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"Fried" Lower Unit on Yamaha 250

Old 01-10-2019, 08:11 AM
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Default "Fried" Lower Unit on Yamaha 250

Good morning all. I'm writing after receiving some rather unpleasant news yesterday, and was hoping to get some insight from the forum as my mechanical knowledge of larger outboards is limited. I have a Yamaha certified mechanic that's been working on my boat for the past few years. He's always done pretty good work, and seems relatively trustworthy. A few months ago we had a temperature alarm go off just as we were taking the boat out of the water. He looked at the outboard, dropped the lower unit, and said there was an issue when the motor was last serviced--he pointed out a problem with one of the seals and said that may have kept water from circulating properly through the lower unit which would have caused the alarm. He took the lower unit, replaced the impeller and the suspect seal, and put it back on the outboard. I was out on the water the following weekend and the trip was uneventful, no problems. Next trip out a couple weeks later was mostly uneventful, but long story short a seal apparently failed which caused the oil to leak out of the lower unit and the lower unit to then burn up on the ride back in. It now needs to be replaced. I bought a boat with a regular yamaha outboard on it because of what I understood to be a good track record for reliability, and I'm having a hard time figuring out what could have caused the lower unit to fail. But for this incident, the motor has run smoothly since I bought the boat in 2014, has been serviced regularly, and has less than 400 hours on it. Is it possible that something happened during the impeller/seal replacement that could have caused the problem? Is it even possible to identify the cause of the seal failure? Any information during this difficult time would be greatly appreciated.
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Old 01-10-2019, 08:48 AM
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When a lower unit is pulled and the impeller / seal replaced , you would expect that all seals were checked. If the same seal went again , maybe there is a further issue that should have been caught / addressed the first time it was replaced. Stuff happens but something doesn't seem right.

What did the mechanic say caused the seal to fail a second time ?
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Old 01-10-2019, 09:08 AM
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I wouldn't blame Yamaha. Shit happens. Seals go bad. The majority of us have to trust that trained eyes will catch problems, and understand that some problems are not foreseeable. Every outboard lower unit requires oil and seals to keep that oil in and water out. Until sensors are put into lower units to detect fluid issues ($, if even possible), we will have to operate on a bit of trust on the water. The G2 gives you a sight glass in the cowling, but I don't expect people to be popping cowlings before hammering the throttle just to make sure they still have quality gear oil. In summation, shit happens to lower units. It is part of boating. It is not brand specific.
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Old 01-10-2019, 09:09 AM
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Originally Posted by GulfG8r View Post
Good morning all. I'm writing after receiving some rather unpleasant news yesterday, and was hoping to get some insight from the forum as my mechanical knowledge of larger outboards is limited. I have a Yamaha certified mechanic that's been working on my boat for the past few years. He's always done pretty good work, and seems relatively trustworthy. A few months ago we had a temperature alarm go off just as we were taking the boat out of the water. He looked at the outboard, dropped the lower unit, and said there was an issue when the motor was last serviced--he pointed out a problem with one of the seals and said that may have kept water from circulating properly through the lower unit which would have caused the alarm. He took the lower unit, replaced the impeller and the suspect seal, and put it back on the outboard. I was out on the water the following weekend and the trip was uneventful, no problems. Next trip out a couple weeks later was mostly uneventful, but long story short a seal apparently failed which caused the oil to leak out of the lower unit and the lower unit to then burn up on the ride back in. It now needs to be replaced. I bought a boat with a regular yamaha outboard on it because of what I understood to be a good track record for reliability, and I'm having a hard time figuring out what could have caused the lower unit to fail. But for this incident, the motor has run smoothly since I bought the boat in 2014, has been serviced regularly, and has less than 400 hours on it. Is it possible that something happened during the impeller/seal replacement that could have caused the problem? Is it even possible to identify the cause of the seal failure? Any information during this difficult time would be greatly appreciated.
What props are being run on the boat?
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Old 01-10-2019, 09:21 AM
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Originally Posted by yammi250 View Post
When a lower unit is pulled and the impeller / seal replaced , you would expect that all seals were checked. If the same seal went again , maybe there is a further issue that should have been caught / addressed the first time it was replaced. Stuff happens but something doesn't seem right.

What did the mechanic say caused the seal to fail a second time ?
I would not expect that at all.

What specific F250 model are we talking about? What seal are we talking about? What kind of a test are you referring to? A visual test, a pressure test or ???

There are upper seals and lower seals. An upper seal failure might let water in but won't typically let oil out. A lower oil seal failure can allow the oil to depart the gear case. Which seems to be the OP situation. I think.

I would not suspect that any seal that affects the ability of the pump to do its job is one of the oil seals. But, without knowing what seal went bad we are kinda in the dark. Typical here on THT.
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Old 01-10-2019, 10:25 AM
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What year motor?

Saltwater dries out rubber and it fails, part of ownership.
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Old 01-10-2019, 10:27 AM
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Originally Posted by alloyboy View Post
I would not expect that at all.

What specific F250 model are we talking about? What seal are we talking about? What kind of a test are you referring to? A visual test, a pressure test or ???

There are upper seals and lower seals. An upper seal failure might let water in but won't typically let oil out. A lower oil seal failure can allow the oil to depart the gear case. Which seems to be the OP situation. I think.

