anyone with this cooling issue?

87 cherokee, converted to open system and has a HO block so the temp gauge sender was moved up to the T-stat housing. My temp gauge will rise normal, and then proceed to move up and down anywhere from 170 up to a little past 210. The temp rises and falls faster when im at highway speeds, and barely creeps when im at a stand still. These are the readings I get with a new sender...the old sender did the same thing, but would read from 150 to about 200 max. I have a new radiator, water pump, now all new sensors, rad. cap and thermostat. Ive actually been through about 3 thermostats and 2 caps...Im about to beat my head agains a wall!! I thought that maybe it was due to the relocation of the temp sender directly in front of the T-stat, but it never used to do this until recently. Ive even replaced the wire from the sensor up to the firewall because it looked kinda worn and ugly. There are no visible leaks, no coolant missing (nothing in the oil), it seems to build pressure fine, and the heater works like a charm...I just cant figure out the gauge. Anyone else have this issue or have any ideas?

Thanks,

Me

How are the other guages working?
Could it be a gauge grounding issue?

Have you ever done this? Every Renix era Jeep needs it done.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

Is it fluctuating temp due to the thermostat opening/closing?
What's wrong with the HO sender location on the back of the head?

Ive redone the grounds, and the other gauges work perfectly. There is no HO sender location on the back of the head, I would have had to drill and tap it in there. I guess it could be from the thermostat opening and closing, but it never seemed to move before when it was in that location...just all of the sudden started doing it.

With the sensor where it is, you should expect to see large fluctuations in the temps when the thermostat opens and closes.

stock type radiator and fan setup ???

X 2 on checking & cleaning wiring and connections.

Double check the coolant level ... 12qts is the minimum.

The temp sensor is mounted in the heater hose gallery of the thermostat housing ...and a high point in the cooling system.

Air pockets can cause temp fluctuations as the sensor needs to be "wet" for correct readings.

Whats the breed of thermostat ??? ... If it doesnt meter the flow properly and just flip/flops - from fully closed to fully open - then it may be a cause of your issue.

If the t'stat is working properly ... then the factory gauge wont even register the few degrees, temp variations, that occur during normal driving at operating temp ...