~~Temperature gauge going up and down Hey all, I have just purchased a 1996 XJ with 225k on it ($1400)... I was like a little school boy to get in and drive it since it had been about 10yrs since my old '88 XJ.
At any event, I found that the RADIATOR had a leak, no biggie, I've replaced that before so I just bought a cheapo (on a budget) replacement, It will do for the time. At any event, now the temp gauge is going between 180 and 230 degrees. It takes about 2 min for the climb to 230 degrees then it takes like 10 seconds for the drop (I assume the electric fan is kicking on). I did replace the fan clutch as well while I was at it it seemed faulty, so not that, the electric fan is working fine as well. So I drove it about 80 miles on the freeway watching it go up and down up and down... I'm sure this would of given plenty of time for the bubbles to work their way out. So, the question...
What is likely to be causing the temperature fluctuations??
Thanks, Matt

 

T-stat, water pump, bad gauge, sending unit, faulty electrical connection, low coolant level? Got access to a infrared temp gun? Point it at the t-stat housing.

 

These are cheap to replace, especially if you do not know the age of these items check out rockauto.com for parts you can get a new water pump for about the same price as a reman from the big box stores. sounds like water pump possibly on its way out with the surging temp replace tstat while your at it cheap insuance, but faulty sending unit is well with in the realm of possibility like djb said verify with an infared temp gun.

 

I dont have a temp gauge on my Jeep but my Ram does that and its completely normal. goes up slowly, then quickly drops down when the thermostat opens. not sure about XJ's but it might be normal?

 

Should stay pretty constant once the thermostat opens and stabilizes.

I'd start with a new thermostat. I buy mine directly from Jeep as there are so many junk aftermarket stats on the market. I also like the Stant SuperStat.

195 degree only.

 

....yeah i dont have a infared temp gun... the temp. wasn't going up and down until i replaced the radiator as a side note.

 

For a 96, the system should "burp" itself with about 4 complete heat up / cool down cycles.

Have you done that yet??

Could be air.

 

No i have not gone through 4 cycles, just the one 80 mile trip home... I will keep an eye on it in the meantime, I was hesitantly thinking it might be the water pump, when my old one went out it started leaking so that gave it away, so not seen the other end where the temp will climb slow and then drop, so I will first go for the thermostat. Is there a post on replacing the theromostat / water pump?? I dont remember as well how i replaced the water pump. I know it wasn't too hard tho.

Thanks for all the input, you have all had great points, always appreciated.

 

Replacing the stat is never wrong, but until you get through at least 3-4 complete heat up and cool down cycles, you CAN have an air pocket in the system, and that would give you the symptoms you describe.

Give it a few cycles to see.

 

.......and keep an eye on the overflow bottle, needs to always have at least some coolant in it. With a good rad cap, coolant level in the bottle will rise/fall as the engine heats/cools.

 

Yeah djb, the coolant level was above full, I did that with the feeling that there would be some more coolant that would be sucked in, and there was, it is now right at the 'full' mark...
so now i will be working on the floorboards today...grumble, there is more rust than i thought, I feel like the Flintstones driving with the holes in the drivers floorboards. LOL

 

I replaced the thermostat and all is well. the temp. is staying at 200 degrees. thanks again for the help.