Going through prop shaft seals

[MN Basser]

2008 250hp ProXS Serial Number 1B585330

Hoping someone can point me in the right direction with somewhat frequent lower unit seal failures. I'm in Minnesota, so the boat/engine gets winterized and goes into storage in November and comes back out usually April - May timeframe.

• In August 2015, the lower unit was replaced after I apparently hit something and blew apart the gears. Tag on the new LU says +G/HSG ASY 1.75 XL, TM, SILVER.
• During winterization in November 2018, dealer found fishing line wrapped around the prop shaft and so they "resealed LU".
• No issues in 2019 and had boat winterized by same in dealer in Nov. 2019.
• May 2020, I found the LU leaking around the prop shaft and found the inner seal had partially pushed out. This was after using the boat 2 - 3 times at the start of the open water season. I took the boat back to the dealer. They replaced the prop shaft seals and said it was probably from fishing line even though there was nothing wrapped around the prop shaft.
• July 2021, I found LU leaking again with inner seal pushed out. Brought it in and they simply replaced the seals again.
• June 2022, same thing - I found the LU leaking again with inner seal pushed out. Upon bringing it in, I provided the history to the dealer and asked that they figure out what's causing these seals to push out. They said the only thing they could find was that bearing carrier (which holds the inner seal) was slightly out of spec, so they replaced that and replaced all seals including the top.
• October 2022, same thing again. I find the LU leaking and can see the inner seal pushed out. So its back to the dealer. I called late last week and the tech said he's been trying to work with Mercury tech support to determine what the issue is.

This dealer is a widely known dealer in Minnesota with 4 locations. I never had any problems with them for other service work either on my engine or boat. They are performing a pressure test whenever they do work on the LU (at least that is what the paperwork says).

I usually have the boat out 1 - 2 times per week from early May to late October. Most of the lakes I fish are relatively small, so for me to be running on plane more than a few minutes is rare.

I'm planning to keep the boat another 1 - 2 years, so I would really like to get this issue figured out so I don't have to replace seals once or twice per summer. And so the new owner doesn't have to deal with this issue either.

Has anybody ever run into something similar? Any ideas as to what is causing this?

Thanks in advance,

MN Basser (Jon)

[EuropeanAM]

Likely either:

1. Seal getting knifed/cut during installation of bearing carrier (even seen this from the factory on a few occasions)

2. Seal not seated to correct depth with proper seal installer

3. Gearcase being over-filled (no expansion room). This gearcase needs to be 1-2 oz BELOW the bottom of the vent hole. Especially likely where it's filled in COLD temps and then launched/run in WARM temps.

[lpugh]

and be sure there is no water still in the case after seal replacement, I replace the gear lube after one trip out if the case has a lot of water in the oil as it clings to surfaces very well and will not completey drain out. Can cause the same isues as a overfilled case due to expansion. Does not take much water to cause this

[blackboat]

I clamp a heat lamp next to the LU and let it drain for a day.Not close enough to get super hot but pretty warm to the touch.Fairly sure most if not all the water is gone.You might try red Loctite on the seal circumference if all else fails.Is Mercury installation tool 31108 correct?

[lpugh]

^^^^^^ That works quite well is you can wait that long to finish the job

[EuropeanAM]

You might try red Loctite on the seal circumference if all else fails.Is Mercury installation tool 31108 correct?

Red liquid loctite on outside circumference where seal OD is METAL. Clean surfaces of carrier with appropriate solvent first.

Installation tool for the seals in the G1 TM is 817569T.

[MN Basser]

Thank you all for the replies.

The dealer called me yesterday afternoon with an update. A Mercury service manager was there yesterday looking at my engine. Merc has seen this issue before, but it has been on high speed boats that make long runs typically down in the Gulf area. And in those cases, they see heat damage around the bearing carrier and prop shaft seals (like the rubber is melted). The LU heats up melting the seals and eventually pushes the inner seal out with the pressure build-up. I told them it is rare that I run on plane for more than a couple minutes at a time. They do see a little heat build up by the water pump, but that is fairly normal. Otherwise, there is no evidence of excessive heat in the LU. All the internal parts look good, and the LU lube still looks fine and doesn’t smell burnt. I’m actually not even getting any water into the LU. But once the seal goes, I start to leak fluid out. However, the outer seal is still intact, so water is not allowed in.

They are baffled, but did give me two options.

1. There is a water strainer below the powerhead that filters waters going out with the exhaust through prop (it is meant to keep that exhaust path cooler). To check if that strainer is partially clogged, though, they would have to remove the powerhead, which would be several hours of work. And they really don’t think that is the issue because they don’t see evidence of excessive heat build up anywhere in the exhaust path. (Hopefully I explained that correctly).
2. Run high temp Mercury racing gear lube in my LU.

I told them option 2. They are going to replace all seals and the water pump, then fill the LU with the racing gear lube.

So we’ll see how this goes next summer….

[wmitch2]

Could a bent Prop Shaft cause this ??

[EuropeanAM]

Possibly... surely that would have been checked.

I concur that it's probably not the exhaust strainer. Not sure I'm biting at the lube making that much difference (the High-Performance should be very well in that gearcase).

[MN Basser]

The 'racing' gear lube they used is Mercury Part Number 82-8M0111677.

Mercury-Quicksilver 92-8M0111677 SAE 85W90 Extreme Performance Gear Oil

@Don - are you saying this is what they should have been using all along?

I looked back through my service records. "Bulk Gear Lube" has been used every year including when the LU was replaced. The part number for that is generic or at least dealer specific (i.e. part number 1230).

[EuropeanAM]

It is acceptable to use the Racing/Extreme Performance lube. Not necessary, but acceptable.

Spec called for "High Performance Gear Lube" (Mercury or Quicksilver). Quite likely that this is what they have in their bulk supply (many shops keep the Racing Lube in smaller quantities that have to be requested for each job).