Another Cooling Question

OK, so here is my delimma... I have a 97 XJ (4.0) that I have had constant issues with due to it not liking to get hot in the least bit... It has never boiled over, but when the temp gets up to 210 (well below the redline) it starts acting real funky... Sometimes it will die, other tiimes it will idle erratically, other times it wont start back up after you shut it off etc... I have pretty much completely rebuilt the entire cooling system over the last several years... New water pump, all new hoses, flush & fill, tried Redline water wetter etc... Finally last fall the old radiator cracked and I replaced it with a new 4 core aluminum unit and continued to have issues... So then I started thinking it was something electrical that was heating up and going haywire, so every sensor and every relay is new as well... I have zero issues in the winter, but as soon as the outside temps rise above 75, bingo I have issues... So yesterday, I was driving and had one of the classic issues (all the gauges in the dash bouncing back and forth all crazy, running like it was firing on 3 cylynders and it just dies)... Let it sit and cool off for 10 minutes and it cranks right back up and acts like nothing ever happened, 15 minutes later after it heats back up same thing again... Its baffling me.... So yesterday I get it home, the engine is up to operating teperature (remember I have never had a "steam" blowing overheat) and I decide for whatever reason to check my antifreez levels... My new radiator has the old style cap with the pressure relief lever on it.... Outside of my better judgement (but something told me to check) I craked the pressure relief and nothing, no pressure, the radiator and hoses are too hot to touch for long but no pressure.... So then I opened it all the way and nothing, radiator and engine hot, but no pressure.... I took off the cap and the radiatior was full of coolant and the recovery tank is at the proper level too, the heater works etc... Im thinking thermostat at this point, but if the thermostat is not opening and the water is not flowing why is my temp gauge not pegged out??? I then checked all around the block and the head for signs of a water leak and nothing, dry as a bone... Thanks for any help, oh and I think Ill replace the temp sender also, looking into hood vents also... Just putting this out there to see if anyone else has any other clues....

Change you brain patterns. Your problem is not overheating. If it was, you would have pressure and steam. Not boiling = not overheating. You should have pressure in your system. You probably need a new radiator cap. Don't get the pressure relief kind. You shouldn't be opening that anyway. Have you tried pouring water on your Crank Position Sensor to cool it off when it runs bad or won't start? It is common for those CKP's to go bad all the time, especially heat sensitive. One guy convinced himself to get a new one because it would run good after he poured water on it to cool it off, then it would get hot, stall, and so on.

Maybe more than one thing going on here.

x2 on winterbeater's observation, you gotta have pressure in the cooling system, and it sounds like the cap is the best place to start on that.

It sounds like a failing CKP, and trying the cool water trick should give you some indication there.

Thanks for the replies guys...

I knew it was not a cooling system overheating issue, but I only get the issue when the engine temps climb above 210 (cooling system is fine but something does not like the heat)... I put a new CPS on it about 3 years ago, but I will definately try cooling it off, I'll try anything at this point... The cap is a new 16lb cap but it is the pressure relief type, it came with the new aluminum radiator i put in last year... I'll go get another one (there relatively cheap)... I'm also putting in a new thermostat just in case, there also inexpensive and replaced quickly...