We bought a 91 XJ Laredo yesterday for $900. It's got 180K miles, automatic, 4.0, and at the time of picking it up, wasn't leaking anything. We're in Boise, Idaho so it's a zero rust Jeep.



Engine ran very smoothly, no exhaust leaks, transmission shifted flawlessly, was feeling pretty confident about the condition of the rig. After letting it sit a couple of hours without observing any leaks, we took it up to the foothills behind our home to test the 4x4 in some gravel.

Shifted fine into part time and full time, was really impressed with the suspension going up the hill, when suddenly we started experiencing violent vibrations. It was obvious the engine was unhappy so I immediately parked and turned it off. Steam began rising from the engine bay, got out and observed a significant amount of coolant had puked out the front grill and soaked the gravel below. Just to check, I tried moving the key to crank but nothing happened.

We waited a few minutes and were able to start the Jeep but had really weak cranking, turned it around the hill to get momentum going back down, and cruised home with the engine off in neutral. That was yesterday afternoon and it hasn't been able to start since - no cranks when turning the key, so I'm taking today to run through all of the typical checks (http://www.jeepforum.com/forum/f11/s...ation-1145815/)

With the violent vibrations and coolant only at the front of the block my assumption is a bad water pump? A mechanic friend of mine said the clutch fan can be suspect in this kind of situation as well. A bit puzzled as to why it won't crank now, but I suppose my neutral safety switch could have gotten stuck or my starter incidentally died at the same time.

Is there something more critical or drastic I'm missing here? Any thoughts/suggestions would be greatly appreciated. Naturally my girlfriend is pissed that the Jeep broke down the same day we bought it

 

Hopefully some experts will chime in because I am curious as to what they say. I would start with basics such as checking the battery with a multimeter, check the starter and pressure test the cooling system to see where the leak is coming from. You can "rent" those for free at Autozone or borrow one from your mechanic buddy. And yes the fan clutch is known to fail and is often a suggested maintenance replacement part. Was it running hot at any point prior?

 

Good move. Maybe too late, but certainly the right thing to do.


Good. Start with compression.



No. The coolant... possibly. More likely it's the radiator.


He's an idiot. (Most 'mechanics' are.)

Neither the fan clutch nor the water pump are going to give you "violent vibrations" or interfere with starting the engine.



Theoretically possible, but there is a much simpler, and far more likely explanation for all of this:

You overheated and trashed the engine.

Did you look at the temperature gauge during any of this?


Check your compression. I'm betting you'll see very low compression on most cylinders.

 

I'm interested in proactively replacing any part that commonly fails, in the interest of reliability for the future. Thanks for the suggestion of the pressure test. It would seem the leak is coming from the upper corner on the passenger side of the radiator. I suspect there was a pre-existing crack that was exacerbated by driving on a bumpy gravel hill. Perhaps with the high pressure of overheating combined with a crack being weakened, coolant burst through the radiator onto the fan and puked out the front grill.

I wasn't really paying attention to the temp gauge as I was on the gravel road, but it was in the red when the vibrating began.

 

I think we shut it down quickly enough. The vibrations were noticed immediately and only continued for 5-10 seconds at which point I pulled over and killed the engine.

Testing compression tomorrow.

I think you're right. After we got it started again today, idled and revved the engine for a few minutes until it was at operating temp of 195-210. It was running smoothly and sounded good, so we drove it around the block. It quickly overheated after about a minute of driving, was up to around 240 and a little steam was already protruding from the passenger side of the front of the engine bay. A quick check revealed coolant leaking from what seemed to be the top passenger corner of the radiator. It would seem a radiator replacement would be prudent, but while I'm at it I feel that replacing the water pump would be worthwhile for reliability's sake.

He was saying that the fan clutch can cause the fan to go awry and damage the radiator, causing a coolant leak and inevitably vibrations from overheating the engine. Sorry, I could have been more clear about that. Evidently he has encountered that scenario with these XJs a few times.

I wouldn't expect that a water pump or fan clutch could interfere with the starting system of a vehicle. Why do you say that a water pump couldn't be the cause for the vibrations of the engine? If the water pump was bad, not pumping coolant through the system properly, then that could lead to overheating and thus the vibrations, right?

Would you expect an engine to be trashed with only 5-10 seconds of vibrating before being shut off? I've only overheated an engine a couple of times before, always without damage incurring and addressing the issue immediately, so I'm pretty unaware as to how drastic the damage can be from it.

