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New Guy, Excessive Blow-by on 89' 4.0

H

Heap O' Jeep

NAXJA Forum User
Location
Abilene, KS
Hey everyone, first time Jeep (and 4x4 owner) here and I was needing some advice from the pro's :yelclap:

I just purchased my Jeep Cherokee Laredo a week ago and my fellow Jeep enthusiast (Garden Spyder) and I were looking it over and noticed excessive blow-by on the engine block cylinder side of the head. It is so bad that it is quickly ruining my air filter by soaking it in oil AND depositing a large amount of oil in the bottom of the airbox. With 220,000 miles I assume that the engine has just seen better days, but is there any way to remedy this or make it slightly better? I just did an oil change and I put in 4 quarts of Rotella 15W40 and a quart of Lucas Oil Stabalizer.

Garden Spyder and I were discussing the idea of re-routing the "plumbing" that leads into the air box into somewhere on the intake of the engine, that way I wouldn't ruin as many filters quite as quickly.

Any thoughts or suggestions?

Thanks
 
probably a result of worn piston rings.... maybe check compression to check....
not much you can do easily.... maybe route it thru an air/oil seperator you might find for an air compressor... if kansas doesnt have smog, route it down and let it drip... maybe clean the inside of the valve cover passageways, make sure nothings blocked w/ crud....

welcome to naxja, home of the search nazi's
 
I am pretty sure that your RENIX vintage has two basic lines from the valve cover. One goes into the intake manifold and one goes to the air cleaner. If you search, you can find where various filtered breather systems can easily be built with a separate oil tolerant filter. The line going from the air filter is supposed to take air from the filter area into the valve cover. The other line is supposed to provide a vacuum from the intake manifold to the valve cover. If that line gets clogged up, it can't provide enough vacuum, especially on a motor with a little more blowby. Try cleaning that line out to see if that improves the problem, while still retaining the original plumbing.
 
As Winterbeater says, the small line at the rear has a metered orifice in it (2.5mm). I use a smaller drill bit to clean it out, then TB cleaner to flush. Also, remove your valve cover and clean out the insides, especially around the baffles leading to the hoses. Sludge buildup there can restrict the flow of air as well.

You should also do a compression test. If the rings are leaky, you may have to resort to one of those rigged up "oil traps".
 
Yup, as others have said, that is a common symptom of a clogged PCV valve on 4.0's.
 
Ditto on the cleaning of the PVC system. Also sounds like your value cover gasket is blown out R+R as needed there.
Is the XJ built up for offing or any other form of competition? If so. She been subject to high RPM and/or stress loads, If you keep this type of use up. Expect the blowby to increases. If your going to keep the stress and RPM down the blowby MAY go away or decrees a lot. luck.
 
Actually, it is a CCV system, there is no PCV on the 89 Renix 4.0.
 
joe_peters said:
Actually, it is a CCV system, there is no PCV on the 89 Renix 4.0.
Click to expand...
Sorry, i put one on mine, i forgot stock they don't have them.
 
Definitely check compression, but may I recommend, an oil change. Along with that use some Engine restore and some MMO.. see if that helps at all.
 
winterbeater said:
OK, I give up what's a CCV? Controlled Crankcase Ventilation or what?
Click to expand...

CrankCase Ventilation using a fixed orifice versus Positive Crankcase Ventilation using a variable valve.
 
Thanks for all the help and links to prior threads. I will try to take everything into consideration and post up my results.

I think that I forgot to mention that I just changed the valve cover gasket a few days ago and I now have no leaks that I can see. Oil is changed with 15W-40 Rotella and Lucas oil stabalizer. The Jeep will be used for minor off-roading and as a street-driven vehicle.
 
My 87 had alot of blow-by when I first bought it. The steps I did to stop the blow-by.

1) Flush the engine crank case
2) Seafoam the engine ,do all three steps on the can.
3)Check the CCV system for any clogged lines, Gotta make sure everything is flowing and breathing properly.
4) I bought the complete new CCV system and replaced it . 90.00 from dealer
5) I changed my engine oil every 3,000 miles with high mileage oil with one qt. of Marvel Mystery oil.

My blow-by was so bad at first , I installed a oil catch bottle between the engine and air filter.
After going through the steps my blow-by went to almost nothing.

Good Luck
Nick
 
do any/all of the above mentioned....if you still have excessive blowby you can then try swapping a later model stamped steel valve cover on. There are a couple of differences between it and the older style covers that keep oil in the engine. The vaccuum line at the rear is larger for one, but the big difference is inside the cover....the older style uses a set of "towers" that sit closer to the top of the head (closer to the oil), but the new style uses a baffle plate that runs the length of the cover at the top. You'll need a different gasket, and will have to reroute both the vac line and the fresh air line at the front, but it'll help alot. I put one on my 87 4.0 about a month ago, and I have zero oil in my airbox.

Jeff

edit: here's a link to my writeup over on ComancheClub, with pics of what I'm talking about

http://www.comancheclub.com/forums/viewtopic.php?f=2&t=12871
 
Last edited:
There are alternatives.

Using Restore to get the rings sealing up again probably won't hurt. The basic idea in protecting the filter is to capture or divert the drain back of oil from reaching the filter.

1) Use a Cone filter with cold air baffling and reroute the hose to the intake tube.
2) Build a blowby trap and install it in the line.
3) Use an old fashioned Chevy cover breather and let the oil drain down the valve cover to drip on the ground.

I'm trying #3 and it works really well at keeping the filter clean!
 
Garden Spyder and I gave it a good look-over, and realized that the vacuum line to the intake manifold was completely plugged! We were getting no vacuum at all, so we cleaned out the line and then got plenty of vacuum after the cleaning. I also replaced the oil-soaked air filter with a new one, and that one has barely any oil contamination after driving it for days.

I also did the Seafoam treatment to the intake and the gas tank. I will be doing it in the oil too when the next oil change comes up.

I am going to try the Restore stuff on the next oil change also to try and relieve some of the blow-by.
 
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