4.0 back from the dead?

[DIRT_NASTYY_]

This is the 3rd Jeep I've owned with a 4.0, and after my trip to Death Valley last weekend I am convinced these motors enjoy abuse or something. 

 

I drove my Jeep out to Death Valley with a group of people, and on day 1 my friend sheared the bolts for his engine mount brackets on his XJ going down a washboard road. We have no idea why it happened, but it was getting late and we were about 2 hours into the desert so we decided to camp near that spot and tow him out the next day. 

 

After some breakfast and close exploring, we hooked up his Jeep and I tried to pull him uphill and out of the valley. Between the 100 degree temperature and the fact both our Jeeps were loaded down with camping gear, I should have known better than to try it. I made it about 4 miles when steam started pouring out from under the hood (the "dummy light" for temp never went off). We pulled over and coolant was bubbling out of the reservoir so we let it cool down. When everything seemed fine I tried to pull his Jeep again, however under load the motor started making a terrible knocking noise.

 

We decided to unhook his Jeep and come back with another vehicle later. After my Jeep cooled off again everything seemed fine and I proceeded to drive up the hill, however 2 miles later the knock came back with vengeance and when I pulled over the motor completely shut off and wouldn't even crank over. I open the hood and coolant was pouring out the reservoir and head gasket, oil was coming out between the engine and trans, and smoke was coming out of the oil fill cap. I figured the motor was just pushed too hard at 180k and it was toast. We loaded up into the 2 remaining cars and proceeded to drive into town an hour and a half away. 

 

So at this point we are driving into Lone Pine, calling and texting everyone we know trying to cash in any favor we had. My buddy reaches out to a few people on IG and finds someone who was willing to come save us! His username on IG is 4lowlance and he has a bitchin full size cummins. He happened to be on his way back from a trip in Utah and was passing by on the other side of Death Valley and took a detour to come pull us out. He got into Lone Pine around 10pm, and we hopped into the truck of a guy we've never met, just know from IG for the last 8 years or so, and everyone else stays back at a hotel in town. 

 

We drive nearly 2 hours out into the desert, talking and laughing about the situation to pass time. Eventually we pass my Jeep and get to my friends XJ. As we come back towards my Comanche while pulling the XJ, it's about 1AM and he decides the air was cool enough outside to try and pull BOTH our Jeeps at the same time. We hook a strap from the back of his truck to the front my fiends XJ, and the back of his XJ to the front of my MJ. We spend the next few hours just cruising slowly for about 5min, then stop and let the cummins take a break, then start cruising again just to ensure we don't get a 3rd vehicle broken. After a few hours we finally make it over the mountain, and start proceeding downhill. This proved to be tricky while double towing as we both couldn't keep the straps tight at the same time. 

 

We stopped to figure out how we can do this more efficiently, when our new friend asks if I have tried to start my Comanche after it died on the trail. I told him I hadn't, but we start thinking it might be helpful to see if it will run and just putt it to the downhill sections to coast. We check the fluids and nothing is cross contaminated, and I figured if the motor is toast then the motor is toast. I also have another 4.0 on a stand at home I can utilize if the block gets damaged badly enough. After checking everything we go to crank it and it fires right up, no leaks or knocking noise. I hopped right in and decided to see how far I could make it before something goes wrong. 

 

It drives the last 30min with no issues, and makes it to the pavement, and while I wait for the other 2 to catch up I top off the fluids and let it idle while I inspect the head gasket and other areas. They catch up to me and we are all dumbfounded that it's still running with 0 issues, and we head back towards Lone Pine. We get about 15 miles from Lone Pine and at a highway junction,  I tell 4lowlance that I can pull my buddy the rest of the way. At this point he's been up for like 36 hours (remember he was driving back from Utah when he came to help), and if anything happens we can get towed back home since we are on pavement had have cell service now. We part ways and thank him immensely for saving our butts, and I pull my buddy all the way into Lone Pine and we park our Jeeps behind the hotel. At this point it's 5am, so we get a few hours of sleep and then figure out where to go from there. 

