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Unread 05-13-2008, 12:43 PM   #1
TheMightyGoat
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Some vent that might be related to rear main seal leak?

I have a slow leak in my rear main seal. I was getting ready to change it and a mechanic I know told me that I should check a vent before I do that as it might be plugged, causing the seal to leak under pressure. My guess is that even if this is the case the seal will have to be replaced eventually now that it has leaked, but regardless, what's this vent he's talking about? I may as well make sure it's clear. Where do I find it?

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Unread 05-13-2008, 12:49 PM   #2
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Sounds nutty to me,but what do I know.
http://www.dailydriventj.com/forum/viewtopic.php?t=811
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Unread 05-13-2008, 01:09 PM   #3
Crashnburn80
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Your mechanic is refering to the PCV valve, Positive Crankcase ventilcation valve.

However the rear main seals on the 4.0 are not very reliable.
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Unread 05-13-2008, 01:21 PM   #4
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I'm on my 3rd rear main at 43k miles, and I noticed its started leaking AGAIN. good thing its still under warranty.
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Unread 05-13-2008, 01:23 PM   #5
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Quote:
Originally Posted by Crashnburn80 View Post
Your mechanic is refering to the PCV valve, Positive Crankcase ventilcation valve.

However the rear main seals on the 4.0 are not very reliable.
I thought they didn't have a PCV valve and it was just an elbow
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Unread 05-13-2008, 01:26 PM   #6
Crashnburn80
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Quote:
Originally Posted by Theboogieman View Post
I thought they didn't have a PCV valve and it was just an elbow
To be honest, I've never really paid much attention to it. The FSM does specify to inspect PCV in the mainenance schedual though.
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Unread 05-13-2008, 01:27 PM   #7
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Quote:
Originally Posted by Theboogieman View Post
I thought they didn't have a PCV valve and it was just an elbow
Thats correct. There is no PCV valve.
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Unread 05-13-2008, 01:59 PM   #8
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The elbows and the pipes can get clogged.
If there is no airflow from the airbox intake thru the crankcase and back into the intake, the positive pressure created by piston ring blow-by can cause the rear seal to leak (also the valve cover).
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Unread 05-13-2008, 02:59 PM   #9
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Quote:
Originally Posted by Crashnburn80 View Post
To be honest, I've never really paid much attention to it. The FSM does specify to inspect PCV in the mainenance schedual though.
Thanks,I try to learn from you and others.
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Unread 05-13-2008, 03:59 PM   #10
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My jeep does not have a PCVV (PCV valve), but it does have PCV (positive crankcase ventilation).

If the PCV system was clogged it could cause the pressure problem/leak, but I'd say it's unlikely, but check it out before you go to the effort to replace the rear main.
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Unread 05-13-2008, 05:19 PM   #11
TheMightyGoat
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Quote:
Originally Posted by Wif View Post
The elbows and the pipes can get clogged.
If there is no airflow from the airbox intake thru the crankcase and back into the intake, the positive pressure created by piston ring blow-by can cause the rear seal to leak (also the valve cover).
So I don't have a valve, but the system vents somewhere? The seal is leaking very slowly and it hasn't left a puddle anywhere when parked (even for more than a day at a time) since I've noticed it - presumably it only leaks when driving, and not much at that, as I haven't had to add oil to it yet. So my first inclination is to think it would be leaking more if there were a clog in the system. But, it's probably worth checking out. I'm going to go see if I can find anything about the PCV in my repair manual.
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Unread 05-13-2008, 08:57 PM   #12
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All engines create fumes (exhaust getting past valve stem seals or piston rings). If the crankcase was sealed tight there would be oil blown out of every seal / gasket. These fumes need to be drawn off and burnt.
For this to happen there has to be a system in place that allows fresh air to be drawn in, and stale fumey air to be drawn out.
On the valve cover there are 2 take-offs. One allows fresh air in (normally connected to filtered side of the air box), the other is connected to the vacuum side of the intake. This ensures that all fumey air is drawn back into the combustion side of the engine and burnt off. There is a restriction in the vacuum side to ensure there isn't a large "leak" that would make the engine run lean under certain throttle conditions. On older PCV systems this was vacuum operated PCV valve.
If there is a leak or a blockage on the vacuum side the fumes won't be drawn off and pressure can built up in the crankcase.
The easiest way to check this is working is to pull the fresh air side off and see if there is a vacuum being pulled back into the engine.
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