Thermostat gauge fluctuating

[Crikee02]

I have an 89 Jeep Cherokee and the thermostat gauge is fluctutaing rapidly. The gauge will go all the way to hot and then down to cold quickly. I just got my cooling system flushed out and a new thermostat put in and right after I got this done I noticed this problem. Does anyone know why my gauge would act like this?

[72mino]

Your temp sending unit could be going bad or you could just have a loose wire. My wife's 96 cherokee's oil pressure guage will be pegged at 80 psi somtimes, but I tried unplugging the wire from the sending unit and it stayed pegged. I would guess the temp guage would work the same way.

[AlohaBra]

On the 96...a peg is a grounded wire...disconnect should be zero.
Same for the coolant gage sender on the 89..post...
On the 89, try to remove the sender and bleed the air out...otherwise replace it.


On the 96..if you disconnect the wire and it is still pegged...you need to look further....maybe at the gage pack and the wiring.

I used to have diagrams, but right now I can't post em...(website is down).

[Crikee02]

Well here, now I have a more exact question: If you have air in your coolant line would that cause your gauge to fluctuate rapidly? I only ask this because I took my car to an auto mechanic to have my cooling system flushed out, and when I got it back the gauge was going crazy. I told them about it and they told me that it was "just a gauge problem". This does not sound right to me. I am not an auto mechanic but I know my fair share about cars, but my car before this was a 76 VW bug, I never had to deal with this problem. So now my Jeep is completly messed up, and I just want to make sure that this can happen due to air in the system before I go and approach them......you know how some mechanics are. If you or anybody else would know I would greatly appreciate it.



Pamela

[fredjacksonsan]

Originally Posted by Crikee02

Well here, now I have a more exact question: If you have air in your coolant line would that cause your gauge to fluctuate rapidly? I only ask this because I took my car to an auto mechanic to have my cooling system flushed out, and when I got it back the gauge was going crazy. I told them about it and they told me that it was "just a gauge problem". This does not sound right to me. I am not an auto mechanic but I know my fair share about cars, but my car before this was a 76 VW bug, I never had to deal with this problem. So now my Jeep is completly messed up, and I just want to make sure that this can happen due to air in the system before I go and approach them......you know how some mechanics are. If you or anybody else would know I would greatly appreciate it.


Pamela

It's possible. Try opening your radiator cap (when it's cold), start the vehicle and put it on an incline with the front end about 6" to a foot higher than the rear. Turn the heater on full. Let it run for awhile, and keep the radiator filled. If you have air trapped in the system, you will see the level in the radiator drop periodically.

After about 1/2 hour it should cycle enough to get all the air out, if that is the issue.

[gtmud]

Of your mechanic flushed your system and didn't pay close attetion to the type of cooling system you have then air could be the issue. Especially if the guage workd fine before the flushing. Another way would be to undo the upper Rad hose from the T-stat housing. Oh I just realized, when he replaced your T-stat, were did it come from. Most stores ie. Advance auto and such only sell the T-stat with out the "bleeder" valve in it. The Bleeder valve is a little ball that should be in the top (when installed) of the T-stat that helps air to travel out of the system. If he didnot install this type or even drill a small hole in the T-stat flange to allow the same effect, than this is were your problem lies.
If you still need to bleed the system then remove the upper Rad hose from the T-stat housing, raise it up and pour in water/coolant mix untill you see a sollid stream of coolant coming from your T-stat housing. Reinstall your hose, top off the resivour and run the engine. this should fix it. That is if the T-stat was installed right. ( Also just keep in mind, just because its new, doesn't mean its a good part)

[AlohaBra]

I just remove the sender on the thermostat housing and wait until water-coolant comes flowing out and then plugging it. It cleans the thread of the sender also by doing this.