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Alpha 1 Gen II OutDrive Fluid leak

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I went fishing today, and after I loaded my boat on to the trailer I noticed some blue fluid on the ground.  I checked the drive fluid reservoir in the boat, and as you can see by the pictures below it did not appear to be too low.  This leak just started today because I've never noticed it before.  I called my local marina to determine what the problem could be; however, due to the holiday weekend coming up they cannot look at my boat until after the holiday.

So I did some poking around and took some pictures for you all.

Initial leak seems to be due to a cracked or dry rotted line:


Nothing leaking from the grey plastic elbow that connects the O/D to the bellows (i ran my finger all the way up the elbow and it was dry):


However, as you can see below the leak is coming from the hose that connects to the O/D:


Fluid level of the reservoir after I found the leak:


It's not an extremely fast leak, but the more I examine that line it is definitely dry rotted pretty bad (much like the exhaust bellows).

Since my local marina cannot fix this issue until after the holidays I just wanted to get some input from the community.

Thank you.


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I'm thinking the oil reservoir hose has a small hole in it if you found no oil leaking from the thru-transom fitting. Perhaps the press-in check valve that is in the bell housing is the culprit. Looking at the condition of the shift bellows, I recommend replacing with the following MerCruiser parts: NOTE: cracked or missing exhaust bellows won't leak water into the boat, but a sliced or broken shift or u-joint bellows will.

30-803099T1 - Alpha 1 Gen II transom ,bellows kit (includes u-joint, shift and exhaust bellows, water hose, mounting gasket, gimbal bearing, and oil hose)

865436A03 - Alpha 1 rear shift cable kit (comes with shift bellows and mounting gasket, but only costs a tiny bit more than a 865436A02 which is just the cable)

805320A03 - Alpha/Bravo trim sender kit

The plastic oil reservoir thru-transom fitting is REALLY fragile and breaks easily, but is not very easy to reinstall...also recommend having the shift shaft bushings inspected.

You can continue to drive the boat for the near future, but carefully watch for signs of gear oil consumption. Will of course see some signs of oil seepage in the water.


Image result for mercruiser alpha 1 bellow housing


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Thank you for your insight Shepherd. Yes it is the reservoir fill tube that has the leak.  It's a shame this little hose that I can see is going to cost me so much to get repaired.

According to your recommendations the parts to do a correct service and repair will cost me around $335 USD.  Of course this does not include marina's service fee.

What Mercury specific tools are needed to perform this repair?

Thank you.


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Does the Sierra kit# 18-8206-1  that replaces # 30-803099T1, come with the gear oil hose?  Forgive me I cannot verify with any online site if it does.  Overton's doesn't list all included parts, and every picture I find of the Sierra kit only shows the water hose.


Thank you.


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  • 4 weeks later...

Just wanted to say thank you to everyone that replied to this thread.  I took everyone's suggestions and I replaced the following:

All bellows, water hose, gear lube hose, gaskets, and shift cable.  The only thing I did not replace was the trim sending units.  I cleaned them and mounted them; however, they still need to be adjusted.

This was the first time I've ever attempted something like this, and after 2 successful launches I feel confident that everything is okay.

I am now more confident in my mechanical skills, and I've saved money performing the work on my own.  Plus I've gained the knowledge of how my outdrive is disassembled and reassembled.

Thank you again.


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