fluctuating temp gauge.

Just changed the water pump, thermostat, and coolant sensor in the thermostat housing. The temp gauge when warm, whether it's just idling or running down the road will get up to 210 then drop down to 170-180 before climbing back up to 210 and cycling back and forth. What could be causing this problem? Air in the system? bad radiator cap? Faulty gauge? bad temp sending unit?

Any suggestions would be great,

Sean

personally, i wouldnt be worried about it if it isnt getting above 210.... but thats just me

When you refill your coolent you will have air pockets in the water jacket that will cause small hot spots, and make your temp jump around. All you have to do is get it up to temp and cool it down then refill it a few times.
Good luck.:repair:

I have this exact problem in my 96 4.0 aw4 XJ. Temp gauges swings all around between 195 and 160/170. Every part in my cooling system is new, including my Robert Shaw 195* t stat, and both temp sensors.

No idea how to fix this problem, it is very annoying and bugs me a great deal.

I have had this going on for about a year now... I dont think it is related to air in the system.

Some have suggested it could be the ECM switching between open and closed loop modes.

hmm, i've burped the cooling system numerous times now, and even got a new rad. cap. Still fluctuating. Not too worried about it, it's just annoying. I also read that the fluctuation in temp can cause premature head warpage. Don't know about that one. Maybe if it got to like 260 then cooled way down....

my 90xj has always done this. so did my 88mj. i just assumed it was the thermostat opening and closing. never saw it as a problem.

Changed out the thermostat w/a 195* Superstant. Solved the fluctuation problem. Waiting to see if it took care of the start problem.....