BentGear Posted April 21, 2021 Share Posted April 21, 2021 I'm new to the community, just bought my MJ a few weeks ago. It's leaking oil like crazy, the guy who sold it to me said it just needed a valve cover gasket, but looks like it needs more, one of the cylinders is blowing by. I'm considering a full rebuild, even though I have never done it before. I know a few people who can probably help if I get stuck. Any thoughts on what is the best rebuild kit? I don't want to cheap out, I want to build this thing into a real reliable daily driver for my son, so if swapping it out is a better idea I would consider it. It is posted on the registry https://comancheclub.com/topic/65926-1jtml63p7jt248460/ Link to comment Share on other sites More sharing options...
jdog Posted April 21, 2021 Share Posted April 21, 2021 Have you done a compression check yet? No sense in rebuilding a good motor if it's just simple things wrong. Link to comment Share on other sites More sharing options...
BentGear Posted April 21, 2021 Author Share Posted April 21, 2021 12 minutes ago, jdog said: Have you done a compression check yet? No sense in rebuilding a good motor if it's just simple things wrong. Yes, I had a shop go through it and they said one of the cylinders is blowing into the crankcase. I drove it 3 hours from where I bought it with no problems, I think it runs well when warmed up. Link to comment Share on other sites More sharing options...
jdog Posted April 21, 2021 Share Posted April 21, 2021 Numbers? Also if they say it has blowby did they do a leak down test to say which cylinder is causing this? How did the come to the conclusion that it has blow by? Have you used this shop before, not saying they aren't good just trying to get some facts. But if your set on their diag. It all depends on the plans of the truck and time frame Link to comment Share on other sites More sharing options...
Pete M Posted April 21, 2021 Share Posted April 21, 2021 the ol' 4.0s are known for blowing some pressure into the crankcase. it's super common and that alone isn't enough to write it off. unless one particular cylinder is mega worse than the others. but without the compression/leakdown numbers, it's impossible for us to call it from our end of the internet. I'd hate for you to rebuild the whole thing when all you needed was to pull the valve cover, do the blowby mods to it and reseal it up nice and tight. Link to comment Share on other sites More sharing options...
75sv1 Posted April 22, 2021 Share Posted April 22, 2021 As others have said, need to do compression check. Also, where is the oil going to? Is it going to the air filter box? There are other seals that might need replaced. Front crankshaft seal, rear crankshaft seal and the oil filter seal(s). Also, what year? Really not much difference, but the HO valve covers are a bit better. I prefer a Valve Cover from a 93-98 Grand Cherokee. It have the CCV setup from the latter steel valve covers. Also, look at Cruiser tips to modify the internal valve cover baffles. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 22, 2021 Share Posted April 22, 2021 Could be as simple as doing this Tip and installing a Felpro valve cover gasket. http://cruiser54.com/?p=131 Link to comment Share on other sites More sharing options...
75sv1 Posted April 22, 2021 Share Posted April 22, 2021 Also, I use the rubber or silicon FelPro gasket. The cork ones lose compression. Or use RTV and get a good seal. Link to comment Share on other sites More sharing options...
BentGear Posted April 22, 2021 Author Share Posted April 22, 2021 Thanks for all the help so far, here is what I know from their notes: "Air filter is completely saturated in oil as a result of engine blow-by. There is cylinder pressure leaking past the piston rings into the crankcase. The valve cover gasket is leaking badly but replacing the gasket would not keep blow-by from happening. Oil pan is also covered in oil and pan gasket is leaking as well. Based on engine wear, mileage, and what can be seen at this time, the engine should be rebuilt or replaced." I do not know the shop well, as it was pre-purchase inspection. The air filter does have oil on it. Should I start by replacing the valve cover gasket and air filter and see if it continues to get covered in oil? I do not have the compression numbers from the shop that looked at it. Link to comment Share on other sites More sharing options...
scaleless Posted April 22, 2021 Share Posted April 22, 2021 Frankly I would clean off the block so you can see exactly where the oil is coming from, replace the air filter and the valve cover gasket since they're cheap and easy, and just monitor the engine for a while. Do a compression test if you have the ability to. Oil on the air filter isn't 100% indicative of excessive blowby - it will naturally find its way to the airbox because of the PCV system and if they never change the filter it will start to get soiled. I've driven vehicles with absolutely ludicrous blowby for long times - just make sure the oil is topped off and you'll be more-or-less ok. Once you understand exactly what's going on with the engine, you can get an idea if it needs a rebuild or not. You say you drove it 3 hours with no problems, so it's not nearly as bad as it could be. My Corvette's old engine blew a quart and a half an hour out of the seals and drove just fine. Link to comment Share on other sites More sharing options...
