I recently took my jeep to a mechanic because it was showing all the signed of a cracked head after doing a 700+ mile trip (coolant loss, fluids in the oil, occasional power loss, oil pressure had dropped 8psi over 2 months). its been two weeks that they have had it, he's been running it for hours, has been driving it on errands or to and from home and cannot replicate the symptoms of coolant loss or coolant in the oil. He did say the oil pressure idles at 12psi, but he can't tell me definitively that its cracked...

He wants to send it out to be cleaned and magna fluxed but I feel like thats going to be a huge waste of money, because I will still need to replace the head afterwards if (and its a highly likely 'if') that its cracked. At this point I'm leaning towards just replacing the entire engine, he has one with a clearwater head lying around, that hopefully if he can give me a good price on ill probably just go with.

What else can show signs of a cracked head but not be a cracked head? Should I have it sent off or just replace the head outright? Or the whole engine?

I've attached a photo of the oil drained into a plastic water bottle after the first 350 miles of the mentioned trip

 

Here's some info:
https://www.cherokeeforum.com/how-to...rmation-398176

You could also send off an oil sample to be analyzed.

 

X2. I'm betting you have the infamous 331 cracked head. The declining oil pressure is a bad sign that it's been eating the bearings.

 

I do have the 0331, I mean, I'm convinced the head is cracked, just surprised they can't confirm it! And at 12psi, replacing the whole engine seems like the most effective and long term solution... how much does it run to have a magnaflux job done? It just seems like a pointless endeavor at this point, but what do I know! thats why I pose it to you good folk, haha

 

12psi at idle isn't that low. Factory spec is 13psi. Your mechanic can verify it with a mechanical gauge.
These cracks can be very subtle and the only way to know for sure is to have the oil analyzed.

https://www.blackstone-labs.com/

 

Um, did anyone put a simple radiator pressure gauge on the radiator and pump it up? Most simple sure fire test there is.

 

And look through the oil cap at where it usually cracks?

 

That's where my head cracked , just take a flashlight and look though the oil cap opening in the valve cover at the head you should see a very small amount of coolant coming though the head but the coolant system needs to have pressure in it so the coolant will come out of the crack .

 

He cant seem to find a crack, and running it for weeks cant seems to get symptoms either, he says. Might be a hairline, and I dont know about the radiator pressure though nothing seemed glaringly wrong with the car beforehand except oil pressure.

I dont have the jeep, it's at his shop now. Without a garage, a head swap is more than I want to tackle curbside.

What else can mimic a cracked head symptoms bit not he a crack?

 

"Might be a hairline....."

https://www.blackstone-labs.com/

Have your mechanic test for exhaust gases in the coolant.

 

Easy, I've had two non-jeep vehicles which the head gasket corroded, due to age, at the metal ring around the cylinders. I've also had head gaskets delaminate and create a small passage between the coolant and oil passages. The coolant is under pressure and over time can do that. I'd have pulled the head a long time ago. Usually you can see those problems when ya remove the head gasket. If need be, get a new (replacement) head.

Are any of the spark plug insulators different color? Do you know what cylinder (if any) are affected?

 

Also, this is going to sound stupid but, you might consider running some of that "Head Gasket Repair" in-a-can stuff in your coolant and see how it goes. I know it sounds preposterous, but when I was really young and stupid I bought a Mustang 4-banger for $25 that had a cracked or warped head. I replaced the head gasket which made no difference. I poured in a can of the head gasket repair and followed the instructions to a 'T'. It clogged the leak. We beat the heck out of that car thinking it would leak again soon. It didn't. I drove that car all summer till I could afford something better, and gave it to my brother -- who proceeded to drive it for 2 years ...took it on a interstate vacations, all over. It wouldn't die! He eventually traded it for a newer vehicle for $500 or whatever they gave him. In that time he had to re-do the head gasket in-a-can 2 more times.

Not something I would advocate for most people, but it's an option if funds are 'no-to-low' .

Good luck

 

Your right it could be a head gasket issue. In my opinion it needs to be found out if there's an issue with the head or gasket before the head is pulled. That's why I've suggested the tests. The one for exhaust gases in the coolant can get results right away whereas the oil analysis will take time. This couldn't hurt either:
"Um, did anyone put a simple radiator pressure gauge on the radiator and pump it up? Most simple sure fire test there is."

 

Well if the head gasket is the issue, you can have combustion gasses leaking into the coolant just like you would with a cracked head. I usually just put my nose down into the radiator cap and give a good sniff. Harder to do on these Jeeps b/c of the overflow tank. They make test strips for that job too, I believe. Also sniff the exhaust for sweetness (antifreeze).

You have to weigh the time and money you're spending to have the mechanic test everything or to just remove the head and take into a machine shop for pressure testing. They're actually not that hard to remove, taking off the intake/exhaust is the hardest part if ya haven't done it before. But if ya remove the headgasket, give it a VERY careful look-over. A sloppy mechanic may not take the time to spot a small leak, if there is one. You can read a headgasket and learn a lot.

 

Can I add my 2 cents? Having had a cracked 0331 head already, just the look at the oil in that bottle is enough for me to say it's cracked. Even if it's just a blown head gasket, the history of that head casting is enough for me to take the head off and replace it, before it totally destroys the engine. The sooner you replace it, the longer the bearings will last now that they are compromised.

My opinion on the replacement engine? It's an unknown factor because you don't have any history on it, even though he says it's good. I got suckered into an engine swap from a friend who said he had a CSB that was running good when he pulled it from his Impala and it was in worse shape than the one I had!

Replacing the head is the cheapest way to go. A new head with valves will cost you in the $500 range and even if you need to replace the engine in the future, you'll already have a good proven head for it. Just my opinion.