I would not suspect that any seal that affects the ability of the pump to do its job is one of the oil seals. But, without knowing what seal went bad we are kinda in the dark. Typical here on THT.

I guess we just have different expectations. Maybe I'm naive but if I was working on a lower unit for one problem I would certainly look at the whole thing to see if there were other problems that might pop up and embarrass me (kind of like this) with the customer. The very least would be to pressure test it...maybe the latest problem and big $$ layout could have been prevented. You really don't think that this is a reasonable expectation?
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Old 01-10-2019, 10:30 AM
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Originally Posted by alloyboy View Post
Typical here on THT.
My apologies, as I mentioned in my original post, I'm probably not savvy enough to give you guys all the information you would need. The outboard is a 2008 F250TXR. From what I was told, the seal that failed was one of the seals that keeps oil in the gear case, and water out. Was not offered any explanation as to why the seal may have failed, "maybe" fishing line around the prop but the prop hasn't yet been removed and I don't think there's line wrapped around it.
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Old 01-10-2019, 10:35 AM
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Originally Posted by GulfG8r View Post
My apologies, as I mentioned in my original post, I'm probably not savvy enough to give you guys all the information you would need. The outboard is a 2008 F250TXR. From what I was told, the seal that failed was one of the seals that keeps oil in the gear case, and water out. Was not offered any explanation as to why the seal may have failed, "maybe" fishing line around the prop but the prop hasn't yet been removed and I don't think there's line wrapped around it.
Usually that is the top gear case seal under the impeller. it happens when the boat is stored water corrodes the spring in the seal used to hold tension on the driveshaft.

If the prop shaft seal, fishing braid or a slightly bent prop shaft can do the same.

Good news is after a total rebuild/re-seal you should be good for another 10+ years!

Sam Warner is the gear case king if you are in the Tampa Bay area.
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Old 01-10-2019, 10:37 AM
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Originally Posted by GulfG8r View Post
Good morning all. I'm writing after receiving some rather unpleasant news yesterday, and was hoping to get some insight from the forum as my mechanical knowledge of larger outboards is limited. I have a Yamaha certified mechanic that's been working on my boat for the past few years. He's always done pretty good work, and seems relatively trustworthy. A few months ago we had a temperature alarm go off just as we were taking the boat out of the water. He looked at the outboard, dropped the lower unit, and said there was an issue when the motor was last serviced--he pointed out a problem with one of the seals and said that may have kept water from circulating properly through the lower unit which would have caused the alarm. He took the lower unit, replaced the impeller and the suspect seal, and put it back on the outboard. I was out on the water the following weekend and the trip was uneventful, no problems. Next trip out a couple weeks later was mostly uneventful, but long story short a seal apparently failed which caused the oil to leak out of the lower unit and the lower unit to then burn up on the ride back in. It now needs to be replaced. I bought a boat with a regular yamaha outboard on it because of what I understood to be a good track record for reliability, and I'm having a hard time figuring out what could have caused the lower unit to fail. But for this incident, the motor has run smoothly since I bought the boat in 2014, has been serviced regularly, and has less than 400 hours on it. Is it possible that something happened during the impeller/seal replacement that could have caused the problem? Is it even possible to identify the cause of the seal failure? Any information during this difficult time would be greatly appreciated.
The description and explanation is bit squirly.
Sounds like the engine ran fine, then as was getting hauled, overheat alarm went off. Who last serviced the engine?
Why would he immediately drop the lower looking for an overhead alarm and what seal would prevent the water from circulating?

Originally Posted by yammi250 View Post
I guess we just have different expectations. Maybe I'm naive but if I was working on a lower unit for one problem I would certainly look at the whole thing to see if there were other problems that might pop up and embarrass me (kind of like this) with the customer. The very least would be to pressure test it...maybe the latest problem and big $$ layout could have been prevented. You really don't think that this is a reasonable expectation?
With that being said, he did a water pump and "seal" at this point not checking the lube oil I assume, A) He should have, B) He didn't, so why would he pressure test?
We need more info.
What seal stopped the water from circulating, why and what seal was replaced?
Then we can discuss pressure testing, checking lube condition, etc.
PS: As was asked, what model F250 are we discussing?
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Old 01-10-2019, 11:22 AM
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Between Ole Parker and Alloyboy you've got some pretty sharp Yamaha guys on this one.

I guess I'm having trouble making a connection between the overheat alarm and the loss of gear lube. If the impeller failed an adequate amount of cooling water would not be reaching the powerhead. This would certainly trigger the overheat alarm and cause damage to the powerhead but would not, IMO, cause a loss of gear lube. I had a pair of 2006 F250's and a tube in the lower unit corroded resulting in a loss of cooling water to the prop damper. The prop shaft seal failed and the LU was destroyed but I never experienced an overheat alarm. Plenty of abnormal screeching but no alarm. I'm attaching a picture of the cooling tube that failed, in both of my motors. That tube was eventually upgraded by Yamaha to a SS tube.
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Old 01-10-2019, 02:24 PM
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Don't beat yourself up. It's a 10 year old motor. Go buy yourself another lower unit and enjoy your boat.
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