i checked the radiator cap. it seems fine but i'm going to buy a new one anyway. i have been checking fluid levels every day,, twice a day. ran thru a bunch of diagnostics i found on youtube. according to those simple tests, my all components are in working order. so, the only thing i have yet to do is backflush the heater core. it could have clogged. i'm going to have it professionally flushed and the right amount of coolant and distilled water replaced friday. beyond that, i don't know what else to do. i've covered everything. thanks for all the suggestions. have been most helpful.

 

The rad cap on a open type cooling system is critical to the cooling systems overall performance. The rad cap contains 2 valves and 3 sealing surfaces. All 5 components must perform in precise harmony with each other.

 

I still need help. Flushed the system entirely, replaced the radiator cap. put 50/50 coolant in it. cranked it. took forever to heat up then went pasts operating temperature and the resevoir filled up to almost overflowing and I shut it off. is this the thermostat?

 

So I don't have to go back and re-read the thread, what cooling system parts have u replaced, other than the rad cap?

 

Not to be overly negative, but it sounds like my race car when the head gasket went. It was venting exhaust into the coolant passage in the head and boiling off the coolant. The top of the radiator, the top hose, and the overflow were boiling. The bottom hose and the bottom of the radiator were cool enough to put your hand on.

 

i think the thermostat is stuck. when i get on the interstate and really drive it, the temp gauge creeps up. if i turn on the heat, it goes back down. coolant is not boiled in resevoir. it was just settling in. also, when i drained the system, i got 3 gallons out. only put 1.5 back in. wouldn't take more. so this indicates a block. thermostat isn't opening. right?

 

No , water goes in bottom hose exits top hose once T stat opens . Air pocket maybe .
Have you replaced the T stat ?

 

replaced the thermostat. problems seems to have been solved. drove on interstate for 60 miles yesterday in the middle of the day. hot as hell. temp gauge stayed on 150. no leaks, no overflows. tested the old thermostat stove top in boiled water, did not open. problem solved. thanks for all the tidbits. helped mucho.

 

If it's really only getting up to 150 with a new stat, u have a hole new set of problems.

 

i had wondered. before these problems began it ran around hovered at 210. But, the thermostat said 160 degrees on the box so i'm assuming that's why. Maybe its the wrong thermostat. If it is, what are the implications and should i change it to a 190?

 

the engine is computed to run most efficiently at that temperature. if it runs at 150 steadily, it isn't going to perform as well as it should. it is a tough decision since the designed the optimal running temperature at such a close threshold to critical temp. regardless, you need to replace that thermostat with the correct one. if you are still concerned with a higher than desired running temperature after the new thermostat, add a LITTLE purple ice to bring the operating temperature down....but in a proper operating machine, you won't need it.

 

The t-stat does one thing and one thing only......determine MINIMUM coolant temp. All of the other cooling system components, their condition and driving conditions determine maximum coolant temp. A properly functioning t-stat will never be the sole cause overheating. Your minimum coolant temp is most likely 160+ using a 160 stat. Going by the factory temp gauge, determining 150 is a guess at best. The XJ left the factory with a 195F stat. The coolant temp range is 160F (where the ECU counts a warm-up cycle) and 218F (where the ECU turns on the auxiliary efan). My experience is, a 160 stat makes for a very weak heater and in regard to the XJ, a 160 stat could set a trouble code and check engine light.