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Unread 07-11-2013, 06:46 AM   #1
jdhaas3
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2008 JK Wrangler 
 
Join Date: Mar 2013
Location: Chesapeake, Virgina
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PCV - Potential Blowby - Bad Rings?

This has been my ongoing problem with my jeep, trying to get it resolved once and for all.

To start, I have a 258 out of a 1980. It runs great, clips down the highway no problem, starts up the first time, overall just runs great. When I drive it around town (anywhere but the highway) it is fine and the PCV system seems to work great.

I used to have a little filter can installed on the valve cover instead of a breather line going to the air cleaner. When I get on the highway and run at a higher RPM for extended periods of time, my engine would be covered with a mist of oil. So I replaced that with a new grommet, new nipple in the end of a hose and ran that to the new air cleaner with the hose hooked up to it. Now I am getting oil pushed up the breather line into the air cleaner. The oil pools up in there and drips on the header every now and then and causes smoke and the burning oil smell, so this isnt a good option either. When I drive locally, I can go all day and no a drop of oil will come up from this breather tube.

The PCV valve is new and works, vacuum is being pulled at the valve. When I put it in the valve cover, I can feel no vacuum being drawn at the other end. I dont leak any oil out of any other spot on the engine, not the dipstick or the other common places I have seen it. It only comes out of the breather hole and only when I run down the highway.

When I installed my HEI setup I checked the compression and it was surprisingly good, 150 in all cylinders and none of them lagged. Since I have good compression, and it only happens on the highway can I rule out bad rings? I will post pictures when I get home from work. For the time being I just ordered a breather can from summit to install inline on the way to the filter for the oil to collect in so it isnt dripping on my header. Please help! As always, any and all advice is appreciated! Thanks.

-James

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Unread 07-11-2013, 09:40 AM   #2
texas1al
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I too have a great running 30 year old engine that has blowby like you describe. I've never done a compression check on my engine, but it sounds like your numbers checked out well. I've always just heard that excessive blowby is a fact of life on older 258's, but I'm also curious to hear how good performance and excessive blowby can co-exist.
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Unread 07-11-2013, 10:17 AM   #3
jdhaas3
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I dont even know if it is blowby, I would think if it was due to blowby it would happen all the time, just not on the highway.
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Unread 07-11-2013, 11:37 AM   #4
gwolff
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Quote:
The PCV valve is new and works, vacuum is being pulled at the valve. When I put it in the valve cover, I can feel no vacuum being drawn at the other end. I dont leak any oil out of any other spot on the engine, not the dipstick or the other common places I have seen it. It only comes out of the breather hole and only when I run down the highway.
Check the inside of your valve cover where the PVC valve baffle is. Might be gummed up if it's not pulling a vacuum.
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Unread 07-11-2013, 02:23 PM   #5
Neuner-9R
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Quote:
Originally Posted by jdhaas3 View Post
I dont even know if it is blowby, I would think if it was due to blowby it would happen all the time, just not on the highway.
May get a lot of this but mine acts the same as yours. Difference is that I have a breather that spits out some oil when under strain. I see evidence of blow-by from the breather when it gets up around 2000 rpm.

Just like you said, I'm fine driving around town for quite a while, but once I get on the highway is when it acts up the most. I think this is from the extra strain from pushing it at a higher speed, fighting the wind. I recently took a 3 hour trip taking back roads out of town. Engine ran great. I hit the highway to come back and that's when it started running hotter, etc.

*edit* Forgot to mention. I recently replaced my canister and with a different style. Evidence of blow-by and oil out of the breather has really decreased.
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Unread 07-12-2013, 09:22 AM   #6
CJ7VFR
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My 1985 CJ-7 with the AMC 150 4 cyl engine does this also.

When I had the breather line that comes from the grommet at the back of the
valve cover running up to the aircleaner with the little filter inside
the aircleaner housing, and ran my Jeep on the highway, I would get all kinds
of oil up inside the aircleaner housing.

On colder days, when the engine would have more condensation in it as it warmed up, I
would also get the whipped up foamy oil residue blown up in there. What a mess!!

