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waltrobak 11-11-2013 09:57 AM

Rear Main Oile Seal Leak
I have a 4.6L 2V motor from and 01 GT with 51K on it that I transplanted in to an 87 Jeep Wrangler. Before I dropped the motor in I replaced most of the gaskets and seals including the rear main oil seal. I installed a new National Teflon oil seal. I just started the motor with the access panel on the tranny removed and after the oil is fully heated up I can see an occasional spurt of oil run down off the bottom of the seal. It does not come out fast, it is actually a very very slow leak. After a 1/2 hour with the motor running there is a little bit starting to drip off the tranny.

I am wondering if this is just normal for these motors. My wife has an 02 Mustang GT and that also has a very small drip from the exact same area with only 70K miles on it. If this is not normal what could be causing it and what can be done to fix it without doing the most obvious. I tried changing the oil to a 10W 30 and that did not seem to make any difference with the leak, but it definatley boosted the oil pressure. Thanks for the help.


dawson1112 11-11-2013 10:17 AM

When you changed the seal , how did you remove the old one?

I have seen guys use a screwdriver to pry it out, nicking the crank or gouging it. Then it will always leak in that spot.

waltrobak 11-11-2013 10:23 AM

When I replaced it I did not go anywhere near the crank. I had the motor on the floor, so I removed the entire back plate first, then I pulled the old seal out and pressed the new one in. At that point I reinstalled the seal plate. It seemed to slide back into place very nicely.

dawson1112 11-11-2013 10:37 AM

lol I forgot you 4.6 guys have the luxury of removing the entire back plate.

Did you use some new oil to put on the seal before sliding it over the crank?

Assuming you wiped any FM from the the crank, and used some fresh oil to coat the rubber part of the seal, Id say give it a few miles to seal up. Ive replaced several rear main seals over the years in the 5.0l engines and sometimes they leak for a few miles then quit.

The only time I have had one continue to leak is if someone before me had changed it and nicked the crank getting the old one out, or the spring in the seal had come out and worn a groove in the crank. Then its a matter of getting a rear main repair sleeve to go on the crank.

71_340 11-12-2013 06:21 AM

Did you take a look at the crankshaft where the seal rides? Although, unlikely at 51K miles there cut be a slight groove. I had that problem on a Crown Vic I used to own and fixed it with a repair sleeve.

Another possibility is that the new seal wasn't installed square.

waltrobak 11-12-2013 07:27 AM

I checked out the crank when the plate was removed and it appeared to be perfect, I did use new oil when I slid the new seal into place and the seal appeared to go into the plate pretty flat. I have been told that they should not leak at all once they are installed, but I guess I will take your suggestion and run it for a while and see what comes of it. I am in no hurry to remover the transfer case and tranny or pull the motor to replace it yet. I just got it all together so I will see what happens. Thanks for all the help guys.

dawson1112 11-12-2013 08:34 AM

Replace/check your pcv valve if its pluged or not functioning the crank case can become over pressurized and push oil out the seal. Usually they don't leak when new, but that's not the rule lol . If it hasn't stopped leaking after a couple miles and the pcv is functioning properly then something happened to the seal when you installed it or the seal is just faulty. Im not familiar with national seal , I always use felpro.

waltrobak 11-13-2013 06:16 AM

I have replaced almost everything on the motor from seals to gaskets and even most sensors, just to make sure that I do not have to do it anytime soon while it is in the vehicle. The one thing that I have not replaced is the PCV and it sat for at least two years. I am going to try that next, thanks for the help.

[email protected] 11-13-2013 08:52 AM

Did you replace the seal and "slinger"? That's a two piece seal on the mod motors.

The 6710 is the seal and the 6310 is the "slinger" which I think is actually a poor description but that's what Ford calls it.

If you only replaced one then odds are that's why it's leaking.


waltrobak 11-14-2013 08:36 AM

You know I am not sure at this point. I did it about a year ago, but I do not remember there being two parts. I know that I only ordered the seal and I remember pressing the seal into the plate, but I do not remember any other part. Does the slinger get pressed in like the seal? I am confused by the diagram, because if I remember the seal pressed in from the outside or back of the plate inward. The diagram looks like the seal gets pressed from the inside toward the back with the slinger between the seal and the plate??? After I pressed the seal into the plate and installed the plate I do not remember adding anything else, in fact when I pulled it apart I don't remember there being anything but the seal present. I am a bit confused.

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