Blow by?

hey guys, I did a search on this, but not sure if i got what i needed. I have an 89 with 230K on it. I just bought it and began tearing into it. The air filter is soaked with oil. I am assuming its blow by, but how bad is this and can it be fixed by cleaning all the tubes and or replacing them, and cleaning the valve cover? I am hoping its not something more invovled....

I had pretty severe blow-by on my '88 w/ about 200K. I replaced all of the CCV lines, cleaned the valve cover and made sure to clean out the air box and duct work. Problem solved.....

Make sure you also clean out (or replace) the rubber grommets in the vavle cover. I don't remember if you get new ones in the hose kits or not.

Good luck. It's not very hard to do. My '88 ran much nicer and sounded a whole lot better after the fix.

kool, sounds like a not so hard fix. Thanks for the info. ....
off to the dealer...

Where would one get the front hose on the valve cover, the one to the airbox? On a Renix 4.0L?

Your problem isn't blowby, it's the CCV system working in reverse. The thin tube from the back of the valve cover to the front of the intake manifold is likely clogged. My 212K MJ was completely clogged. Brake cleaner finally penetrated the carbon buildup and cleaned it all out. Once that's clear, Take the airbox end off the large hose coming from the front of the valve cover. This hose should be sucking air from the airbox into the valve cover. If it is the CCV system is working correctly and you shouldn't have any more air in the airbox.

http://www.off-road.com/jeep/cherokee/xjtech/engine/40ltr/blowby.htm

I printed it and took it to the dealer; the Parts guy asked if he could keep that to show the 'techs' working in the service department...contrary to what some folks around here think, many of those people are clueless and don't have the first friggin' clue how to fix a common problem with the 4.0L

If you find a lot of crud built up in the drain holes and such (all over) in/on the head, is there a product that's made to spray or pour on that dissolves this on while assembled? If there is, would it also work on the lower engine if you poured it in the pan (for clearing the pump screen, etc)?

Maybe something that disslves it on contact so you could get it clean in the hard to get at places?

it isnt necessary blow by. it sounds like it could be a plugged pcv system. over thim the grommet at the rear of the valve cover gets stopped up. you can get this grommet from the dealer, and it comes with a new hose. also when replacing the hose, make sure the vacuum fitting in the intake isnt clogged also. then replaced the 2 part ccv harness. thoroughly clean the throttle body, andset the base idle as i have described in a previous post. that should help with performance and idle quality.

What you are having is probably not from blow by, blow by exists when you have high oil consumption from from the piston rings not sealing properly, "The oil blows by the pistons ", I would bet you have a crankcase ventilation issue. I would start there just as stated above!

The rear CCV hose on my '88 MJ 4.0L was completely clogged, pushing a ton of oil into the airbox. I just bought it so the previous owners were likely oblivious to the cause. Brake cleaner finally cleaned the gunk from the hose, and now the CCV system is working correctly and the hose from the front of the valve cover is know sucking air from the airbox.

Re: Blow by? valve cover & ccv lines

I have a XJ 93 country, it was burning about 1.5+ quart of oil every 5000kms and pulling oil in the filter. I went to the junk yard, pulled the valve cover, gasket, both vacuum lines, and the brass valve that screws into the engine off a 2000.. it is a direct bolt on! only cost me $50 (hundreds new from the dealer) The diameter of the tubes and the brass valve are over double the size creating much higher pressure and the cover has a splash guard in it. not being a mechanic, I took me only about 20 minutes, and I noticed my oil pressure almost double after I did the swap (on the 1-5 dash gauge it used to sit about 2 now it sits at about 3.5) I just changed the oil and air filter, but I've only gone about 2000kms on it so far but no oil on the filter yet and oil level is still good. I'll keep ya posted after a few 1000 more K's. good luck with yours!

Quote:
I have a XJ 93 country, it was burning about 1.5+ quart of oil every 5000kms and pulling oil in the filter. I went to the junk yard, pulled the valve cover, gasket, both vacuum lines, and the brass valve that screws into the engine off a 2000.. it is a direct bolt on! only cost me $50 (hundreds new from the dealer) The diameter of the tubes and the brass valve are over double the size creating much higher pressure and the cover has a splash guard in it. not being a mechanic, I took me only about 20 minutes, and I noticed my oil pressure almost double after I did the swap (on the 1-5 dash gauge it used to sit about 2 now it sits at about 3.5) I just changed the oil and air filter, but I've only gone about 2000kms on it so far but no oil on the filter yet and oil level is still good. I'll keep ya posted after a few 1000 more K's. good luck with yours!

do you know what year they started putting the bigger tubes and the splash guard in?

I had this occur out of the blue on the way to moab. Found the elbow on the hose from the intake to the back of the valve cover broken along with a bad grommet going into the back of the valve cover loose fittings going into the TB. Replaced all and it's not blowing a quart of oil per tankfull out through the aircleaner anymore.

I think '99 was the first year for the bigger tube. Check out the MAD-XJ website for an article. Technically blow-by is from the rings, but this problem has been labeled 'blow-by' in various articles. Get a good seal on the valve cover. If you use the '99+ CCV tube on a Renix motor (87-90), then you will have to cut it in two and add some fuel line or vacum tubing to add length. I did this on my '88 and it took care of the oil in the air filter. I also used a '95 valve cover. The 90 degree elbows are suppose to control the oil mist a bit better.
Tom