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Old 12-22-2012, 02:01 PM   #1
uncle.stosh
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Rear main seal leaking after changing PCV?

I've always had a slight drip from my rear main seal, but yesterday after finally putting in a new PCV valve it is leaking really bad.

I was about a little over half a quart low on oil from the leak. After topping off the oil and putting in the new valve it is leaking worse now than it ever has.

I know it's possible that the new PCV valve is bad, but I can hear the ball rattle around inside it and seems to be fine.

Do you guys think that it's just coincidence that my rear main has finally gone completely or am I overlooking something here? Should I just remove the PCV valve from the valve cover and see if it goes away? I know that if the engine is building internal pressure and it can't go anywhere that major leaks can occur.

I really don't want to pull the transmission and transfer case, but that's my only choice at this point.
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Old 12-22-2012, 02:16 PM   #2
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The old PCV valve was probably worn out and not holding as much pressure as a new valve. It sucks changing one, but its routine maintenance.
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Old 12-22-2012, 02:20 PM   #3
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routine maintenance.
Changing a rear main seal is routine maintenance? Oh boy.....



I knew I was going to have to change it eventually, just wasn't looking to do it right now.

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Old 12-22-2012, 02:21 PM   #4
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This would be easier if your ENGINE was mentioned in your profile or signature.



But I think it's coincidence. A new PVC allows higher vacuum in the crankcase, which would hold the oil in better, even at a leak. With the engine idling, pull the vent line off the oil filler neck & plug the nipple. Vacuum should slowly build up. Don't let it go any higher than is necessary to detect it, or you could damage the seals. If you can rig up a vacuum gauge to it, that would be better since it's more precise than a finger. If nothing happens on the L valve cover (assuming it's a V8), lift the PCV out of the R one and see if there's vacuum at its crankcase port.

It's also possilbe that the leak isn't actually coming from the rear main. It could be from a rupture in the cam bore plug or from the bolts in the crankshaft flange not being sealed. Have you looked at the rear intake valley seal? Use a flashlight & mirror, or borescope.
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Old 12-22-2012, 03:18 PM   #5
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Sorry, I thought I had the engine info filled out.

It's a 5.0L engine.

It's always dripped a little from what I thought was the rear main seal. Today it's so bad it's pouring on the Y pipe and smoking pretty bad.
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Old 12-22-2012, 04:06 PM   #6
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Sure it's not the garbage OEM 4 piece pan gasket? Always replace them with the one piece. Very difficult to fully remove the pan on our Broncos but you can do the job by just getting it down as far as possible. Also a good time to wipe the trash out of the pan bottom. It WILL have a bunch of black crap from disintegrating valve guide seals that if left alone will eventually clog the oil pickup screen (and if you're travelling at highway speed and don't notice the gauge reading zero) and wipe out your engine. Usually the main bearing leak will be dripping out of the torque converter area where the pan leak is between the engine and tranny and ends up on the y-pipe.
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Old 12-22-2012, 06:05 PM   #7
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I'm going to try and clean it up really well tomorrow and see if I can find out where it's leaking.
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Old 12-22-2012, 07:30 PM   #8
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Sorry, I thought I had the engine info filled out.
Well, you still don't. When you post it, no one knows which post to go looking for to find that info. You have to put it IN your profile &/or sig so it appears with each post.
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Old 12-23-2012, 12:29 PM   #9
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Happy now Steve? LOL

There is only one hole in the passenger side valve cover where the PCV valve is.

I'm not following your test procedure. Can you clarify please?
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Old 12-23-2012, 03:29 PM   #10
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The PCV, even if it was plugged, would not pressurize the crankcase because the blow by would exit into the air cleaner. Your oil leak increase at the same time as the PCV change is a coincidence. What people believe is a failing rear main seal, is usually is something else. Check the valve covers at the rear, the intake manifold at the rear, and the pan gasket at the rear. If all those areas are dry, zero chance, then maybe you have a leaking rear main seal.
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Old 12-23-2012, 03:46 PM   #11
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The PCV, even if it was plugged, would not pressurize the crankcase because the blow by would exit into the air cleaner. Your oil leak increase at the same time as the PCV change is a coincidence. What people believe is a failing rear main seal, is usually is something else. Check the valve covers at the rear, the intake manifold at the rear, and the pan gasket at the rear. If all those areas are dry, zero chance, then maybe you have a leaking rear main seal.
How could blow by possibly vent to the air cleaner when their is NO hose or anything else connected to it?

There is ONE hole in the passenger side valve cover (other than the sealed fill cap on drivers side) for crank case venting.

Your comments don't make any sense........
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Old 12-23-2012, 07:40 PM   #12
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What is in the 'one hole on the passenger side'? Normally there should be a hose going to the air cleaner so the PCV vacuum can draw fresh, filtered air into the crankcase. I agree with nelbur about other things being more likely the oil leak source. My preferred thing to condemn is the oil pan gasket since the original 4 piece setup is such a POS compared to the newer 1 piece ones. All of our older Broncos need their oil pan wiped out anyway to get rid of the valve guide seal debris.
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Old 12-23-2012, 08:17 PM   #13
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The hole in the passenger side has the PCV valve in it and the hose connects directly to the back of the upper plenum.
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Old 12-23-2012, 11:50 PM   #14
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Regardless,if it's your rear main or any other seal leaking....it's not a new pcv valve that's causing it..if you ran a bad pcv valve for a long time,that may have caused some leaks.

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Old 12-24-2012, 12:37 AM   #15
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You should have a hose from the oil fill cap to the air cleaner, with a mini filter inside the air cleaner so filtered air can be drawn in to replace the air sucked out through the PCV valve. If you have the hole in the fill cap plugged up, you could be building pressure in your crank case if your PCV valve can not keep up with the blow by. Pressure in your crankcase could make your seals leak, so take care of this before you start tearing anything apart. In well worn engines it is common to have oily blow by running backwards through this hose and putting a lot of oil into your pleated paper oil filter. Someone may have taken steps to "remedy" this on your engine.

Edit: I see your 302 EFI is much newer than mine, so your hose that provides filtered air to the crank case may be different than I described, but you should have one of some sort. You might need to look at another engine of your vintage to see what was modified on yours.
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Old 12-24-2012, 01:42 AM   #16
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Happy now Steve?
It's a start...
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I'm not following your test procedure. Can you clarify please?
What's unclear? The goal is to find out if you have any manifold vacuum getting to the crankcase.

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Old 12-24-2012, 10:33 AM   #17
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It's a start... What's unclear? The goal is to find out if you have any manifold vacuum getting to the crankcase.


Thanks Steve for the diagram.

That makes it perfectly clear. I don't recall seeing the vent tube that runs to the air cleaner box.

I'm going to take a good look at it today. Maybe it is my oil pan gasket after all.
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Old 12-25-2012, 04:49 AM   #18
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You need to jack up the engine to swap the oil pan gasket. Without reaching in and unbolting the oil pump and pickup tube there is little chance of getting the pan completely off although all you need do is drop it enough to change the gasket. A wise extra is to put on a new screen unit (around $20) and reaching in and cleaning the bottom of the pan. All our FSBs will have remains of the valve stem seals in there which eventually plug the screen. Good insurance against losing the engine.....
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Old 12-25-2012, 11:58 AM   #19
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What are the recommended ways of jacking up the engine?

I have a cherry picker and can use the factory lift mounts I suppose. I'm not a big fan of jacking it up by the harmonic balancer.
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Old 12-25-2012, 01:10 PM   #20
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PVC needs a CLEAN vent to work proper or the gaskets will suck in !!
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