overheated the heck out of a 4.0

new issue, new thread... hope that's okay guys =]

Ok, so while I wasn't believing the temperature gauge, the Jeep suffered an extreme case of overheat on a 70-75mph highway. Possibly had it in the red-zone for several minutes; can't be sure, since I'm still not sure of the accuracy of the temp-gauge. As I pulled off on an exit (almost to the parking lot of an auto parts store, as luck would have it), the engine died on its own (!) and let the steam out. Popped the hood after it cooled off some... not much coolant left in the system, antifreeze splashed all over the place, appearing to be mostly from the pressure bottle area (new Quadratec installed a few weeks ago). Not sure if it was a splash or a leak, but there was coolant on the block right under the head - and not on the head itself. Almost looked like it was leaking from the head gasket area; is that even possible? Was enough to make me too afraid to start it, anyway. It *does* still crank, I tapped it a few times with the starter, just enough to make sure it still turns.

Possibly related: Stopped a few hours beforehand, again unknown temp gauge reading, the engine was slightly over-idling - 1000-1100 RPM instead of the usual 700. I figured at the time I must have knocked a vacuum line loose somewhere while testing the TPS last night.

Since I was on the highway, my best guess is that the suction finally got to my lower radiator hose (no spring... gah) and closed it off, leading to the overheat condition. Not sure why today and not any other time, I've done the same 150-mi run 3 times since I replaced the hoses/bottle and no problems until now.

So now I get to assess the damage... first i'll check the oil, see if there's any coolant in there. Looked fine from the dipstick but I'll drain it all out to make sure. Maybe get a compression gauge and make sure the cylinders are still solid... anything else I can do? As long as the oil's clear, will it be safe to start? Never done a head gasket before, kinda don't want to start now.

It's a fair bet that you've blown the head gasket and coolant got into the combustion chambers causing the engine to die. Even if there's no coolant in the oil, you could still have a blown head gasket or worse, a cracked head. If the oil is clear and up to the mark, refill the cooling system with distilled water (no coolant) and start the engine. It'll probably run rough but it's worth a try since you might just be able to limp to the nearest repair shop.
Do a compression check on all cylinders to assess their state. Low compression on adjacent cylinders will point to the head gasket blowing between them.

Ya know, I'm just not going to question the Jeep anymore... the thing's a tank. Either that or I'm really lucky, kinda doubt it. Ran compression test this morning, 130-150 across the board. Dumped the oil, no water. So I started the thing up..... like nothing ever happened, it's running fine. Like it wanted to make fun of me for doubting it or something.

Replacing lower radiator hose with a spring-included model on Monday, soonest the dealer could get one. Probably killed the t-stat so that'll be swapped too... OEM dealer part. No clue on the fan clutch, since there seems to be no concensus on the testing method, so I'm debating whether to put one of those in too.

And I'm gonna fix the d4m* temperature gauge so this never happens again.

As always, thanks for your help everybody... (both threads)