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Air filter, oil blowback?

W

wildman

NAXJA Forum User
Location
Jennings, LA
I noticed a huge lack of power today while I was taking a little trip down the interstate. I got off on my exit and pulled into the driveway to see what it was.

This is what I found: (pics)
http://www.crawfishdesigns.com/airfilter.htm

I replaced this air filter approx. 1 month ago. When I bought the Jeep, I disconnected the hose from the top of the valve cover, and replaced it with an open/screened filter because of this same problem. This kept the oil from traveling back into my air filter. And seemed to work quite nicely, that is, until the rubber holding that top filter in there went to $h!t and it fell off right before I changed my air filter. What causes this? What can I do? Should I go back to the open filter on top of the valve cover? Was that a bad idea to begin with? any help would be greatly appreciated.
 
An improperly working PCV system will cause that. Make sure the valve is not pluged and that your lines are all in good shape. They are not that expensive from the dealer. If that doesnt help, you most likely have oil blowing past the worn piston rings (blow by).
 
Well, I contacted the dealership about the PCV valve and he told me that my Jeep 'doesn't have one and can't get one'. He said that instead, it is just an open end that fits into the grommet. ??? I hate to say it, but I don't believe that, I have friends with the some older/newer models that all have an actual valve there. How do I know if oil is blowing past the piston rings without tearing it down?
 
holeshot said:
An improperly working PCV system will cause that. Make sure the valve is not pluged and that your lines are all in good shape. They are not that expensive from the dealer. If that doesnt help, you most likely have oil blowing past the worn piston rings (blow by).
Click to expand...

The piston rings have nothing to do with the valve cover. If oil were blowing by the rings it would go out your exhaust, not the PCV system. The system on the renix 4.0 is designed to put crankcase fumes into the intake to be burned. The oil can easily make its way into that hose, there fore dropping oil on the air filter. The only way to get around it that I know of is to use a Chevy style breather filter.
 
wildman said:
Well, I contacted the dealership about the PCV valve and he told me that my Jeep 'doesn't have one and can't get one'. He said that instead, it is just an open end that fits into the grommet. ??? I hate to say it, but I don't believe that, I have friends with the some older/newer models that all have an actual valve there. How do I know if oil is blowing past the piston rings without tearing it down?
Click to expand...

Technically it is not a PCV system. Yes it takes fumes from the crankcase but it doesnt have a valve like other PCV systems. If i remeber right, other systems use the pressure of the building fumes to open the PCV valve, where as the system you and I have uses vacuum from the intake. Don't quote me, as I had this all explained to me four years ago by the Jeep tech that sold me a new "PCV" hose.
 
The piston rings have nothing to do with the valve cover. If oil were blowing by the rings it would go out your exhaust, not the PCV system.
Click to expand...

Wrong.

How in the bleeding hell would leakage past the rings get into the exhaust?

Positive Crankcase pressure is caused by leakage past the piston rings from the combustion chamber (high pressure) to the crank case (low pressure), commonly called blow by. This pressure has to escape somewhere, that is why they put the crank case ventilation system, in the valve cover. If that vent gets plugged, the oil commonly gets forced up through the distributor shaft into the distributor. Too much blowby, even when the vent is open, forces minute particles of oil into the vent, over time, this small amount of oil collects in the hose and is blown into the air filter box.

Technically it is a PCV system. It is positive crankcase ventilation because the hose actually goes to a slightly lower pressure in the air filter. There is actually a vacuum being placed on the crank case. Just because there isn't a PCV valve does not mean it isn't positive crankcase ventilation. The valve got its name from the technique, not the other way around.
 
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I have seen this before on a really worn out rig, (no offense just describing the truck) and the poor guy was 500 miles from home. If I remember correctly, we pulled the tube and grommet out, plugged the nipple on the intake, and replaced the blow-by tube with one of those small Valve Cover Breathers from the rice-rocket section at autozone, only cost like 8 bucks and to my knowledge the guy still runs it today. Seems like we had to look for hours for a grommet to match the breather though....
 
old_man said:
Wrong.

How in the bleeding hell would leakage past the rings get into the exhaust?

