Blown head gasket!

mts91xj

mts91xj

Active Member
Joined
May 16, 2012
Location
Fountain, NC (near greenville)
Went to drive my jeep to a meet and greet Saturday and got insane amounts of white smoke blowing from exhaust and oil literally flowing out the tail pipe! Pulled the valve cover Saturday night and to no ones surprise there was antifreeze pooled up on top of the head :( Got the head pulled Sunday, the gasket actually looked like it had no problems, but will be replaced anyways. Valves on 5 of the 6 cylinders were burnt / oily / wet. Will be cleaning the head good this week, scraping gaskets and so forth. Just looking to get advice on if there is anything else i should replace or check while i've got this thing apart already. (will be replacing rings as well, might as well do it while i've got the motor torn down this far.)

The good news is there is no knocking or ticking going on, so i'm fairly certain the bottom end is holding up just fine, no gouges / scratches in the cylinder walls, other than carbon / oil buildup the valves look good.
 
mts91xj said:
Went to drive my jeep to a meet and greet Saturday and got insane amounts of white smoke blowing from exhaust and oil literally flowing out the tail pipe! Pulled the valve cover Saturday night and to no ones surprise there was antifreeze pooled up on top of the head :( Got the head pulled Sunday, the gasket actually looked like it had no problems, but will be replaced anyways. Valves on 5 of the 6 cylinders were burnt / oily / wet. Will be cleaning the head good this week, scraping gaskets and so forth. Just looking to get advice on if there is anything else i should replace or check while i've got this thing apart already. (will be replacing rings as well, might as well do it while i've got the motor torn down this far.)

The good news is there is no knocking or ticking going on, so i'm fairly certain the bottom end is holding up just fine, no gouges / scratches in the cylinder walls, other than carbon / oil buildup the valves look good.
Click to expand...

IF the gasket showed no bad places, it's probably a good bet that the head is cracked. Only way to know for sure is to take it to a automotive machine shop and have it magnafluxed. This will show up any cracks in the head. What you saw pouring out the tail pipe is most likely where the steam(white smoke) is more or less cleaning the soot out of your exhaust system.

Now, talking about replacing rings, that's a whole different story. You can do the head work with the engine still in the engine bay. I have saw people do it, but replacing the rings while in the engine bay isn't recommended. If it is using oil and or smoking, the block needs to come out. Replacing just the rings is a very short term patch at the most. The rings are actually harder than the cylinder walls, so you probably have worn walls more so than worn rings. If this is the case it will need to be bored, honed, and new pistons and oil seals, rings. At the same time the crank should also be mic'ed to check for wear. There again, if you just go back with standard bearings, it is mostly just a patch. a goo indicator when looking at the bearings, is the wear on them.

Hope this helps
 
Stroked 4.0 (done by previous owner) appx 25k miles on the build.

Block - 92 4.0 Bored 0.060 over with 258 crank to make it 4.7
Head - 91 4.0 (he said he had it magnafluxed before he did the build)
Intake - 01 Grand Chrokee


I did overheat bad this summer in URE, but after changing spark plugs i have been driving it with no issues since then. Haven't had coolant loss problems. Oil has smelled a little like gas the last 2 times i changed it, and its always extremely black after only 2500 miles or so. Is consuming oil pretty bad, usually adding 2 quarts between oil changes.
 
I don't doubt that he had it checked when he built it. But, that was 25K ago. So yeah still can be cracked, and ya can't really say it was because of his build.
Oil smelling like gas? well if the injectors are too large, that could be that issue. If they are bigger than stock, which is a possibility when he was building, trying to get more out of the build, power wise. Then it could be dumping too much into the cylinder, causing it to wash down the cylinder walls and allowing gas into the crank case, and allowing oil to slip by.
Might want to run the numbers on the injectors to see what they are from. It could also be that they are the right ones, but, allowing gas to seep out when it's not running. Easy to check that by checking the pressure while running, then pressure just after you shut it off, then again the next day before you crank it.
 
I'll check the numbers on them tonight since they are out of the jeep already. Found a reputable shop in Kinston that can do Magnaflux or Pressure test on the head for me. Which would be better? I'm thinking pressure testing. The head is painted, so i can see that causing problems with the magnaflux? It was only a little more expensive to have them pressure test it. They will also be cleaning it up and checking everything else on the head as well.
 
The area that needs to be checked, magnafluxed, is the cylinder area's and on top around the valves. But the later is doubtful that that is where the issue is. there are no oil galleys in the head, so the only place that needs checked is anywhere the coolant flows or near where the coolant flows. You can clean the head up yourself, most places charge to do that. Just wash it down with degrease, and then wire brush the heck out of it on the combustion chamber side. You can use a knotted wire brush on a grinder, won't hurt a thing. then blow it dry with an air hose. you may see the crack if it's bad enough. When you take it to the machine shop, have them check it for flatness too. If a shop, and many do, used a belt sander to dress the surface, it could be way out of flatness. I am thinking the tolerance for something like that should be less than .007 or less. you can check that yourself with too with a good straight edge and some feeler gauges. end to end, corner to corner, and see if you can slide the feeler gauges under the straight edge. If it's a machining issue, then it will most likely be out on the ends, high in the center, if it's a wear issue, then it will be low between the combustion chambers.
 
oh and pressure testing is usually just for aluminum heads, as magnafluxing won't work on them. BUt either can be presure tested
 
he said no difference in price if i clean or bring it to them as it is. I want to say he said 25 dollars for magnaflux and 50 something for the pressure test. I'll be taking it to them tomorow on my lunch break and update after i hear from them.
 
Didn't even get that far..... The valve guides were sleeved from a previous build, and are not up to spec. Going to be cheaper to get another one and get a valve job done and call it a day. Thanks for your help and advice btw.
 
bummer. New guides are not a bad thing if done right, and last as long or longer than factory. I have put them in every thing from bone stock to race engines. And usually it allows you to put in a better valve seal
 
I have a 4.0 head sitting on the shelf condition unknown, needs to be checked out at a machine shop. Typically mismachine from the factory between #4 and 5 cylinders. Also have a 4.0 coming out of a 2000 wrangler 100k, it rolled over not much body left, sorry more left than straight.

Chris 828-964-5972
 
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