Pete M Posted April 22, 2021 Share Posted April 22, 2021 the blowby in my 88 is so bad I installed a catch jug before the filter. still drove it out to Moab and back. near all 4.0s will have oil in the filter. Cruiser's tips cover how to reduce it substantially. Link to comment Share on other sites More sharing options...
omega_rugal Posted April 23, 2021 Share Posted April 23, 2021 Quote the blowby in my 88 is so bad I installed a catch jug before the filter. this, an oil catch can solves the oil in air problem, it doesnt have to be fancy either... Link to comment Share on other sites More sharing options...
BentGear Posted April 23, 2021 Author Share Posted April 23, 2021 Thanks all, I'll give that a try. Link to comment Share on other sites More sharing options...
scaleless Posted April 23, 2021 Share Posted April 23, 2021 11 minutes ago, Pete M said: Cruiser's tips cover how to reduce it substantially. Specifically, #25: Valve Cover Mod http://cruiser54.com/?p=131 Link to comment Share on other sites More sharing options...
cruiser54 Posted April 23, 2021 Share Posted April 23, 2021 do this^^ and use a Felpro valve cover gasket. Likely fix it all up. Link to comment Share on other sites More sharing options...
jdog Posted April 23, 2021 Share Posted April 23, 2021 1 hour ago, BentGear said: Thanks for all the help so far, here is what I know from their notes: "Air filter is completely saturated in oil as a result of engine blow-by. There is cylinder pressure leaking past the piston rings into the crankcase. The valve cover gasket is leaking badly but replacing the gasket would not keep blow-by from happening. Oil pan is also covered in oil and pan gasket is leaking as well. Based on engine wear, mileage, and what can be seen at this time, the engine should be rebuilt or replaced." I do not know the shop well, as it was pre-purchase inspection. The air filter does have oil on it. Should I start by replacing the valve cover gasket and air filter and see if it continues to get covered in oil? I do not have the compression numbers from the shop that looked at it. Yep, sounds like the shop didn't want to deal with it, or care to even make an effort to figure out where the leak was and how healthy the engine is. Do cruisers valve cover mod, change the gasket and wash the engine Link to comment Share on other sites More sharing options...
75sv1 Posted April 23, 2021 Share Posted April 23, 2021 In my experience, a leaking valve cover gasket causes an air pressure imbalance. So, the Intake air suction sucks oil into the air filter. I did struggle with this on my '88 Comanche. I think the RENIX system is the worse. I tried several cork gaskets. They would last maybe a month. I did get it cures, but then the master clutch cylinder went out. So, follow the Cruiser VC upgrade. Use a FelPro rubber gasket. Also, you could just put one of those Hot Rod VC filters on. That way, the Airbox is not sucking oil out. Link to comment Share on other sites More sharing options...
BentGear Posted April 27, 2021 Author Share Posted April 27, 2021 Update: I put a FelPro gasket on, no oil leak now. I did the Cruiser 54 mod. I had to clean a lot of carbon out of the valve cover. Now there is a loud vacuum leak, at least that is what it sounds like and I cannot pin point it. It is not the valve cover connections. Sounds like its at the exhaust manifold. I see a little smoke coming from that area when I startup, but it goes away after 30 sec of idling. The truck idles rougher now, and there is more white smoke in the exhaust than previously. Do you think this is a vacuum leak or an exhaust issue? Could the sound just be the vacuum lines pulling though the modified tubes in the valve cover? Not sure where to go look next. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 27, 2021 Share Posted April 27, 2021 Make sure all your intake manifold bolts are snug. Looking for vacuum leaks? Spray carb cleaner on suspected leaks. You'll know when you find one. Link to comment Share on other sites More sharing options...
BentGear Posted April 28, 2021 Author Share Posted April 28, 2021 I think I found the culprit, but I don't know what it is. See the photo below. This looks like an emissions connection, it was disconnected. I put it back in and the engine runs much better now. I can still detect a little leak coming from the rubber grommet probably because it is so old. I pushed the connection in as far as it would go, but I didnt want to push too hard and break the old rubber grommet. Can anyone tell me what this is so I can order a new one? Should their be another hose connected to the top hole? The top hole does not seem to have air flow, in or out of it. Link to comment Share on other sites More sharing options...
BizarroStormy Posted April 28, 2021 Share Posted April 28, 2021 That goes to your MAP sensor, very important for your computer to control your engine. Look at Cruiser's tip #31 to replace this weak connection with an improved one. http://cruiser54.com/?p=280 Link to comment Share on other sites More sharing options...
rokinn Posted April 28, 2021 Share Posted April 28, 2021 2 hours ago, BentGear said: Should their be another hose connected to the top hole? No! It just holds that grommet to the throttle body. Link to comment Share on other sites More sharing options...
JMO413 Posted April 28, 2021 Share Posted April 28, 2021 4 hours ago, BizarroStormy said: That goes to your MAP sensor, very important for your computer to control your engine. Look at Cruiser's tip #31 to replace this weak connection with an improved one. http://cruiser54.com/?p=280 Link to comment Share on other sites More sharing options...
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