Temperature gauge wierdness - temp reading high

[4wheelsgood]

About a week ago the temp gauge on my '88 4.0l started acting up. When it began, the needle would dip to the low range of normal whenever the RPMs exceeded about 2,000 rpm. It seemed like a possible stuck thermostat, so I replaced it with another OEM (195 degree) unit. The same problem continued, with the gauge acting more erratic - diving to 0 and moving way too quickly to reflect actual temp changes in the engine. But the gauge never went over 210.

I figured the sending unit was going bad, so I switched it out. Now the gauge acts "normal" (i.e., moves gradually up as the engine warms up, then hovers at a set temp). The only problem is, it sits well above 210, almost to the red zone. My engine has never run that hot, and I don't think it is now, because because my fan has always come on consistently at 210. The fan still cycles normally if I sit and idle long enough, so I know the temp reading is not accurate.

About the cooling system - it's a converted open system, with the fan switch in the original location on the radiator. Everything in the cooling system is less than 2 years old: radiator, hoses, water pump, and now the temp sending unit.

About the only thing left to replace is the temp gauge itself. Has anyone else had their temp gauge go bad on them, and start reading warmer? Could it be a bad ground somewhere? My engine is grounded well, but I am not sure about the dash. None of the other gauges is acting up.

Any ideas?

 

[winterbeater]

It might be worth it to pick up one of these ohm sending units like Wim has: http://www.naxja.org/forum/showthread.php?t=983528&highlight=temperature

 

[wim hoppenbrouwers]

Hallo. Like Winterbeeter says, you can test your gauge with different resistors or a device.
My problem was a cool engine, so I test the temp.gauge first.
60 Ohms resistor gives 260F and 100 Ohms gives 220F.
1365 Ohms gives 100F. 55 Ohms gives 260F These values were correct.



Put the resistor wire into the connector and the other wire to ground.

p.s finally, I changed the T stat. It was stuck open.

'92 XJ

 

[winterbeater]

Wim, I was searching for a "ohm generating device" like you used. I haven't been able to find one. Can you describe it by a manufacturer name or more? What type of store had it? Electronics, automotive? Thanks for the help.

 

[4wheelsgood]

It seems to me that "ohm generating device" is another way of saying "variable resistor."

 

[wim hoppenbrouwers]

Wim, I was searching for a "ohm generating device" like you used. I haven't been able to find one. Can you describe it by a manufacturer name or more? What type of store had it? Electronics, automotive? Thanks for the help.

Hallo. It is bought 4 years ago by a german electronic warehouse CONRAD.
(www.conrad.com) It's called:decadebank.
There is no brand name or specifications on it.
it contains 36 resistors (5 Ohm till 1 MOhm. 1/4 W max load. 10% acc.
I think it's coming from the far east.
You can make your own very easy with equivalent resistors. :dunce:

 

[veedubshafer]

hmm, I may have to invest in something like this - it would be nice to be able to test the accuracy of certain things

I was just thinking, you could get a potentiometer at radio shack and set the reistance with an ohm meter and then use it the same way...I might just go get one now!

 

[winterbeater]

hmm, I may have to invest in something like this - it would be nice to be able to test the accuracy of certain things

I was just thinking, you could get a potentiometer at radio shack and set the reistance with an ohm meter and then use it the same way...I might just go get one now!

My thought exactly. $3.99 at the Shack. Or maybe scrounge a volume control from an old TV or stereo.

 

[4wheelsgood]

Yes, potentiometer is another term for a variable resistor. As long as you have an ohmmeter to tell you how much resistance you have at different settings, then you are in business. And a volume control out of an old TV or radio would work great.

Now I'm going to take Wim's settings and test my gauge.

Anybody know how much work it is to swap out a temp gauge if that's what I need to do?

And by the way, where can I get some of that wood-grain stylin' for my dash?

 

[winterbeater]

I'm thinking you would need to replace the whole cluster if the gage was truly bad. I think that either your gage will check good, or its in your connections, which you can clean up.