# Bad noise on my 25 Merc



## jethro (May 5, 2014)

I know this board isn't big for this, but I do a lot of trolling for coldwater fish. My 1995 25 hp Mercury is making a bad noise, mostly while I am idling along just in gear which I obviously do a lot. It will be quiet for a while then it will start making a high pitch squealing noise that will come and go. Recently it seems to be there more than not. It doesn't make this squealing noise when it's under half throttle or more. It also doesn't seem to affect speeds or fuel economy. It sounds to me like it's a bearing of some sort, what kinds of bearings are replaceable in my motor? I know there is one in the lower unit, can I replace it myself? Could it be the water pump? Just trying to get some feedback and thoughts before I tear into it. No way I am bringing it to a dealer. I need to do a new water pump anyway, so I guess I'll start with that,


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## crazymanme2 (May 5, 2014)

Whats your lower unit oil look like?


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## Boat2fast (May 5, 2014)

Does it make the same noise with the cover off? Anything near the flywheel? Anything loose under the flywheel...electrics? First things come to mind...


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## acwd (May 5, 2014)

I had a old 20 hp Merc that started making a howling sound. Just started doing it. It was a supply tube for the upper bearing in the motor. The line was rubber and cracked. I dont know if yours has that line or not. Worth checking.

Steve


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## jethro (May 6, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351331#p351331 said:


> crazymanme2 » 05 May 2014, 17:11[/url]"]Whats your lower unit oil look like?



Lower unit oil looks good, just replaced it. No shavings in there, not foamy, not too dark.


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## jethro (May 6, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351357#p351357 said:


> Boat2fast » 05 May 2014, 21:39[/url]"]Does it make the same noise with the cover off? Anything near the flywheel? Anything loose under the flywheel...electrics? First things come to mind...



Yes, I took the cover off but I still can't tell where the noise comes from.


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## jethro (May 6, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351368#p351368 said:


> acwd » 05 May 2014, 22:59[/url]"]I had a old 20 hp Merc that started making a howling sound. Just started doing it. It was a supply tube for the upper bearing in the motor. The line was rubber and cracked. I dont know if yours has that line or not. Worth checking.
> 
> Steve



What does it supply? Not oil obviously, it's premixed. Water cooling?


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## JMichael (May 6, 2014)

Only thing other than whats been mentioned that I can think of is the recoil starter. I've seen them have issues and start making intermittent squealing sounds.


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## acwd (May 6, 2014)

It supplies fuel mixture to the upper and lower bearings for lubrication I guess. The only thing I could figure it done. It cracked in half and ran the upper bearing dry. Replaced the line with a semi clear fuel line for a chain saw and it quit making the noise and you could see fuel going thru it. One end hooked on a tee in the crank case and the other at a elbow at the upper bearing housing. Had another line running from the tee to the bottom bearing too. 

Steve

Update. The hose is called Bleed Drain hose. It must pull a vacuum on it from the crankcase to pull fuel mixture into the bearings instead supplying fuel mix to them. It goes one way or the other. All I know is it was making a howling noise and I found that line broke replaced it and the noise quit.


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## captdan (May 6, 2014)

Jet, what prop are you using? Is it the stock aluminum prop or a stainless prop? On smaller outboards, sometimes you will hear what we refer to as "driveshaft chatter". This can be heard at lower speeds and usually disappears as you give more throttle. Usually this is evident with a stainless prop.

Before you go tearing anything apart, you need to isolate your issue. Drop the lower unit, hook up the garden hose to the water pickup tube, and run the motor. If the sound still persists, you know the issue is not the lower unit or driveshaft.


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## jethro (May 7, 2014)

Thank you Steve, I will look into that. I looked last night for a minute but didn't see any fuel lines feeding the top of the motor at all. 

Captdan, I am using the stock aluminum prop. The sound is intermittent which is making it hard to troubleshoot. Last night I hooked up the ears (lower unit in place) and ran the motor in the driveway for 5-7 minutes at very slow speed in gear exactly like when I troll. Took off the cowl and waited for noise but no noise happened. Once the tell tail starts getting real warm I don't like to run it on the ears so much, so I shut it down. Tonight I will take it on the water and run it there to see what I can discover. I will take the cowl off while on the water and see if I can at least determine if it's up top or down below.

