Blowby/PCV?

Hello all,

My XJ has over 300,000 miles on it, and has pretty bad blowby. I've replaced all the vacuum/CCV lines, cleaned the valve cover and the fitting on the manifold. I've done everything I can think of without making any major mods, and nothing seems to help, it still blows oil into my airbox. I was wondering if anyone has tried putting a PCV valve in the hose going from the valve cover to the airbox, to stop air flow into the airbox and try to force it to go through the smaller CCV lline to the manifold (like it's supposed to in the first place). Tell me what you'll think, could it work or am I asking for more trouble?

TIA,
Darin

A PCV valve will not help you. Basically your problem is your rings are worn and when you piston travels up for the compression stroke some of the cylinder pressure escapes past the rings and causes a positive pressure in the crank case. This positive pressure causes air from the crank case to be pushed out of the vents in the valve cover into your air cleaner where it is sucked into the intake and burned in the combustion process. As you have noticed there is quite a bit of oil vapor in the crankcase and it collects in the air filter.

Short of a rebuild there is little you can do. One thing you could do is put a catch can between the valve cover and the air cleaner to condensate and catch the oil before it gets to the air filter housing. It really doesn't fix the blow by but it does keep the air filter clean. At over 300K it's likely time for a replacement motor though.

HTH,
B-loose

So you don't think a PCV valve, installed in reverse of the way one would normally be installed, would restrict air from flowing from the crankcase to the airbox, while still allowing air to flow from the airbox to the crankcase as it should? If not a PCV valve, what about some other kind of check valve? Or could this result in blown gaskets if the smaller CCV line isn't able to relieve enough of the pressure in the crankcase?

FYI, I only intend this to be a temporary fix to get me by until I can afford to either rebuild the engine, or replce it.

Thanks,
Darin

Just put in a puke tube. As said above, that much blow-by is the product of a worn engine. Puke tube into a catch can is the only way to deal with it without a rebuild on an engine with that many miles.
BSD

Can't you just run it as is?

You might have done it already, but you didn't mention it. Clean the Orifice in the CCV fitting itself. The Orifice gets gummed up as well, just unscrew it from the valve cover and poke a pipe cleaner thru it and clean it up well.

You can clean up and replace everything to make a clear path, but if that little orifice is gummed, restricted or blocked, you'll still get the blow by, because its preventing or restricting the vacuum to the crankcase.

Bloose said:

Can't you just run it as is?

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Yeah, that's what Ive been doing, but I'm leaving on about an 800 mile trip tomorrow (or is that today). For normal local driving it's no big deal, I loose maybe a quart of oil a week at most, but on a trip like this that will be more like a quart a day, at least!

Rick Anderson said:

You might have done it already, but you didn't mention it. Clean the Orifice in the CCV fitting itself. The Orifice gets gummed up as well, just unscrew it from the valve cover and poke a pipe cleaner thru it and clean it up well.

Click to expand...

Yes I replaced that at the sametime I replced everything else.

Well, thanks for all the replies. I'm gonna give the catch can a try.

Many thanks,
Darin

with your millage that is prbably correct but to other people with less than 150k there is something you can do. check my post on oem

Putting a PCV valve in there would just end up pressurizing the crank case and you'd leak oil everywhere else.

do a google search for a oil check valve or breather check valve for a buick turbo V-6 or grand national if you have to have one. The easiest fix is to find a valve cover breather that fits in the oil fill hole or one of the other holes and plug ff the other end.

Now I'm not recommending this but my mechanic suggested I just cap off that tube where it connects to the airbox and run it like that. Which I did, and I have same amount of miles on my '91. Ran it like that for a few years without any issues. Maybe yours will accept that fix.