Exsessive Blow-By Fix?

I have an 1987 cherokee with a 4.0 it has 266,000 on it and i was wondering what was the best fix for exsessive blow by in the front valve cover tube.

266,000 miles and going....

Maybe time for a rebuild.

Nick

naw, i had a 89xj that went to 298,000 no problem. I think im going to replace the pcv and all air hose's, maybe eliminate a few and go the snorkel route.

It's all about ring seal. 4.0's with more than 150K seem to suffer a lot more, especially under load. Cleaning up the tubing only fixes them, not the problem.

1) Rebuild the motor - and get a newer cylinder wall to piston ring working seal.

2) Pop in a later model motor - with the better head, intake, etc, and enjoy another 30 hp over the old models.

3) Use snake oil. Restore is one brand of cylinder wall sealer that claims to increase compression - which is exactly what is being lost. I tried a can in a 4 cylinder that was down to 20 pounds on two cylinders. It actually runs smooth now. The makers claim it needs to be added each oil change, IIRC. It would be worth trying compared to the $650 to $1800 cost of conventional repair. A motor with 250k won't cost much getting an additive every 3-5k for the remaining life it has.

4) Eco unfriendly - pop on a Chevy valve cover breather and watch the oil drain down the engine. At least the air filter stays clean.

5)Fab a oil catch can in the breather hose and dump it as needed. Better than #4.

I'm not disagreeing with TiRod, but you are on the way with the first step by making sure that the vacuum side of the breather system is clear. If you search some, you can also find threads where people have rigged up systems to reduce oil in the air filter.

Have you done a comp check yet? if is not above 120-150 I would look at rebuilding it,i have read alot about folks putting in traps and devices to keep it out of there air filter and if that is all you want to do then thats ok,but that does not stop the blow by. You have to rebuild it to stop it.

dude i just had this problem time for rebuild sad but true.

winterbeater said:

I'm not disagreeing with TiRod, but you are on the way with the first step by making sure that the vacuum side of the breather system is clear. If you search some, you can also find threads where people have rigged up systems to reduce oil in the air filter.

Click to expand...

X2.

All I can say is wow, all the "go rebuild it responses, with no data, and no one even asked what he means by blow by?

Truth is 4.0's are notorious for imitating blow by, throwing oil into the air filter when the only problem is the CCV lines, and orifice are clogged up on the small line side between the cover and intake manifold, and the other vacuum lines are leaking. A leaking valve cover gasket, on VC top side seals (oil filer, big breather tube) contributes to the problem too!
Fix the CCV and vacuum lines, then run a compression test, if wet compression is below 120, then try Restore. Also try a higher weight oil. I run 20W-50 in mine.

Then if all that fails, and compression is down to like 100, then pull the head, but do a leak down test first, to decide if you need valve and head work, or rings too.

I fixed my blow by problem on my old 88 about 3 years ago now. I was getting at least a quart of blow by every Hundred Miles. If you have ever removed the stock valve cover on a renix then you can easily see why there is such an issue.
The dummy who designed this cover put an aluminum tube that goes down to the oil vally in the top of the head. So you have these tubes which are very very close to the top of the head... If you have any kinda gunk built up in the oil returns (and YOU DO) then these tubes are down in the pooling oil. Now with these tubes having vacuum lines on top of the valve cover to suck out any built up pressure, they instead suck up the pooling oil. So here is how you fix the blow by problem for good!
1.Run Seafoam in oil for an hour at idle.
2.Pull valve cover
3.Pull oil drain plug
4.Get some good parts cleaner and a few different brushes a can of carb cleaner helps a lot too
5.Clean the top of the head and the oil returns
6.Pour another can of Seafoam on top of the head
7.At least take the aluminum tubes off of the old valve cover and clean it very good! I put the Crown valve cover on and started with a nice new red one. It has Baffles in it over the ports for the vacuum tubes. Make sure you don't use the screws that come with it. Tap out the holes with a 10-32 machine screw tap and install new screws. It comes with small wood screws holing the baffles on.
8.Reinstall the valve cover and use a valve cover breather instead of the small orifice and hard tube on the back and on the front. The old grommets will not fit the new crown cover. Use Mr. Gasket # 2057 breathers, only ones i could find that fit. You will also need to get new grommets in the HELP section of a parts store. New Head doesn't come with them.
9.Cap the vacuum lines
10.Put fresh oil and filter in it, let it idle for about an hour again
11.Change oil again to get any of the crap from the head out of the engine
12.Enjoy not having any oil in your air box, or running out of breathers. I GUARANTEE that you will not have the Vacuum Sucking Oil into the Air Box , i.e. Blow By problem any more.

1985xjlaredo,

I forgot about that. Good post. I cleaned out the valve cover down spouts area on both of mine too, when I replaced the valve cover gaskets. Makes a big difference. They get really crudded up inside, and that oil pool really sucks!:laugh2:

However, I stayed with the OEM valve cover (just cleaned it completely), and installed a new OEM CCV vacuum line set, like many others here with no problems since.