I switched to one of the plug in type breather elements that you insert into the
valve cover to try to stop this.

It did, sort of. Instead of blowing oil into the aircleaner, it blew it all over the top
of my engine!

So, what I did was, I made myself an oil catch-can. It has one hose that comes out of the
valve cover hole where the original breather hose came from, and it goes to the catch-can.
And the other hose comes out of a drain plug in the bottom of the catch-can so I can empty it.
I attached the push in breather that I had put into the valve cover hole from before into the
top of the catch-can so the engine would be able to still vent.

Since doing this, it has eliminated any oil pushing up into the aircleaner, as well as getting all over
the top of my engine. I drain it about once a month in the warmer weather, and about once
every two weeks when its cold outside when there is more condensation build up in the engine.

If anyone wants to know how I did this, I can do a quick write up about it.

It was easy, cost me about 15 bucks in parts and hoses, and took an afternoon to put it
all together.

Jim
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Unread 07-12-2013, 10:25 AM   #7
gwolff
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Pcv line should never run to the air cleaner. Goes in the carb below the throttle plates. All that oil and blow by is now gumming up your carb ventureies, throttle plates, etc.One line, PCM, has vacuum, the other needs just a filtered air source.
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Unread 07-12-2013, 11:14 AM   #8
CJ7VFR
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Quote:
Originally Posted by gwolff View Post
Pcv line should never run to the air cleaner. Goes in the carb below the throttle plates. All that oil and blow by is now gumming up your carb ventureies, throttle plates, etc.One line, PCM, has vacuum, the other needs just a filtered air source.
Yes. You are right.

I am refering to the breather line that comes off the back of the valve cover that
routes up to the air cleaner housing. Its all part of the PCV system.

But I will fix my post to clear it up so people don't think I meant the line with
the PCV valve in it.

Thanks.

Jim
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Unread 07-12-2013, 12:58 PM   #9
gwolff
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Quote:
Originally Posted by CJ7VFR

Yes. You are right.

I am refering to the breather line that comes off the back of the valve cover that
routes up to the air cleaner housing. Its all part of the PCV system.

But I will fix my post to clear it up so people don't think I meant the line with
the PCV valve in it.

Thanks.

Jim
Sorry, if that's the case, as described above, make sure the vacuum from the pcv is pulling all the way into the valve cover. I've had it happen before and the blowby will find an escape point. Valve cover inlet into carb, dipstick, blow out a rear main seal or from oil pan seal,etc.
Kind of like a ridge vent on a house. Hot air has to escape but still needs soffit vents for circulation FWIW.
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Unread 07-12-2013, 01:28 PM   #10
CJ7VFR
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Quote:
Originally Posted by gwolff View Post
Sorry, if that's the case, as described above, make sure the vacuum from the pcv is pulling all the way into the valve cover. I've had it happen before and the blowby will find an escape point. Valve cover inlet into carb, dipstick, blow out a rear main seal or from oil pan seal,etc.
Kind of like a ridge vent on a house. Hot air has to escape but still needs soffit vents for circulation FWIW.
I made my catch-can because there was no longer good vacuum at the breather in the valve cover due to the blow-by.

I would rather have it collect and be able to drain it, than have it build up inside my aircleaner and thus get into the carb, or have it blown all over my engine.

Unfortunately, with the amount of miles on the engines we are talking about, that escape point seems to almost always be that back breather in
the valve cover, or the dipstick tube like you said.

Jim
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Unread 07-12-2013, 04:02 PM   #11
gwolff
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That is a lot of blow by if it's more than the pcv can pull into the manifold. Is it fowling your plugs also?
When my sister bought her 85, it had a lot of blow by also. The vacuum line with the pcv valve had caked up over the years as well as the baffle in the valve cover. I also did the old sea foam/cleaner trick after the engine is warmed up to slowly pour the liquid down the carb. Did about half the can and let it sit a few hour and did the rest. It had been so long since the po had driven it, the rings had stuck/carboned up. Used a good hi detergent oil and it gradually got better by the week until blow by was negligible.
Greg
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Unread 07-12-2013, 04:24 PM   #12
CJ7VFR
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I replaced my valve cover a few years ago, because the plastic was starting to crack
around the hole where the oil fill cap goes.