Thanks everyone for the help, this is a great forum.


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## captdan (May 7, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351522#p351522 said:


> jethro » Today, 08:07[/url]"]Thank you Steve, I will look into that. I looked last night for a minute but didn't see any fuel lines feeding the top of the motor at all.
> 
> Captdan, I am using the stock aluminum prop. The sound is intermittent which is making it hard to troubleshoot. Last night I hooked up the ears (lower unit in place) and ran the motor in the driveway for 5-7 minutes at very slow speed in gear exactly like when I troll. Took off the cowl and waited for noise but no noise happened. Once the tell tail starts getting real warm I don't like to run it on the ears so much, so I shut it down. Tonight I will take it on the water and run it there to see what I can discover. I will take the cowl off while on the water and see if I can at least determine if it's up top or down below.
> 
> Thanks everyone for the help, this is a great forum.




You've got to isolate your components. You would have to remove the lower unit and hook up the hose to the water tube. Don't be afraid of the warm water on the mercs. They feel really hot but that is how they like to run. My 2001 merc is very hot to the touch... I put an infrared thermometer to the water and it reads at 142, right in range where the engine temp should be at idle. 

Are you experiencing the problem only under load or in neutral as well?


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## T Man (May 8, 2014)

Does it almost sound like a belt squeal?


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## jethro (May 8, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351625#p351625 said:


> captdan » 07 May 2014, 22:50[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=351522#p351522 said:
> ...



Well, I can't seem to recreate the problem in my driveway, pain to diagnose that's for sure. Tonight I am going to take it to the lake.


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## jethro (May 8, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351683#p351683 said:


> T Man » 08 May 2014, 12:05[/url]"]Does it almost sound like a belt squeal?



You know, I guess possibly, but it sounds to me more like a dry bearing. But now that you mention it it could sound like a belt.


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## jethro (May 9, 2014)

So last night I was able to recreate the noise while on the water. Some things that might help diagnose... I am almost positive it is on the top end of the motor. When I pulled the cowl off I could hear it better. It seems to only happen when the motor gets warm. And it does happen weather under load or in neutral.



[url=https://www.tinboats.net/forum/viewtopic.php?p=351683#p351683 said:


> T Man » 08 May 2014, 12:05[/url]"]Does it almost sound like a belt squeal?



Yes, it does sound almost like a belt squeal! Any ideas??


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## acwd (May 9, 2014)

Is it electric start?

Steve


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## jethro (May 9, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=351813#p351813 said:


> acwd » 09 May 2014, 12:14[/url]"]Is it electric start?
> 
> Steve



It is an elec. start, any idea what I should look for? The starter gear is disengaging as it should.


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## acwd (May 9, 2014)

pull the flywheel off and check things under there. maybe something came loose. can also check the side play in the upper bearing while your in there.

Steve


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## T Man (May 10, 2014)

jethro said:


> So last night I was able to recreate the noise while on the water. Some things that might help diagnose... I am almost positive it is on the top end of the motor. When I pulled the cowl off I could hear it better. It seems to only happen when the motor gets warm. And it does happen weather under load or in neutral.
> 
> 
> 
> ...



Nope, but I get the same sound from time to time


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## acwd (May 15, 2014)

Any updates on this problem? Just curious.

Steve


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## jethro (May 16, 2014)

Oddly enough, I have been out twice now and not had any indication of the noise. I think I may have used the wrong spec gear oil when I last changed it. When I changed my lower unit oil last I used cheap Pennzoil 80wt gear oil that I got at the local general store. I drained that out and used some good stuff I bought at Bass Pro, Mystik 90wt I believe. Could have sworn the noise was from my top end but you know how noises can travel. Maybe that oil was not the right spec? Anyway, since changing that oil I haven't been able to recreate the sound. When I bought the boat I never changed the gear oil from the original owner and it made that noise too. Probably had the wrong oil in it from the original owner.


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