Finding Leaks in a Boat

Not again…

In my last blog entry (Engine Outdrives: Inspect Those Bellows), I told you about “a friend of mine” who discovered a leak in a little runabout he had just bought. Soon after he fixed the U-joint bellows boot in the stern drive that was cracked from age and use, he took his family out.


In addition to the U-joint bellows boot, the shift cable boot (below and to the right of the gimbal bearing shown here) and the raw-water feed hose (upper left) also should be replaced about every six years. Stay tuned for a blog on corrosion in the gimbal bearing, also visible here.

When I, er, I mean, he opened the doghouse to check on things, he found that he still had a leak, somewhere. But he didn’t have a clue how it could still be leaking. He had fixed the leak by replacing the cracked rubber boot, right?

Well, turns out he had fixed one of the cracked rubber boots. As it turns out, there’s another boot that will spill water into the bilge: The shift cable that runs through the drive has a boot of its own. Although the shift cable boot is completely hidden and not susceptible to possible photo-aging, it can split and allow water in.

Water won’t get into the gimbal bearing unless it gets deep enough in the bilge to seep back in. The factory-recommended service interval for the shift cable boot also is six years. The leak is typically slower, but it’s still a leak and it had to be fixed.

While my friend was fixing the shift cable boot, he saw one last piece of rubber in the drive — the raw-water feed hose. This hose also has a six-year service interval, so he figured he would replace it while he was in there. The parts guy told him those hoses don’t break often, but the inside walls can separate and collapse, which will cause the engine to overheat. It’s rare, but after pulling the drive apart twice, he wasn’t taking any more chances, so he replaced that too.

Next trip out to the lake, he checked under the doghouse again and it was nice and dry. Looks like he finally fixed all the leaks. This time I’m sure. I mean, he’s sure.

Brett Becker


  1. Bruce Rogers says:

    I have a 1998 3L Bayliner Maxum with a alpha-1 generation two outdrive.
    Had a marine mechanic pull the old engine and outdrive and installed a brand spanking new 3 L motor.
    The outdrive was completely taken apart gone through and replaced anything that possibly could have gone wrong in the foreseeable future.
    From day one I was losing Gear oil from the sensor mounted on the motor.
    There is no oil in the bilge or any leaking from the outdrive.
    The motor has 50 break-in hours with a gear oil and motor oil change
    Plus about another 40 hours of run time.
    Once the outdrive is pulled how am I supposed to tell where the oil is leaking??? Or do I just replace all possible O-rings and gaskets that are supposed to keep that gear oil where it supposed to be???
    If oil is leaking inside the outdrive bellows (the large one) can there be only one possibile place to look?
    How does the gear oil travel when it leaves the transom and goes through the outdrive to be able to replenish the volume of gear oil in the drive should I encounter a leak??? Will I be able to see if seals or O-rings are damaged???
    Please provide part numbers for parts I may need and also what type of grease that I may need to re-grease the gimbal bearing and yoke should that be necessary once I’m inside the outdrive???
    What tools may I possibly need should I need to remove some bearings???

    The engine is mounted rock solid in the engine compartment and everything sounds fine when the engine is running.
    Something was wrong with the oil leak from the beginning but I did not know was wrong until too much time had passed so I’m learning the hard way. This is my first outdrive.
    When I remove the outdrive is there a check valve that closes so the outdrive can be pressurized???
    If I cannot just purchase O-rings or gaskets tell me the part numbers for the kit or kits that I need.
    I am pretty mechanically inclined and don’t feel this is beyond my capability.

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