So its clean on the inside. Nothing caked up.

My plugs are o.k. They don't come out smelling of gas or anything like that. And my
Jeep passes inspection no problem.

My engine has about 209,000 miles on it, and its never been cracked open.

I do have a slight leak at the rear main seal that has been dripping just a few
drops here and there over the years.

My poor engine is just tired, and I am sure the rings are shot. I haven't done
a compression test lately, but I am sure this would show the rings are bad.

My Jeep runs great, starts up every time, and chugs along just fine down the road.

If it wasn't for the catch-can, I would be leaving a trail of oil everywhere I bet!

Jim
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Unread 07-17-2013, 07:09 AM   #13
jdhaas3
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Quote:
Originally Posted by CJ7VFR View Post
I replaced my valve cover a few years ago, because the plastic was starting to crack
around the hole where the oil fill cap goes.

So its clean on the inside. Nothing caked up.

My plugs are o.k. They don't come out smelling of gas or anything like that. And my
Jeep passes inspection no problem.

My engine has about 209,000 miles on it, and its never been cracked open.

I do have a slight leak at the rear main seal that has been dripping just a few
drops here and there over the years.

My poor engine is just tired, and I am sure the rings are shot. I haven't done
a compression test lately, but I am sure this would show the rings are bad.

My Jeep runs great, starts up every time, and chugs along just fine down the road.

If it wasn't for the catch-can, I would be leaving a trail of oil everywhere I bet!

Jim

I wasnt leaving a trail of oil, it would just mist all over the engine bay. I did the catch can idea, I ordered a breather tank from summit with a filter already installed on the top and just ran the hose to that for the breather line. Just mounted it on the insdie of a fender so it looks clean and catchs any oil. Pretty nice setup, has a ball valve on the bottom that will let you drain it if it gets oil in it. If i have a little blowby I dont really see the point in breaking this engine apart to fix it, runs great and doesnt leak anywhere...except out hte brether line.
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Unread 07-17-2013, 08:23 AM   #14
Neuner-9R
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Quote:
Originally Posted by jdhaas3 View Post
I ordered a breather tank from summit with a filter already installed on the top and just ran the hose to that for the breather line.
Thinking about doing this. Which one did you get? Assuming you used a 90 degree elbow at the valve cover? I'd need to find one of them.
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Unread 07-17-2013, 11:00 AM   #15
dirtdudeaz
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Posts: 497
It could be blow-by. My engine was at about 130K and when I opened it up (had the same high rpm/WOT engine bay spray) I noticed the rings/pistons/bearings were about on their last limb. I haven't finished the rebuild but suspect this was part of my issue.

Here are my thoughts:

1) I had heard somewhere along the way that these 6 cylinders have this issue at WOT and higher RPMS (highway driving) and it was part of the design. Here is something I found:
Per the TSM: "During periods of low manifold vacuum, such as heavy acceleration, a calibrated amount of air is reverse flowed through the air flow (PCV) valve. Crankcase vapors are then drawn through the air cleaner element and burned along with the fuel-air mixture." I guess if you have blow by and this backflow happens, it would spray oil everywhere? Otherwise with no oil blowby, it would be just air?

2) Check your compression with oil. Check your cylinder compression dry and then measure a small amount of oil and pour it into the spark plug hole. Cycle the cylinder a couple times and take your compression reading again; you should read higher than what it was dry. If it is the same, then your rings/pistons are warn out.

3) If you use an emissions canister make your PCV circuit is working right and that the canister is not worn out (purge circuit and other circuits).

4) If you have older emissions stuff on (miles of tubes and switches) make sure the pcv shutoff solenoid is working, or replace with a straight through tube.

5) Check any areas on the top of the motor that would let air in such as the oil filler tube or cap, valve cover gasket, etc... This would cause air to get in and not let the PCV work that well.

6) If you don't have any emissions stuff on it, your pcv is not stuck closed, your grommets are new and tight, and you get oil coming out at WOT or high RPM, I would think rebuild time.
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