being over powered by another circuit wire. This could be circumventing the resistance to ground for the temperature sensor.

You do not have to be so elaborate to check this idea out. Just run a wire on the outside of the harness and hook it on one side or the other of the gray connector and see if it stops going to hot immediately.

So that my suggestion.

Phil

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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by aleekat on Thu Jul 27 20:59 CST 2017
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last visit: Fri Oct 24 13:19 CST 2014

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Everything I've read over the years stated 87 was the last year of the bad engine harness. It's worth a shot. That why I said look at the wiring.
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Post Back. That's whats makes this forum work.

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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by machine man on Fri Jul 28 20:03 CST 2017
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last visit: Wed Oct 22 15:40 CST 2014

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I agree with you.
I have read along with you too, but being the gospel, doesn't fly with me!

The trouble is with producing most cars they are divided up in mid year within only month numbers dividing the VIN. They just will not reflect all the changes with production.
Factory tags can note what supply vendors or when present stock amounts provided actually do run out but who has access to those?
This is why there is that fine print on remote pages of documents saying " subject to changes in production for product improvement changes."

We all live with day to day changes in our lives, so we cannot expect less OR when biodegradable wires stopped. (:-)
Sometimes I think, but cannot prove it, that the early strong engine cleaners soaked the wiring as it stayed in the harnesses.
It can just as easily not get rinsed out. Add on engine heat and there we are bad wiring.

Only an idea though!
Phil

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Temperature gauge goes to hot when the ignition is turned on and the engine is not running 200 1988

posted by aleekat on Thu Jul 27 16:23 CST 2017
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last visit: Fri Oct 24 13:19 CST 2014

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Wiring to the single wire gauge sensor. The other one is the ECT. Has no affect on the gauge.

https://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#TemperatureGaugeFluctuates
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