[masc]

Need help guys. I have a 98 TJ that has an overheat issue. Here is what I've done so far. All have resulted in either increased performance/driveability, but I am still running hot. Jeep is a 4.0l with auto tranny with about 105k miles.

This is my sons jeep, so I'm not exactly sure what indications led to the overheat, only the fact that it was overheating; all started beginning of June.

1. Changed T-stat; Stant 195 degree. no help. Gave it a fresh set of plugs, cap and rotor as well; no help.
2. Initial spin tests on fan clutch indicated it was okay.
2. Waterpump was not leaking, but decided to pull it; changed it. No help.
3. Radiator has leaked in the past, and was repaired with BAR-S. With the overheat testing it began leaking again and appeared to be a little corroded; changed it with an advanced auto replacement. This helped a little, but still overheated after about 8 miles in 90 degree weather.
4. This jeep has always run rough and was low on power. I decided to pull the head and have the valves done. No cracks, true surface. Valves were ground, head was cleaned up and new seals installed.
5. Since the head was off, I pulled the intake manifold and degunked all of the carbon buildup, cleaned the injectors; all looked good. Cylinder walls and piston tops looked great. Since I was in there, i decided to put in a fresh set of lifters as well. Re-installed, head and manifolds. Ran much better, but still seemed to be a low on power; still overheated; just took a little longer drive before she spiked into the red. Compression test at 150 psi on all 6 cylinders.
6. Now I'm thinking restricted exhaust. Had issues getting the cat separated from the muffler; make a long story short; new cat, new muffler, and tailpipe. It now performs like a jeep 4.0 should perform. Plenty of power; great acceleration. Still overheats.
7. Revisited the Fan clutch this morning. After a few turns with motor cold, I was able to spin it 6 or 7 turns freewheeling. Replace it this afternoon. Drove it about 14 miles. Initial tests with an obd scanner had the temps at 195 to 197. After about 8 miles, she went to 203 to 205. By mile 10, we were at 213. By the time we reached the house, we were at 226. Intake air temp was at 166; outside temp was around 90. It did not boil over this time and this is the farthest we've gone without a boil over, but I'm thinking that 226 is still way to high. I'm also thinking the intake temp is way to high as well.

Incrementally, all of the maintenance has either resulted in better performance or better cooling, but I think I still have issues.

Also did a snap down vacuum test this evening. Manifold vacuum at idle is steat at 13. zero at wot; increase to 28 with throttle released and then settles back to 13.

Any help is greatly appreciated. I'm truly out of ideas at this point.

Thanx,
Mike

[bonza]

I am wondering about your radiator. is it a three row, two row or single row?

I found that my stock radiator had partially plugged tubes directly in front of the fan clutch. besides overheating, as these tubes were plugged the air passing thru them was only ambient temperature and not the high temperature of the coolant. this in turn would not expand the bi metal coil on the fan clutch and activate the clutch thus making a bad situation worse.

found the radiator was plugged after immediately shutting down the engine feeling the radiator core with the palm of my hand. could feel the outer tubes were as hot as hell, but the inner tubes were all cool.
replaced the radiator with a new single row and no further problems

heep runs ok it hot weather and have driven in air temperatures as high as 50 degrees C (122 F) since without a problem

also upgraded to a seven bladed fan and extreme duty clutch for these extreme high air temps, but for your case this wont help.

[wushaw]

Will it overheat ideling? Have you pulled the lower hose to see if it has a spring in it?

[moonshinefuel]

Seems like you have done just about everything. This is an interesting mystery. You pulled the cylinder head a bit prematurely maybe, but you did rule that out, and did some repairs. I am thinking radiator, or some type of fluid blockage in or around the radiator. As long as your water pump is working fine, should be good there. I used to use stant termostats, I don't like them, I only use robertshaw thermostats now. That's just me.

[sduncan]

Since you've done everything and then some, I'm thinking its back to basics. Radiator, good cap, hoses collasping?? Did you really do a good flush to get ALL the radiator sealant you had previously put in it? Is the shroud in good shape?

[MT_Ranger]

Have your system checked for pressure leaks, including the radiator cap. Also, a flush of the cooling system wouldn't hurt.