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Transmission Leak?


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During winterizing last weekend, ran the boat up to operating temps before changing the oil.  Since I have owned the boat, I have always had some very minor amounts of oil in the bilge (not a lot) and I chalked it up to weeping valve cover seals and PCV grommets on the valve cover.  Motor is a carb 350 magnum 740hrs (keep in mind my boat is now 20yrs old, it's a 1997 Tantrum).  However this time there was a fairly significant leak coming from the transmission area?

Whats more common to leak?  Could it be the rear main seal?  Or is it more likely the transmission?  It was kinda hard to tell if it was transmission fluid or not, the engine oil was on the dirty side of things, seemed to be the same color as the tranny fluid.  I wasn't about to deal with it (going into storage) but it will need to be addressed in the spring.

I am definitely mechanically inclined, not too worried about dealing with this, just more of a PITA.  Can the tranny be removed without pulling the whole engine?  Or am I looking at a whole engine pull?

 

Thanks crew.

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Thanks.  I assume probably a good idea to measure angles of the propeller shaft before doing so, I take it the coupler can be unbolted and the shaft can be left as is... the tranny will come out without having to remove the propeller shaft?  I also assume you have to jack the rear of the engine up?

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before breaking motor mounts loose scribe current location on the adjusters.

reinstall to the scribe marks and your alignment might be at a good starting point (depending on the accuracy of your current alingment).

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Good tips thanks, yeah I think my alignment might be a tiny bit off anyways, I noticed some very very slight uneven wear on my strut bushing.

Edited by solorex
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My 99 Sportster with around 790 hours has developed a leak in the same area. It only started after I ran synthetic blend oil (Rotella T5) at the start of the season. I thought that may have been the cause but I changed back to conventional oil and the leak continued. Oil appears on the bottom of the bell housing and will pool under transmission and run to the front of the bilge. My guess is rear main seal but I guess it could be oil pan gasket too...not sure how to tell without pulling apart.

Edited by drh
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take a close look at the plumbing for the oil pressure sending switches.

a small leak there can wander to the bottom of the bell housing.

it can be very hard to see this leak location.

i cleaned the area up really good then wrapped in tp while diagnosing.

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Clean the bilge well, then put down some white absorbent towels under the area in question. Will better isolate where the actual drip is, and can tell if it's tranny fluid vs motor oil

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Good call guys, I hear what you are saying... I'd hate to have to pull the tranny only to have it be something simpler.  I didn't notice anything around the oil pressure switches but the block has always been a bit oily around the back of the block, it's just never leaked to this degree.

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@solorex:  Before you cleaned up the mess, was it simply oil in the center of the bilge or was it a light smear on the starboard side near the bellhousing?  If the latter, that would point you towards the rear main or the trans input shaft seal as a leak in that area would be influenced by the windage of the flywheel, which would simply confirm you latest concern although not pinpointing it to the specific item.  Rear main seal leak is certainly not uncommon (unfortunately).  Pulling the starter and/or the top plug and looking inside the bellhousing may provide some clues.

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It was a new stream of oil that seems to have originated from the center of the bellhousing and there was a stream heading towards the center drain (the low point).  It looked dead center underneath.  But might have been running down the side and then off.  Good idea on pulling the starter.

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Ironically, I also have developed a bit of a leak at the back end of the engine.  Seeing more the comments got me to thinking a bit as that seems a bit high or out of the ordinary.  Talking to one of my OE powertrain engineers he noted that many synthetic oils are now formulated from natural gas.  Not sure there is any correlation, but anytime something changes, there are unintended consequences, just as in the early days of synthetic oils with gasket issues, maybe a similar thing is happening to engines with some mileage on them.  Small leaks in a boat are much more visible or annoying than on an old car that simply drips on the floor like a proper old British sports car.

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Yeah good point.  However I have been using Rotella straight 40 weight since I have owned the boat.  Never used anything else, so I haven't changed anything.

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  • 6 months later...

Ok so back on this topic, boat is out of storage now.  I ordered up new valve cover grommets (PCV) and valve cover gaskets.  Pulled the valve covers and the original gaskets look just fine... still nice and supple (they are the mercruiser factory orange ones).  I wiped down and re-installed for now.  The valve cover grommets were definitely weeping... can they alone cause a serious leak?  I pulled the top rubber plug on the bell housing, looked at the flywheel it appears to be dry... 

There's also oil around the intake manifold, gaskets/bolts.  Is this a common area to leak?  I didn't think there was pressurized oil there, but perhaps in the valleys?

Just trying to trace everything I can before I have to pull the engine for a rear main seal.  There is no oil around the oil pan gasket area either... so I don't think that's it.  It only appears to leak when running.

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@solorex:  with the tilt of the engine, the rear cork intake manifold gasket can be a culprit.  Also, in a different thread, a crew member noted that the oil pressure warning switch tube had cracked, the one at the rear of the intake manifold.

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  • 2 weeks later...

Cleaned the bilge completely last night, there was definitely oil in the bilge from last season, just a film of it but it worked itself all the way back to the rudder.  Fired it up and let it run in my driveway for a good 15-20mins, it got up to operating temperature.  Not a drop of oil that I could tell.  Peaked in the flywheel inspection hole, no oil in there either.  So the only thing I've really replaced are the valve cover grommets.  Kinda scratching my head now.  Guess it's time to put her in the water and see if anything comes up.  But for now I really don't see any leaks.  Oil pan is dry, intake manifold is dry, I spent the whole time going around the engine with a flashlight trying to find something.  Can the PCV grommets really leak that much? 

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@solorex:  PCV grommets and valve cover gaskets can leak enough to form that fine layer of oil in the bilge, does not take much to make a mess if there is some windage in the bilge.  The oil will get quite a bit warmer when you run at speed so that may be the trick to uncover the leak again.  Oil temp at idle stays pretty low.

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