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Drive Lube leak in bilge??

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Final update on the oil leak into the bilge. Removed lower unit only to find the shaft bellows with about 2 inches of lube inside. At this point I knew the Lube Monitor Fitting wasnt the problem. Called a mechanic friend to come take a look and long story short, the Yoke seal had torn nearly half way around. After taking a closer look the seal was scored and had heat marks on the side in the same area the rubber part was torn. No grooves on the yoke shaft but there was evidence that the seal had made contact with some of the back portion of the yoke? I was able to get a new seal from the local SR Dealer and finished reassembly about 6:30 Friday evening. Had it out of the lake Saturday and Sunday with no evidence of leaks, just alot of lube still in my bilge...

Not concerned about pulling the lower unit anymore although the B3 is one heavy beast!

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On 7/31/2012 at 7:15 AM, Shepherd said:

Hard to say, but it almost sounds like residual oil from the time before that is leaking into the boat. Adding gear oil to the reservoir after the gear oil is changed is normal if the drive was filled from the bottom plug to the top plug, and then gear oil was added to the reservoir by the tech. Reservoir should stop needing gear oil though after being topped up once or twice.

However,if you get the leak when the boat is driven hard for over 10 minutes, then I would say you have a problem.

If such is the case, I would think the double bearing by the yoke seal was torqued up too much, or perhaps the bearing wasn't broken in properly. Both of these scenarios would allow the gear oil to be overheated, and then have the gear oil leak out by the yoke, into the U-Joint bellows, and then when full enough, the oil leaks down the inside of the boat. Take a careful look at the reservoir, and see if the gear oil level rises after 10-15 minutes or hard driving - say 3800 RPM+

Found this thread looking for a solution to my Bravo 3 oil in bilge problem. I have oil in the bilge but the shop is unable to find the problem. Here's what's happened so far.

1) The reservoir tank emptied into the bilge multiple times.

2) The thru-transom fitting was broken and replaced by a shop (lots of labor!). Bilge cleaned out

3) Boat sat all winter. Reservoir remained full. No sign of a leak.

4) Moved the boat about 1/4 mile in May to wash it in prep for 2017 boating season. Did not start it. Boat parked back in the storage slip. On week later, the reservoir is empty and there is oil on the ground from the bilge drain plug. Clearly not leaking from the sterndrive itself. It's dripping from the bilge drain.

5)  Back to the shop for re-work. Hose clamp at transom fitting and hose to reservoir is dry. Reservoir holds fluid with no sign of leaking. 

6) Shop finds everything dry. Pressure tested the sterndrive. No issues. Removed sterndrive, U-joint bellows is bone dry. No indication of leaks around any seals.

7) Shop changed the high performance lube. Noticed the upper vent plug was under pressure when removed (strange). Boat returned without finding the leak.

8) Last in water use, the reservoir was down slightly (3/8" maybe), which was not surprising since the gear oil was changed. Top off is common. i purposely did not top it off to see what happened to the oil level with the boat in use. After a 10 minute cruise, the oil level was up slightly above full. I released the reservoir cap and heard very slight pressure release. I will replace the cap but doubt that is the problem. After about 2 hours of running, the oil level was down to the ADD mark. This was with the oil hot since it had only been out of the water about 30 minutes. When it cools, I suspect it will go down further yet.  Bilge has oil in it. No sign of a drip.

Any suggestions? Thanks for any help.

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I changed my cap to one that didn't have a relief valve on top.  Solved the problem of drive oil leaking.  

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Any other comments on the “cap” solution.  I just bought a used 2016 Sunesta 224 and am having issues with drive lube in the bilge.  Looks to be leaking around the reservoir cap.  Worried if I remove the vent it could solve the issue but just mask a larger issue that’s building pressure that shouldn’t be there???

Unfortunately the boat was a repo and I purchased from the bank so can’t quiz the former owner ;)

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Also @Jjlai724 do you happen to recall where you sourced an unvented reservoir cap?  I was thinking about replacing the o- ring seal with a round disc (old bike tire cut yo size?) to not have duct tape on the top of the cap!!! ;) 

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39 minutes ago, Buckeye94 said:

Also @Jjlai724 do you happen to recall where you sourced an unvented reservoir cap?  I was thinking about replacing the o- ring seal with a round disc (old bike tire cut yo size?) to not have duct tape on the top of the cap!!! ;) 

The cap is designed to seal while under pressure and vent when a vacuum occurs. Theory is, it will keep the lube side pressurized while underway, helping to prevent sea water infiltration at the prop shaft seal, and also relieve any vacuum that occurs every time a hot drive gets quenched, like when coming off of plane, so that drive does not promote sucking in of sea water. If oil is getting in the bilge, I would look closely at the bottle bottom fitting o-ring and the hose back to the transom plate. The OP may even have a front seal leak where the driveshaft enters the upper gear housing. I would not seal the lube cap off as then it could allow the drive to operate under a vacuum, never a good thing. If yu are experencing an over-pressure condition, then likely you have a trapped air bubble in the drive due to improper venting during re-fill. W

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Thanks @Wingnut   One follow up question- the cap appears to just have a simple rubber washer to seal tight against the bottle threads and a hole drilled in the middle of the cap.  Understand the vent at vacuum, but how would this design also seal under pressure?  Maybe I am missing a flap inside the cap?

