What 4.0 heads are more prone to cracking?(and other head questions)

Ok, I was at the dealer today ordering a head gasket and other related parts when the parts guy (seems pretty knowledgeable) reminded me that it's possible that I have a cracked head. He referred me to a couple reputable shops where I could have it checked. I'm going to have it checked for sure, but my question is: which year(s) 4.0 heads were alot more prone to cracking? If memory serves me, I thought it was the 2000 and newer ones. (I have a 98) But I was still wondering...

The engine has been overheated once (lower rad hose came off and let all the water out) But it all happened within a mile or so of my destination, so I don't think anything got TOO hot; the outside temp was in the mid 30's. After I reconnected the hose (with real clamps) and filled 'er back up, she fired right up without any hesitation, and has been trouble free ever since.

The reason I'm changing the head gasket: For as long as I've been getting my oil analyzed, there has always been slightly higher than average potassium and sodium levels in the oil. (Sodium and potassium are distinct signs of antifreeze in the oil) There were no distinct changes on the oil that was in for the overheating. But over the past 20k miles or so, the potassium and sodium numbers have been steadily increasing, and on the last analysis they were high enough to be sure that there was actually antifreeze in the oil. Hence the planned change of the head gasket...

Anything is welcome here...

TIA

-Chad

If you have the cooling system pressure tested, that should reveal if you have a coolant leak past a defect in the head gasket or through a crack in the head.
You lost all your coolant from the lower radiator hose so there was nothing left to cool the head. It's quite likely that it's either warped or it has a small crack.

Eh, thats what I was afraid of hearing. I guess I'll just have to wait and see when I pull it off.

I'm still a semi-newb when it comes to internal engine work, so I have a few more questions: Now if the coolant is leaking across the gasket between the head and the block, will it be easy to spot once the head is removed?(Like some kind of build-up or sludge where the coolant was mixing with the oil?) If the head is slightly warped, it can be machined flat again, right? Can a machine shop also check to see if the head is cracked? What all is involved in that?

Any help is appreciated here guys!

-Chad

98JeepXJ said:

Eh, thats what I was afraid of hearing. I guess I'll just have to wait and see when I pull it off.

I'm still a semi-newb when it comes to internal engine work, so I have a few more questions: Now if the coolant is leaking across the gasket between the head and the block, will it be easy to spot once the head is removed?(Like some kind of build-up or sludge where the coolant was mixing with the oil?) If the head is slightly warped, it can be machined flat again, right? Can a machine shop also check to see if the head is cracked? What all is involved in that?

Any help is appreciated here guys!

-Chad

Click to expand...

Yep they can check for a crack. Magnifluxing works great so does dye penetrant. Basicall they coat the haed with dye or metal filings and apply UV light/another spray or magnet to find cracks. If the head gasket is leaking you will probably notice a defect easily. If the head is warped it can be machined flat, but make sure to check the block deck also becauise a flat head and a warped block will do you no good.

Pull the spark plugs. If one or more are clean, this will indicate which cylinder(s) thecoolant is leaking into.
Tom