Blown head gasket on 258 I6? -
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post #1 of 8 Old 01-05-2008, 11:52 AM Thread Starter
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Blown head gasket on 258 I6?

Hey guys, I was headed out to go camping last weekend with the CJ and a few friends and it ended up overheating. It turns out the hose that goes from the thermostat to the intake manifold had cracked and was spewing coolant all over until we finally realized it and pulled over. Unfortunately it had probably been spewing out for a while until we realized it.

I had it towed home on a flatbed and it didn't sound all that great when I put it up. I didn't have the time to look at it because I was headed out the next day to El Paso for the Sun Bowl, and when I returned I finally was able to run off the girlfriend for a while and take a look at the damage yesterday. It sounded down on a cylinder when I first cranked it (I replaced the hose and filled the coolant back up), but it wasn't leaking anything out of the head or anywhere else and it wasn't shooting water out the exhaust, so I took it around the block a few times and was pretty hard on it to see if anything would happen.

It seemed to be OK, so today I changed the oil and didn't find any water in it. The oil cap has some of that milky substance meaning that there's oil in the valvetrain, and the PCV had the same fluid on it as well. I checked and changed the plugs, and a few of them looked like they had seen water, and one of them had a good bit of oil on it.

I'm scared to drive it too far, yet I can't decide whether or not I should bite the bullet and pull the head to replace the head gasket. It runs smooth as ever now, and it still doesn't leak water out of the head gasket that I can tell, and there is only a little condensation buildup on the exhaust that disappears after it warms up. The thing that scares me is that the plugs looked like they had seen coolant, and the one had oil on it.

What do you guys think? Pull the head or not? If I do end up pulling the head, I'm going to swap to a 4.0L HO head with an aftermarket header with straight back exhaust and a cherry bomb and Offenhauser or Clifford intake manifold (I'll keep my Weber 34/34 for now). I'd really hate to spend the money and don't really have the time to pull the head, but if you guys think it's necessary then I guess that makes up my mind. Thanks in advance!

1986 Jeep CJ7 4.2L I6 T176 (restoration in progress)
1961 Willys 4x4 Wagon L-226 I6 T90 (restoration also in progress)
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post #2 of 8 Old 01-05-2008, 12:07 PM
Mike Romain
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Lookin' for a good excuse eh?

I would suspect a bad wire on the oily cylinder but a fast compression test will tell a lot. The parts stores sell compression testers cheap.

After the drive I would inspect the plugs again. If you have any clean like new, then you can figure the head gasket is blown to the water jacket there, but it doesn't sound like it.

One other quick test is to open the rad cap and watch the coolant when the engine warms up enough for the t-stat to open. Stand back because it can be an explosion if the rad is seeing engine compression. If if is all foamy like dish soap you have troubles. I put a photo on the first page of tiny bubbles here:

86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
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post #3 of 8 Old 01-05-2008, 02:24 PM Thread Starter
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That is a pretty good excuse to give my 258 I6 a little more ponies, but unfortunately I'm about to invest in upgrading my axles instead, so I'd rather not have to spend the money on the motor.

Well, that was one thing I forgot to pick up when I ran to Auto Zone for my oil in my other car. AZ actually has them where you can rent them for a $20 deposit or something. I'll probably do that tomorrow to see what comes of it. I didn't think of the radiator trick either, thanks for the info. I'll have to give that a try as well.

1986 Jeep CJ7 4.2L I6 T176 (restoration in progress)
1961 Willys 4x4 Wagon L-226 I6 T90 (restoration also in progress)
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post #4 of 8 Old 01-05-2008, 03:33 PM
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Man going on just what you posted, I'd think your head gasket is probably ok. When mine overheated ( I ran a stick through the radiator at night) it sprayed water everywhere under the hood. I actually had to clean out the distributor cap to get it to run right from all the moisture. I'd bet you sucked a little water through the air cleaner while running and that's the moisture around the plugs. The milky oil on the pcv and the filler cap, well you live in a warm climate where it's colder then normal lately, I'd bet that's condensate that didn't get a chance to cook out after you over heated. My boat motor will show milky oil on the filler cap but never in the crank case, but only in the cold water monthes here in Havasu. I hope it all works out, good luck.
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post #5 of 8 Old 01-06-2008, 06:56 AM
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Just change the oil, fix the leak fill it up with coolant and drive it! Actually, you probably need to change all of the hoses, the belts and do a "cap,rotor,wires & plugs" while you are in the tinkering mood!

Another thing to change would be the Thermostat, if you got it that hot it may cause the T-stat to stick later.

Also, be SURE to replace the Air Filter! I would bet that it got soaked with AntiFreeze and will never flow correctly even when it drys out.

I love this post... Just try that little emergency with one of those lovely new Wranglers running the MiniVan Aluminum Engine!

Can you say, POOOF!!! One flash wonder up in smoke!
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post #6 of 8 Old 01-06-2008, 06:10 PM Thread Starter
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Hehe, yes I love my cast iron 258 I6...

1986 Jeep CJ7 4.2L I6 T176 (restoration in progress)
1961 Willys 4x4 Wagon L-226 I6 T90 (restoration also in progress)
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post #7 of 8 Old 01-07-2008, 12:37 PM
UPJ Wheeler
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MAN!!!! Im having the EXACT same symptoms right now with my 258 (rebuilt with 11k on it, carter carb), I also have a 4.0 head thats rebuilt sitting on my work bench.

One thing thats different is my exhaust temps are high enough to cherry the manifold (cyl 4, 5, 6).

Im not sure that mine is the head gasket though, and I dont want to put a brand new head onto a motor that will continue to have exhaust temp issues if the head gasket isnt the problem.

'79 CJ7, rebuilt 258, HEI, T5 World Class, D300 Low max 4:1, Flat Belly, Narrowed D44 w/ true trac & diff gaurd, Widetrack AMC20 w/ superior shafts, Detroit locker & crane diff cover, 4" skyjacker lift, 2" BL, TJ flares, 35" tires, York OBA, YJ tub conversion, 6 pt. cage, F250 front shock towers

4.0 Head and TBI on the way
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post #8 of 8 Old 01-07-2008, 01:16 PM
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I drove a 258 for over 5k miles with a blown head gasket.
When I figured it out- I pulled it, wiped the gunk out of the rearward cylinder, put on a new gasket and drove it for another 20k with no trouble. No headwork, no checking the mating surfaces just good old backyard mechanic skills. I was hoping it would not run. I could not kill that engine. Sold it when I swapped in a 304 and it might still be running.
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