Ran through the typical no crank situation tests, determined the starter was bad. After swapping a new starter in today, the Jeep fired right up. I tossed a gallon of coolant in before trying to start it, and didn't see anything leaking... However after letting it idle up to temp and driving around the block, I did notice coolant leaking out of the corner of the radiator, and it was beginning to overheat.

In other news, I also noticed the electric? fan shroud had a chunk missing from it, which happened to be sitting on top of the intake.



The fan blades were a bit chewed up and one had a chunk missing from it





What would have caused this to happen? Just a slightly misaligned fan and a bumpy gravel road combining to raise a bit of havoc? Do I care about this at all?

So on the replacement list it's starting to look like:

-Radiator
-Thermostat
-Water pump
-Fan clutch
-Electric fan/shroud?

 

check engine mountings and any foreign material around fans / belt area

 

^This, it is possible you engine mounts failed (common on XJs, the OE mounts are pretty weak, and cheap aftermarket replacements even more so) which can cause the pulleys to hit the electric fan, and the clutch fan hit the radiator, both of which can cause scary noises/vibrations and possibly knock a hole in the rad.

 

That seems to be the most likely explanation, and I could be wrong but the engine mounts appear to be fine, bolts weren't loose, didn't find foreign material around the fans when I was in there besides the broken electric fan blade. I'll have someone with more experience than me inspect the motor mounts.

Anyhow I got some new parts in the mail last weekend:



-water pump
-thermostat
-temperature sender sensor
-fan clutch
-electric fan
-belt
-upper/lower radiator hoses
-not pictured is a new radiator

Installed everything and the cooling system functions properly now.

After first reassembly and filling the radiator with coolant, a leak began to spring from the thermostat housing. Took it apart, bought another new gasket and this time used permatex thermostat housing make-a-gasket sealer. Put it all back together again and the transmission to radiator ?quick connect? was leaking tranny fluid. It seemed the old plastic assembly was simply shot and not a great design, so I used new hosing and hose clamps instead. No more tranny leak.

Jeep fires up and immediately noise is coming from the engine bay because the radiator fan is hitting the front main seal? The seal around I believe the crank shaft pulley. I noticed when we purchased that the seal was somewhat oblong, protruding more on one side and more flush on the other side. The fan wasn't hitting the seal before though, but I did also replace the fan clutch.

I simply trimmed the oblong bit of the seal back a bit so the radiator fan wouldn't hit it. Then the Jeep ran smoothly and maintained temperature well... no leaks. However I'm guessing that seal is something I need to address.

 

You might mean the harmonic damper?

 

The fan can't hit the front main seal. Maybe the harmonic balancer as KGM said, but that seems very unlikely. Can you see what it's hitting or just guessing that it's hitting something? If the fan is hitting something I suspect you didn't get the clutch installed squarely, recheck the 4 nuts on it. Or maybe it's hitting the fan shroud.

 

Yes.. I believe it is the harmonic balancer. So the harmonic balancer makes up the outer rubber bit around the lower most pulley, which I assumed is the crankshaft pulley?

I was able to move the fan and see that it was indeed actually hitting this rubber bit and that was causing the noise. I could see some of the rubber was unevenly protruding on one side from its housing, and after trimming it away the fan doesn't hit it or make any sound anymore.

Here's a couple of pictures. You can see how I trimmed at it. Assuming it's best I just replace the harmonic balancer in its entirety?

As far as the fan clutch goes, it's possible it isn't quite square. I'll try reseating it. I can see when I spin it that most of the blades come within a millimeter of the rubber but one or two are a couple of millimeters off. Still though, the rubber itself was not evenly seated so only on certain revolutions would it hit the fan. I don't have a shroud on my radiator fan... Is there supposed to be one?

 

Your motor mounts or trans mounts are probably shot (if the fan clutch is installed squarely), the fan should be much further from the harmonic balancer.

 

If you have a suitable sized pry bar, get in between those motor mounts and try and pry the motor up. Just be careful what you pick to pry on for leverage. Tranny mount can be looked at the same way.

Mechanical fan does have a shroud or did. Might be a wrecking yard part only though. It is designed to have a shroud to channel that airflow. But if your motor mounts are bad it will tear it up again so mount check first.

180k is just a baby, good find.

 

$12 on Rock Auto for a mech fan shroud. Critical component to proper cooling, otherwise the fan just keeps recycling air around itself instead of really pulling air through

http://www.rockauto.com/en/moreinfo....=1315943&jsn=8