0331 cylinder head - how serious?
 

Hi guys, I believe I have a cracked cylinder head because I've been losing coolant out the with no visible leaks, along with P0303 code (cylinder 3 misfire) on my CEL. I have a few questions..
1. How serious is a cracked head? Should I get it fixed ASAP or can I wait it out for a while (not what I'd like to do cause I feel like it'd get worse).
2. How else am I able to test to see if I have a cracked head? I've done my own observations and I've checked to see if there was any coolant in my oil but I don't think I saw any.
3. Also, how hard is it to replace? I'd prefer to do it myself than to take it to the shop.
4. Any direct bolt in replacements?

Thanks in advance.
PS. 2001 Cherokee sport, 4.0L straight 6..

Coolant is corrosive to bearings at even low levels. How much coolant are you using and how long to you plan on keeping the vehicle? Oil analysis will tell you what your bearing wear is like. Keep in mind with a crack, it could suddenly get bigger and your coolant loss could increase significantly all of a sudden. If the vehicle is a keeper, you should replace the head. There are many threads about this on almost ever Jeep forum out there. 02+ 0331 TUPY heads corrected the casting issue that causes the problem while other sources such as Clearwater Cylinder Head, ACH/ProMAXX, National Cylinder Head, etc. all sell beefed up heads that are bolt on replacements. It can be a DIY project if you have decent mechanic skills. About the only special tools required are a 12 point 1/2" drive socket both 3/8 and 1/2 drive, a torque wrench or torque wrenches capable of torquing at 22, 45, and 100, and 110 ft lbs, and a 3/8" universal with a good selection of extensions to get at the manifold bolts.

1) It is very serious. DO NOT wait! if you keep driving it and water get's into the oil you will cause bearing damage and that would lead to a complete engine rebuild.
2) you can do a compression test on all cylinders.
3) not to hard if you have help and know your way around an engine.
4)a 0331 Tupy is a direct emplacement.
The main thing that you need to do is start all of your testing and do not drive it or run the enginr or you will be have to do a rebuild.

Well, I noticed this about a month or so ago when I was parked out in the parking lot at the food store, came out and saw coolant dripping from my engine mat and I thought it was my radiator, but it wasn't. I didn't lose that much at that time but I was still skeptical. Recently I had to fill my coolant bottle back up to the fill mark about a week ago.

Gah, looks like I'll be doing it very very soon then. Seems like I'd be able to do it though, how would I go about doing a compression test on my cylinders? What results would I be looking for?

The unexplained coolant loss where 0331 heads have cracked and coolant is going into the crankcase (oil). If its dripping off your engine mat check the water pump area and lower radiator hose.

Checked that, there was a little bit of residue under the thermostat housing and I wasn't sure what that was from - I tightened up the hoses as much as I could and that went away, but I am still losing coolant

The welsh/freeze plugs could be leaking. There is a row of them under the exhaust manifold and one on the back of engine block (there are three back there but only one with coolant behind it). When the rear one leaks it dumps coolant into the bellhousing where it will only drip after sitting for a day or two. Otherwise the coolant in bellhousing evaporates or gets dumped out when driving.
My disappearing coolant issue turned out to be the rear coolant plug. Had to drop the tranny to replace it.

BEFORE you go any further do an oil analysis to see if you have any coolant in the oil. I was losing coolant with no visible signs and my first suspicion was the head...it turned out to be a bad water pump. There never was a coolant drip on my garage floor so I assume it was leaking at highway speeds.