Positive Crankcase pressure is caused by leakage past the piston rings from the combustion chamber (high pressure) to the crank case (low pressure), commonly called blow by. This pressure has to escape somewhere, that is why they put the crank case ventilation system, in the valve cover. If that vent gets plugged, the oil commonly gets forced up through the distributor shaft into the distributor. Too much blowby, even when the vent is open, forces minute particles of oil into the vent, over time, this small amount of oil collects in the hose and is blown into the air filter box.

Technically it is a PCV system. It is positive crankcase ventilation because the hose actually goes to a slightly lower pressure in the air filter. There is actually a vacuum being placed on the crank case. Just because there isn't a PCV valve does not mean it isn't positive crankcase ventilation. The valve got its name from the technique, not the other way around.
Click to expand...


Nothing left to say but......"BY GOD"!!!
 
if i'm correct, on these vehicles, it's not called a PCV, but a CCV. and yes the dealer does sell those PCV/CCV elbows, because mine broke several months back, and i found out that it's a dealer only item. if you want, i can try and get you a part number tomorrow.

what year is your jeep?
 
89' 4x4 laredo, 4.0L, 115000 miles

ok, thanks old_man, I understand what you're saying, but what do I do? I am thinking about going back to a cone style filter in the grommet instead of the hose to air filter set up. And yes, it took me quite a while to find a grommet to fit. That way worked fine for the last 30,000 miles and hopefully it will work fine for the next 30,000. Question is, is that like ignoring a potentially serious problem? or is it just a convenient way to by-pass replacing my air filter on a bi-weekly basis?
 
Avoid using Penzoil, pull the valve cover - clean it and the baffles, replace the CCV system and upgrade to a late model design less prone to plugging.

Search here a bit on CCV and/or blow by, and you will get more than enough info.
 
3XJFamily said:
Avoid using Penzoil, pull the valve cover - clean it and the baffles, replace the CCV system and upgrade to a late model design less prone to plugging.

Search here a bit on CCV and/or blow by, and you will get more than enough info.
Click to expand...

Mobil synthetic, pulled valve cover, cleaned everything, tried replacement system, local dealership looked at me like i was stupid. showed me where there was NOT a PCV valve for proof. he was an @$$hole. what late model design is less prone to plugging?
 
I think as a back yard way of checking for blow by you can remove the oil cap from the valve cover when the engine is running. If you have lots of air wooshing out you have some serious blow by. Otherwise, the best and most accurate way would be a cylander leakdown test. It requires a special regulator setup and some compressed air. Similar to a compression test.
 
There is no total longterm fix, but pull the valve cover, take the internal assy in the valve cover apart and clean it very well. Clean the hoses and put it back together again. It should last for quite a while. If you keep the flow high enough, it tends to cut the spitting of the oil through the hose. Another problem that sometimes causes this to be worse is on the earlier Renix units, people pull the restricter where the hose plugs into the air box. It makes the engine breathe better, and gives a touch more power, but that restricter causes a venturi that generates a better vacuum. Without the vacuum, it doesn't bleed off the fumes as well.

What people don't realize is that the reason to bleed the crank case fumes has a second part. Oil break down and its corresponding sludge is caused by water in the oil. When the fuel burns, water is a byproduct. If it blows by the rings the water ends up in the oil. Sulphur in the oil, added to water, and heat equals H2SO4 aka sulphuric acid. This is a major component of oil breakdown and engine wear. By venting the crank case, the water vapor is also purged, cutting down on the sludge.

:lecture:
 
again I say ...."By GOD!!"







If we had a XJ Acadamey Old_Man would be the lead Professor!
 
There are tons of guys that know as much if not more than I do around here. It's what you learn after you know it all that counts. The only difference between me and the newbies around here is that I have had 40 years to learn. There are some 20 somethings around here that would really surprise you with how much they know and have taught me a thing or two. The average level of technical expertise at NAXJA is awesome.
 
I know what you mean, I graduated from NTI (NASCAR Technical Institute) about 5 years ago, and graduated to Master Technician about 2 years ago and I still just keep my mouth shut even if I know the situation very well, I agree that the best way for anyone to learn is to just do it, you'll figure it out.
 
Looks like you guys all have me by a few years, only 17 here, lol. holeshot, I'll check it that way, after I do what old_man said and clean everything out really good. thanks alot
 
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