I posted in the Explorer forum of my current problem, but I think this forum may have more people familiar with the OHV 4.0L.

I have a '93 Explorer with 205,000 miles. A while back my mother-in-law was driving it, and called me saying it was hesitating. I checked it out and did not see anything, so I drove it home (<40 miles on the freeway). Hesitation seemed kinda bad at times, but the engine was not stumbling too badly. As I was going up a hill the tranny kicked down, followed by a loud explosion as the muffler exploded. The hesitation seemed to go away, and I made it home.

At home I found a plug wire off (#4). I replaced the plug wires, but then did not drive it for about a year. Now when driving I noticed the temp guage cycling between almost hot and then near cold. I serviced the cooling system with new hoses, t-stat, and water pump since the mileage is so high. The guage is not cycling as high, but it is still flapping up and down. I do not see any bubbles in the radiator, but I seem to be building pressure in the cooling system. I have tried my best to burp it, and I do not believe there are air bubbles.

Went ahead and did a compression test and found
#1 - 165 psi #4 - 160 psi
#2 - 180 psi #5 - 190 psi
#3 - 180 psi #6 - 185 psi
All of the pressures seem to be okay, and the only anomaly I found was oil on the #6 spark plug when I removed it.

I sincerely apologize for the massive post, but I would hope that I could get as many suggestions as you all can offer.

Thanks,
Mike

 

I had a similar problem with the cooling system on my 94 4.0 OHV and found it was the heater core was almost plugged all the way. The 4.0's use the heater core as a bypass when the thermostate is closed and if it isn't flowing enough your guage will cycle. It will also cycle if it has an air pocket, but you said you already did the burp thing.

One of the clues on mine was when i was trying to burp my system with the rad cap off every few minuts it would throw about a quart of coolent out due to very slow cerculation. I also was not getting very much heat.

From your vehicle sitting about a year it's possible alot of gunk settled in the core, I tried back flushing mine but ended up replaceing it and all was fine.

You can also feel the heater hoses as the vehicle is warming up, One should not be coller then the other.

 

i am wondering if you are getting a odd almost slufer smell in the exhaust? i had a 99 with the same problem. i also had the same heater core problem. so i changer the core and it did not fix the problem. the compression in all clyenders were within spec but come to find out i had a blown head gaskett. .. go figure. so i took the head off and did the job. all fixed. i only did the top end rebuild not a bottem end. but i did not trust the truck after that so i traded it in for my 04 fx4 . good luck