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19 minutes ago, Buckeye94 said:

Thanks @Wingnut   One follow up question- the cap appears to just have a simple rubber washer to seal tight against the bottle threads and a hole drilled in the middle of the cap.  Understand the vent at vacuum, but how would this design also seal under pressure?  Maybe I am missing a flap inside the cap?

Think I just answered my own question.  Looked up the reservoir cap p/n and see a small orange disc with a little nub poking through the cap top hole.  Totally was missing this piece.  Problem solved!!!

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9 hours ago, Buckeye94 said:

Think I just answered my own question.  Looked up the reservoir cap p/n and see a small orange disc with a little nub poking through the cap top hole.  Totally was missing this piece.  Problem solved!!!

Yep, that's the check valve. Super simple design, but it works. W

I wanted to take a minute to comment on oil usage in both the Alpha's and Bravo drives as it seems to be a topic that surfaces on the forum almost weekly. My contentions based on 35 years in the Lubes business and over 40 years in boating are as follows.

            First of all, I feel that any actual consumption of oil by a drive system indicates a leak. If the drive shaft bellows accumulates gear oil, the input shaft seal is leaking and needs to be changed along with a careful inspection of the top bevel gear bearing set. If the owner is very aggressive about greasing the gimbal bearing, then it would be normal to see a small amount of carrier oil separation from the grease accumulate in the bellows, but it would not be the same color as the gear oil.

            Secondly, the remaining three drive seals are all below the water line during operation and a leak would be evident by an oil sheen in the water both during operation and at rest. For obvious reasons, these also need to be fixed in a hurry due to pollution issues and also their ability to draw water into the drive housing during cool down. Other than that, there are a few gaskets and an o-ring which I have never seen fail unless they were installed improperly.

            This leads us to the question of "why does my drive use oil, and where does it go?" Based on my experience I suggest the following.

            Gear oil is a complex hydrocarbon matrix comprised of large chain molecules which are subject to a phenomena known as shear. Think of a gallon bucket full of tennis balls. You can only get so many balls in the bucket due to the amount of air that is surrounding each ball. Under heavy loads like water sports as you suggested, some of these molecules break down into smaller pieces due to shear. Now the bucked seems to be only 7/8 full as the tennis balls are now smaller in size, but there are more in number and if we were to weigh the bucket we would find that it weighs the same as before. We did not loose any balls, that just take up less space then they did before. The same thing happens with gear oil. As the molecules shear, they take up less space and it appears that there has been an external loss of oil. Actually it is still there, just degraded in quality somewhat. After 50 to 100 hours of this abuse, it begins to loose its effectiveness and is in need of a change out.

            Gear oils have a very high density, and a fairy low gravity. Drop a golf ball in a bucket of gear oil and it take a while to reach the bottom. Drop the same ball in Gasoline and it sinks quickly. Now weigh each bucket and you will find that the gasoline is much heavier then the gear oil. Gasoline has a higher gravity, but lower density. That’s because its individual molecules are very small with little space for air between them. The same volume of gear oil has a lesser mass as the complex chain molecules are large by comparison and have a great deal of air between them. Beat those big molecules into little ones in a high speed, non-hypoid gear case such as an out drive, and pretty soon the same amount of oil takes up less space, and needs a top off. Nothing actually leaked out, the balls just got smaller.

            Lastly I'd like to suggest a variation in the method in which you and others change your drive oil. I keep reading about the air that gets trapped during refill and the subsequent need for topping off, and also about drive oil reservoir level alarms after servicing, and I can tell you I have a quick and easy solution. DON'T REMOVE THE TOP VENT PLUG, or install it tight prior to refill. When draining the drive, remove the cap from the remote reservoir, and remove the bottom drain plug. It's important to drain the reservoir anyway as sediment accumulates in the bottom of the bottle due to thermal capillary circulation during normal operation. Get this old oil out with the rest of the drive oil as it is just as old and just as worn out. Attach your filler to the bottom drain as normal, and pump up the drive until oil appears in the remote reservoir. Look Mom, no air. The oil tube that runs up to the plastic bottle on the Gen II's exits the drive higher then the top vent plug, thus displacing the mystery air bubble. Using this methodology, I have never had to top off a drive after servicing. If you beat up an Alpha, expect to add a little oil due to shear, but if you are doing that often and there is no external leakage, the drive oil is shot and you need to think about changing it more often anyway. I use a pressure tank to fill my Bravo III-X as it take over three quarts. I change it every 50 hours, and have never had to top a drive off because I don't give the oil a chance to begin to shear and I don't start out with an air bubble in the first place. Keep the top plug in and watch out for shear loss and I think your drive will be around for another decade or so. I hate to hear our forum members talking about top off on drives without level alarms. If you have to add a half a quart to a Bravo, or even less to an Alpha, then the top bevel gear set and bearings in the upper gear case are already taking a big hit. Hope this helps.

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