7.3L Diesel Rear Main Seal

N. TX Tim

Member
I have a 1999 F350 with 7.3L diesel and auto trans. The rear main seal started to leak a bit. I checked and it was not the HPOP leaking instead. I took it to a local (non-Ford) shop and he concurred that it was the rear main seal. I had him replace it and he used a brand of seal from O-Reilly"s that he said was made by Fel-Pro. The new seal leaked. He pulled the tranny again and it appeared that the seal was leaking between the outer seal ring and the metal housing that holds the seal in place. He said both he and the O-Reilly"s manager agreed the seal was defective. He replaced the seal the second time with another seal of the same brand. It leaked and again he felt the seal was defective. The third time he replaced the seal with a genuine Ford seal that installed with a sleeve over the crank. About 50 miles on the truck and it appears that it is STILL leaking.

He said that the case may be over pressurizing due to a plugged vent on the valve cover and was supposed to check it, but it does not appear that he did so.

Anyone have any ideas why this could be happening? I really don"t think it is shoddy work. The guy has stood behind his work and not charged anything other than the initial bill.

Any help would be greatly appreciated. I am at a loss and quite frustrated.

Thanks, Tim
 
How many miles? Could be the mains bearings if it has hight miles. Could be the vent. Are you useing synthetic oil? I put synthetic in a perkings one time, Rear seal started leaking replace seal with a new one, Stilled leaked, Sold the rig that the engine was on and never thought about the synthetic oil causeing it till after I sold it. Thing was it never leaked out the rear seal til I put the synthetic oil in it. Was a rebuilt engine to boot only had bout 500 hrs on it.
 
Hello N. TX Tim,

Seals are usually all installed and lubed as a matter of course. That is not always the thing to do. Some seals are lubricated at the lip and at the mating surface. Others are put in (DRY).
The package will have the instructions. There is a reason for the dry seals not to be lubricated. If seals that are designed to be installed dry are lubricated, they usually won't make a good seal and eventually leak. Maybe that simple! By the way Fel-Pro is always been top notch in my book. Never had one fail!

Guido.
 
it's not the syn oil making the seal leak.

my 99 f450 has 130k on it. it had amsoil in it 100% of the time till about 2010 then i switched it to valvoline premim blue syn.

100% dry.. never has ever put a drip on the concrete.

my 99 f350 had 'whatever' oil in it till about 2011 then now has that same valvolene blue syn oil in it. engine does not leak.. trans drips a couple drops a week.. nothing I'm bothered about. that truck is about 191K

it's NOT the oil..
 
Glad it worked for you. Myself I"ll never ever look at the chit again, Besides Soundguy, Just cause You say "It"s not the oil" Don"t mean it wasn"t.
 
I have got about 205K miles on it. I am the original owner and have not put synthetic in the motor. I just pulled the vent and it is clean and air passes through it easily.
 
and because you say it is doesn't mean it is.

at least I have 2 examples to look at.. one with syn oil in it it's entire life... that 450 has had syn oil since the day after it rolled out of the factory after the stuff it came with was drained out.

too many people blame and attribute absurd things to situations without sufficient evidence to carry the argument.

Back in the middle ages they thought tomatoes were poison and that frogs were born out of mud and flies came from rotting meat. they say some limited but incomplete cause and effect and missed a few important issues inthe middle before drawing a conclusion. Oh yeah.. earth ain't flat either.. not anymore... :)

I'd think a new engine.. or a rebuilt engine would be a good candidate for a syn switch.. vs an aged one.

no way to post diagnose your rig now.. but i'd blame the rear seal or the install or the retainer or the sealing surface before I'd balme the oil.

I've seen many replaced mains on tractors only to see an annoying drip... oil would be on the last of a list for what I would think the cause was attributed to.
 
Tim, let me throw some ideas out. Im sure you or your mechanic checked, but ill still say what came to my mind.

1. Is the crank scored where he seal rides on it?
2. Are you sure it is not a oil leak from the turbo base?
3. Are you sure the leak is not diesel fuel from the lift pump?

A scored crank just won't hardly seal. There are two o rings between the turbo and the intake. Those o rings can dry out and crack causing a major oil leak. I've also had leaks I swore were rear main until a closer look (smell) revealed a leaking lift pump.
 
no pee'ing match.. you posted an observation.. I posted an observation.. If you did want any other possible opinions posted.. you could have said so in your post.
 
All good suggestions from knowledgeable folks. For more good info try the PowerStroke forum. They have some good Ford techs that participate. Might be able to add more.
 
FYI I was just surfing around on the net, looking for what I could find about a fuel filter leak on my brothers 91 7.3 when I ran across a very nice video describing how a lot of folks were blaming rear engine oil seals for leaks when they were actually coming from somewhere else. It was a very good video with pics of where the leaks could be coming from. Might be worth the trouble to look it up. EGBinOR
 
Since he's pulled the tranny, I'm sure he's verified it's still the rear main seal. I would check the crankshaft sealing surface. Clean it up with crocus cloth or a 600 grit sandpaper. Get it clean with with starting fluid or brake cleaner. Inspect for any scoring. Check crank endplay. Usually it's under .015. If he's installing a teflon seal MAKE absolutely certain no oil is on the sealing surface before installation. Otherwise lube it with clean engine oil. Some engines REQUIRE rear main seal installation tools. Find out from Ford. In my experience excessive crankcase pressure caused more than one seal to leak. It didn't just cause the rear main to leak. Hope this helps. Gerard
 
(quoted from post at 19:55:45 03/24/13) FYI I was just surfing around on the net, looking for what I could find about a fuel filter leak on my brothers 91 7.3 when I ran across a very nice video describing how a lot of folks were blaming rear engine oil seals for leaks when they were actually coming from somewhere else. It was a very good video with pics of where the leaks could be coming from. Might be worth the trouble to look it up. EGBinOR

Fuel drain valve orings are a good one for that. People expect it to be green, but it turns black by the time it gets to the bottom of the engine so they think it's oil. The tell tale sign on that one is all kinds of fuel in the valley.

Where does the HPOP leak? Mine has oil leaking down by the starter.
 

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