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During the last two seasons I have noticed a slight oil leak from my stbd. merc 454. Checked oil regularly and never had to add. I thought it was coming from a valve cover so I changed out the gaskets. Last season, still a little oil, but couldn't seem to pinpoint it. Just before I took the boat to get hauled at the end of the season, I cleaned the outside of the engine and the drip pan below to a spotless condition. Got to the marina and spent some time with a mechanic trying to figure out the source. After some investigation, it appeared that the oil was coming from a small gap where the bell housing connects to the block. Mechanic said he thought the rear main seal could be the source. Put the boat to bed and forgot about it.

I am now about 3 weeks away from splashing her back. So, knowing that I would potentially have to pull the engine to replace a rear main seal, what is the possibility that doing nothing would cause a sudden loss of oil pressure thus ruining the engine? It this something I can keep an eye on and address later, or am I taking a big risk on frying the engine as I cruise down the bay at 2800 rpm? Obviously I will eventully have to take care of it. Just would rather do it later in the event that I have to pull the engine for some other reason.

Any thoughts?

Wow, will it fail or will it not??
I'm not the last word but I have never seen a sudden and total rear main failure.
I'm sure it happens, I just haven't seen it. Typically they drip and drip and drip some more.

But hey you have a spare engine!

I've been under an awful lot of transit buses in the last few months. Mostly Cummins ISL and ISM power plants coupled to my gears. Roughly half of the units I look at have rear main seal leaks.
When I ask the techs what they're gonna do about it. They say "Clean em off add fluid and let em run"
As Scot said they don't normally fail catastrophicly but they will continue to leak until you can't stand it.
On the other hand having said that yours will now be the one dumps its guts into the bell housing.
If it were me, I'd fix it now.

On a boat, I would fix it. It is only necessary that it fail when you need it most...

My old Chrysler 440's had the same thing. They always leaked, even after new seals. Apparently it is hard to get them to seat right... Or the mechanic I used had his head somewhere it shouldn't have been, and he was bent over... you get the picture.

Regardless, I ran for a couple years before the engine on the other side blew up for no reason related to the leaking seal... That was the mechanic's fault. The seal wasn't.

Make any sense at all?

Have it done, and enjoy the peace of mind.

An annoying, nasty PITA, but not a cause to worry about sudden failure.

Crae-

I also don't remember hearing of a sudden dump from the rear main...just drip, drip, drip 'til it gets bad where you need to do something. We're Bay boaters---you're never that far from port, so I'd let it go and keep an eye on it.

John F.

I'd forget about it and check the oil often.....the Bride's 97 MB E320 has an annoying engine oil leak that they wanted $2,700 to fix six years ago....naw....bought a $8 gallon of Shell Rotella T to keep at the house, just finished the gallon and got a new one. Same on my 97 Tahoe, small annoying leak out of the front of the engine, add a little oil now & then and clean the garage floor with M-1 detergent every couple of months.

At least it's not a oil slingin' dump truck motor....

UV

let me get this right...your engine only leaks in one spot?....i'd settle for that

I would not worry about it as long as its not making an uncontrolable mess in the bildge.

It will not cause a catastrophic failure........the seal only sees splashing oil and crankcase pressure and not full engine oil pressure.

Another thought...........are you sure that its engine oil????.........whats the chance that it may be gear oil????

The engine rear crankshaft seal and the gear front seal are both housed in the flywheel housing.

A front seal failure on (I am assuming a Velvet Drive)your gear will cause you much more heart ache than the rear engine seal.

Harry

Although I believe you are doing the right thing by being proactive and noticing this... I'd turn my head.

If you are not burning or losing oil frequently enough to have to add between changes, then you have every right to not even notice the smudge in the bilge.

It's a bilge, not a kitchen sink....

check oil with dipstick not with level of cleanliness in bilge.

It may be the seal, it also could be the oil pan gasket. The seal is fairly easy and does not require pulling engine. If you go in to change the seal and then you find out it is oil pan gasket... then you need to consider pulling.

Just not worth it for a clean bilge.

If it is the crank oil seal, it's about 50/50 that a new seal will actually be successful. Most mechanics hate changing them because they often continue to leak. Usually there is a shaft condition that causes the seal to fail, and there is no good way to address this when doing the seal.

good luck,
mike dolan
www.lightningshack.com

Put a bilge diaper under it and forget it!

The 440 engines in my boat where pulled several times because of the seal leaking by the previous owner after a rebuild. Finally he settled in on the fact it will continue to leak and left it at that. I bought boat 13 years ago and she has leaked the same since. I consider it a way to keep the oil fresh, also it lets me know when I am ready for an oil change, oil breaks down and I get more oil leaking then usual. I also was immune to the leak as I grew up on Dads boat with the same issue.

Thanks for all of the feedback guys.

Though I am all about "piece of mind," fixing every little thing on the boat that goes wrong, I think I am going to let this one go and just keep an eye on it. I check my oil before every start up and did not have to add oil last season (though I did do a mid season oil change). The previous owner of the boat constructed aluminum drip pans under each engine, so the bilge stays pretty clean anyway...and yes this is the only leak I have! I rebuild the port engine about 150 hours ago so it is tight as a drum. Leaky stbd. engine has about 700 hrs on a long block installed by the previous owner (had 250 on it when I purchsed the boat a few years ago).

Like UV says, at least they aren't the oil slingn' dumptruck engines- which by the way are very loud too. My uncle arrived at TSL yesterday- told him to bring earplugs if he didn't want to lose his hearing by the end of the week. Amazing that they run those engines every day, all day, for 10 months of the year. I hear they may be going Nani due to the shortage of 453 parts.

Don't loose your hearing.
This is what I did. Last season I took house carpet with a thick pile and installed it inside of the engine covers. Then put more carpet out board of both stringers to the chine. Just two days ago, I installed thick carpet under neath the engines. So what if the carpet gets wet or stained with oil. Throw it out next winter and get some more.
You know what? It's free. I don't keep the extra carpet I have left over. Refuse bin.
The noise reduction is great.

Mack some times you just have to let them be a little nasty...even when it goes "agin" everthing you believe about keeping your stuff in order. I'm the same way. I took the intake manifold off a PCM 350 chevy that I have in another boat 3 times before I decided to let it drip just a bit. I gave up. Turns out the drip isn't even enough to make it all the way to the bilge, wipe it down from time to time.

Tony Athens sent me this shot during his long and no-stop attempt to talk me out of running an older Detroit, I love Detroits but I think he's winning.

No rust tho. And the oil changes itself.

UV