 

In the morning I go through all the fluids again and everything seems fine, nothing had leaked in the parking lot, and the motor was sounding healthy. My fiend gets a towing situation setup for his XJ, and I start making my way south on the 395. My truck cruised at 65mph the whole way home (2 hours) with no issues, no noises, no leaks, nothing. We get it in the shop and start going though it, still no cross contamination of fluids and all cylinders still held compression. I've never seen a motor pushed so hard, and decide to work fine out of nowhere like this. I'm going to be swapping in the OEM cluster with actual gauges sooner than later and will add some oil coolers I have laying around, and I might repair the head gasket just for insurance. 

 

All in all this was a different kind of adventure than I intended to have, and it was one of the trips where everything just went wrong and all we could do was laugh. 

 

[87MJTIM]

I've heard others say that you can try to kill a 4.0, but it will fight you.  Sounds like yours fought back...and won.

[shelbyluvv]

My daughter just blew up her 4.0 in the 99. It was so hot that 4 hours later it was still 190°! Needless to say it killed the lifters and bearings.

I had a parts rig and yanked to motor and trans. She cooked the torque converter also. Then I put it in her 99. I drove the donor to where I pulled it and the oil pressure was perfect. After I installed it the Jeep had no oil pressure?

Easy, the sensor went bad. Swapped sensor still no oil pressure. Drive Jeep around for about 20 minutes and all seems fine. No ticks, knocks or rattles. Must be a wiring issue. Had to of pinched the harness when installing the engine and transmission.

She drives it the next day (Friday) 86 miles round-trip to work and back. Still runs great. Saturday morning I wake up and go buy a mechanical gauge just to ease my mind. Hook it up and start the Jeep. NO OIL PRESSURE! None!

Pull the pan and find the pump is broke right between the mounting holes. I pulled the pump out of the junker and toss it in. Button it up and now it has oil pressure. She drives it every day and has put 2000 miles on it since I swapped the engines.

To say a 4.0 is a tough dude is an understatement. They are amazingly well built engines!

[DIRT_NASTYY_]

1 hour ago, shelbyluvv said:

My daughter just blew up her 4.0 in the 99. It was so hot that 4 hours later it was still 190°! Needless to say it killed the lifters and bearings.

I had a parts rig and yanked to motor and trans. She cooked the torque converter also. Then I put it in her 99. I drove the donor to where I pulled it and the oil pressure was perfect. After I installed it the Jeep had no oil pressure?

Easy, the sensor went bad. Swapped sensor still no oil pressure. Drive Jeep around for about 20 minutes and all seems fine. No ticks, knocks or rattles. Must be a wiring issue. Had to of pinched the harness when installing the engine and transmission.

She drives it the next day (Friday) 86 miles round-trip to work and back. Still runs great. Saturday morning I wake up and go buy a mechanical gauge just to ease my mind. Hook it up and start the Jeep. NO OIL PRESSURE! None!

Pull the pan and find the pump is broke right between the mounting holes. I pulled the pump out of the junker and toss it in. Button it up and now it has oil pressure. She drives it every day and has put 2000 miles on it since I swapped the engines.

To say a 4.0 is a tough dude is an understatement. They are amazingly well built engines!

 

That's gnarly, I blew out the crankshaft bearings in my last 4.0 from an oil pump going bad,

Sounds like she has a bullet proof 4.0 in that thing!

[Minuit]

Nobody told the Jeep 4.0 that pansy things like oil pressure and a functioning cooling system are needed for an engine to run. My 89 idled for 10 minutes with no oil flow at all before I noticed that it sounded a little clackier than usual (I also assumed that my aftermarket sender crapped out). Doesn't seem any worse for wear after that. Rebuilding the pump even brought the pressure at hot idle to within factory spec!

 

I will definitely be trusting the oil gauge a little bit more now.

[cruiser54]

Here's why the bolts broke off:

 

Beginning with the HO blocks in 1991, the factory did not tap the holes deep enough.

Therefore, you had tight bolts not clamping things together. So, they broke off.

 

 

 

[Jeep Driver]

Nine lives............you just killed number eight. 

[ftpiercecracker1]

I can attest to this too. I was forced to drive mine until the engine seized. Came back the next day and she fired right up.

 

That was 75k miles ago.