Hey all new to forum.
Ive read alot on here and thanks to those who contribute and share knowledge. The information is VERY helpful. Ive had a few jeeps over the years. Just sold our built 01 wrangler sahara with 35s that my wife drove daily for 3 years for something a little more practical. damn sho got a alot of attention in that thing! Lol
So i picked up this 99 cherokee xj 4.0L in august with 192k. Ran good no issues other than maintenance an a driver floorpan. I flushed coolant multiple times and changed oil /transfluid etc. I noticed low oil pressure at hot idle and did the usual cleaning of oil sender and noticed it was newer. After couple months of driving and a random check engine light for rear o2 sensor issue i noticed it started eating coolant. No leaks but it was emptying the overflow every week. I kept it topped off but knew the motor needed a rebuild soon since it had 192k miles and I didnt want to keep adding coolant every week since winter was coming and that gets expensive. The oil level was always good and appeared clean so I wasnt to concerned yet. I figured it was burning some coolant and causing o2 issue and since it ran fine i figured id wait.
One day i checked oil and it was overfull. i looked inside valve cover and it looked like butterscotch caramel in there so i knew i wouldnt be driving it till a rebuild since i didnt want to risk losing a bearing and cant add just water in winter etc.
So i pulled engine and sent to reputable machine shop. They pulled it apart and found no evidence of any problem besides the contaminated oil itself. They fluxed the head (0630) and found it is good. They also said that the head gasket had been done recently which i suspected and looked good and was properly installed. So the head and head gasket were both good. They are going to bore it .030 over and crank .010. new pistons bearings etc etc

So where is the coolant getting into the motor?

I gave them my intake manifold to clean since it was full of oil buildup thanks to the ccv system. After cleaning the intake they noticed what appeared to be a crack under the throttle body at the bottom of the plenum.

They called another guy who is , as they said, "a jeep guy" and he told them hes seen this issue before with the intakes cracking. Apparently a cracked intake will allow condensation/ moisture into the engine through the CCV system? That still doesnt explain the coolant loss to me.
Have any of you ever seen or heard of this issue? I will post a pic. My exhaust manifold was also cracked in at least 2 places so thats getting replaced too with an APN.
Just wondering if this is something thats even possible. A cracked intake manifold causing the engine to fill up with coolant. Doesnt sound right to me since theres no coolant in the intake. However i know the CCV system and its dumping oil into the intake isnt good. Ill do a catch can for that.

The engine is getting a full rebuild at this time since it needed it anyway I and will be putting a different used intake on it just to be safe. it will also get new water pump.
Thoughts about intake crack? It looked like a casting mark to me at first but i can see how it could be a crack. Its not all the way thru visibly.
Thanks for any input




Travis

 

The mark in the intake manifold is a red herring. It has nothing to do with coolant in your oil. If it's actually a crack, it would cause a vacuum leak.

If the head is good and you don't have a crack in the block, you had a leak between the head and the block. If the head gasket was recently replaced, I would be wondering whether the head surface wasn't true and wasn't letting the gasket do its job of sealing it up. Additionally, one of the head bolts passes through a water jacket and needs thread sealant on it. Somebody probably just did a half-*** job on the gasket replacement.

I assume you had a machine shop check the mating surfaces to make sure they're flat before starting the rebuild? As long as everything has been checked for cracks and flatness, I would think the rebuild would go smoothly.

ETA: Are you sure that manifold is cracked and not just a casting flaw? Does it show on the bottom of the manifold as well? That's a rather odd place for it to crack.

 

thanks for reply,
yes the shop is going to mill the deck and head to be sure. Good to know about the head bolt in water passages. Ill make sure they are aware of that too. The mileage was horrible but i assumed that was because of cracked exhaust manifold and coolant being burned throwing off the mixture etc.
I just spoke to the shop and they said upon teardown some of the headbolts appeared to have sealant on them so hopefully it turns out to be a flatness issue with the mating surfaces even though the head gasket looked good visually

 

Since we're on the subject, does anyone have the flatness specs for the head and block? I'm doing the same thing right now and want to check it before I put things back together.

Travis, I hope you don't mind me hijacking your thread this time.


EDIT: Found part of it. .002 for the head.

 

Copied this from my 97 fSM.

4.0L Block and cylinder head flatness
0.03mm per 25mm (0.001 inch per 1 inch)
0.05mm per 152mm (0.002 inch per 6 inch)

Flatness max
0.20mm max for total length (0.008 inch max for total length)

 

Perfect! Thank you!