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Soooo... the dreaded cracked head. My mom has a 2001 Cherokee, 4.0 L6. I am fairly positive it has a cracked head, as coolant is disappearing, and I looked through the oil cap and saw some green dots (green dye in her coolant) on top of the head. Also the oil pressure is low. We are going to have a compression test and leak down test performed for final confirmation. There was talk of improved cylinder heads available for her model in another thread I was reading, and I would appreciate some input on which are best, keeping in mind we are in west coast Canada, and therefore would appreciate a solution available here. Thanks for any and all help you folks can provide.

investinwaffles

Clearwater Cylinder Heads out of Florida has an "improved" head design with thicker casting between the 3&4 cylinders, where the 0331 head is prone to cracking. It is a brand new casting and now re-manufactured or anything

https://www.cylinder-heads.com/cylin...ms-fits-99-07/

I would see what shipping to Canada looks like for one of those. Or find a 0720 head (or any of the other ones that will work with an 01 XJ), and have it rebuilt locally. My local shop only charges $60 to hot tank (clean) and magnaflux the cylinder heads last time I checked

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Turbo X_J

A new cylinder head won't save an irreparably damaged engine. Low oil pressure is indicative of badly scored cam bearings.

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Turbo X_J

The 4.0 is OHV not OHC. Ethylene gylcol mixes with engine oil and forms an extremely corrosive sludge. In addition to plugging the oil pickup screen, this concoction eats the bearings then increasing clearances and finally low/no oil pressure.

investinwaffles

Coolant + oil is a terrible lubricant, many of the bearing surfaces could be worn irreparably.

Generally if you have good oil pressure, your bearing surfaces should still be OK. Check for gouging and pitting on the bearings though, and you can always rebuild a bottom end alongside the car, and swap cylinder heads once the bottom end is built. The 4.0 is not an interference engine so I don't really see any harm in running the new cylinder head on a "clapped" out motor?

A few oil changes with Rotella T6 should clear out most of the brown sludge I would think

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extrashaky

If you're seeing coolant droplets on top of the head, you have confirmation. There's no other way for those green coolant drops to get there.

Except it may not. A leakdown test can tell you whether there's a crack to the combustion chamber. The 0331 crack often doesn't reach the combustion chamber but just allows transfer between coolant passages and the top of the head. So don't be surprised if the compression and leak down tests come back okay, but you still have a crack.

How low is "low"? And have you verified that with a mechanical gauge?

The sending units on these things often fail to the low side, so there's always a possibility that the oil pressure is still okay. I'd verify it before sinking the time and money into replacing a bottom end that may not need it.

You might also see if the pressure comes up with a fresh oil change. The coolant in the oil itself can cause the pressure to drop. If you have had coolant in your oil, the bearings have no doubt been damaged, but maybe not to the point that you can't get tens of thousands of more miles out of it.

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investinwaffles

How long has it been drinking coolant?

Low oil pressure is going to be 5 psi and under at hot idle, verified with a mechanical gauge (remove the factory one an use a mechanical or digital standalone gauge for an exact measurement). If you have 10+ psi at hot idle (and I mean hot, like after a 30 minute drive minimum) then you should be in OK shape to just slap a new head on there. The dash gauge is not really that accurate in my experience

Changing the bearings is going to involve pulling the motor, and honestly I would rather build or source another used shortblock and swap if you want to go that route.

I unfortunately don't think most parts stores rent an oil pressure test kit. They have fuel pressure, cylinder pressure, etc but not for oil pressure IIRC

Here is a cheap kit that would do the trick

Turbo X_J

500 psi?
This may be a better option:

https://www.ebay.com/itm/Sunpro-Gaug...kAAOSwHQ9Wa7~c

investinwaffles

Lol, I didn't look that closely

Definantelly find one that is 100 PSI or so

extrashaky

That one is really made to mount under the dash, not to use as a testing gauge.

The simplest thing to do is to run down to your local Harbor Freight store and pick up one of these:

https://www.harborfreight.com/engine...kit-62621.html

I have one and can attest that it works fine. It has a five and a half foot hose on it so that you can plug it in, drape it across to the driver's side and watch the dial as you crank the engine. Mine included the fitting that fits our sender gallery.

That kit used to cost $26. Now it appears they have dropped it to $22, which drops to less than $18 with the 20% off coupon in practically every coupon mailer on the planet (ValPak, Red Plum, etc.). Or you can sign up for their emails and get a coupon. Either way, you're not going to do any better for under $20.

Turbo X_J

Correct.
This gauge can and should be mounted on the dash to permanently replace the notoriously inaccurate factory one.