Earlier this summer while on P.K. my engine suddenly started making a loud metal on metal knocking noise.

Engined died as I was coming off plane. Immediately trimmed the motor up and trolled back to the launch.


Was told lower unit needed replaced, so replaced it and had all maintenance done.


I get my boat back and all seems great. Fires right up, runs like a champ. Then when we are ready to leave, I fired her up and she began smoking. Bright blue smoke, unmistakable burning oil. Smokes for a couple secs and then nothing. Figured maybe some oil was spilled during maintenance and didn’t think much off it because it was only for a few secs.

Next club tournament was O.H. Ivie. Fired her up that morning, no smoke. Fish and run around with no issues. Then midday I,m running across the lake doing about 55 mph and she suddenly starts to slow down. WOT and trimmed ou I was doing 48 mph at 5300 Roma where normally I’m doing 57-58 at 5800-590l rpms.

We stop and fish for a while and when we make our next move she smokes horribly. Again it goes away quickly.

Launched it the next day at Lake Coleman and when I started it, she covered the entire parking lot in a cloud of smoke.


Brought her to the shop. They checked compression, all good. The ran leak down tests, results were excellent. Mechanic mentioned the oil looked like no oil he had ever seen and was convinced oil was contaminated with something, but no evidence of water. Oil was over a quart low after only 3-4 hours since previous oil change. Said my bottom 2 spark plugs were heavily fouled, so replaced those. Told me to use boat and we would closely monitor oil consumption, but he didn’t see any issues and couldn’t get it to smaller after starting and stopping several times over 2 weeks. Was hoping good oil made the difference.

Next trip out was another club tourney on Ivie. Was able to run at 57-58 and no smoking through half the day. Then mid day while making a move, I felt her slowly start to lose power. Before I knew it we were struggling to do 50 at WOT. When we came off plane she began smoking. Same symptoms all over again.

Fished Alan Henry yesterday. She smoked several times throughout the day and for the first time I could see her smoking while on plane. She fluctuated from 53 mph and 46mph. When we were returning to launch for weigh in, my low oil alarm went off. Again, 3-4 hours after a 2nd oil change in 2 months.


She is now picked up and not going back on the water. Any ideas on what could possibly be causing it to burn oil?

Undecided on bringing it back to the last mechanic that changed oil and spark plugs after being given the symptoms or putting some fresh eyes on it.

Which oil are you using?

I honestly don’t know. I’ve just trusted those servicing my engine to put what they felt was best since I’m about the furthest thing from a mechanic.

I will say these last 2 oil changes were done by 2 different shops.

You are burning crankcase oil, which is leaking into the cylinders most likely the ones with the fouled plugs. Worn/locked rings, bad valve seal, worn cylinders are the main culprits. Your oil consumption is high, possible the oil seal rings are stuck or worn allowing oil into the cylinder, this could explain your power loss as well.

How many hours do you have on the engine, just curious.

Which HP? Hours on the powerhead? What is the timeframe between the aforementioned outings? When out on the water, are you significantly idling (graphing)? Any fuel trail on the water when it’s misbehaving? Any diagnostic faults? Can you post the last Yamaha Diagnostics report?

Irregardless, I’d suggest you remove the existing oil and ensure replacement with proper Yamalube to eliminate improper oil as a contributing factor. Inspect all plugs and verify they are in spec - proper type and gapped correctly. Recheck compression (different shop) and leak-down and report the specifics for each cylinder. Also have them provide you with a Yamaha diagnostics report...

250 hp, 440 hours

Deans in Odessa changed oil in late September/early October and started it multiple times over a 2 week period, didn’t smoke once.

They changed plugs as well.


The fouled plugs are definitely reason for loss of power. With new plugs I was able to run 57-58 mph for most of the first day I had the boat back on the water. About midday it suddenly started smoking when I cranked it up, and noticed a loss of power.

Fished a tournament on O.H. Ivie in October, fished the Saturday and Sunday. Then fished Alan Henry this past weekend. So 3 days on the water, maybe 3 or 4 total hours, maybe.

Purchased the boat in 2014 from FunNSun as a demo with 36 hours on it.

Thinking of bringing it back to them just have have another set of eyes.

Deans ran Compression and said everything looked good. They then ran leak down tests and said everything was 3-4% so they didn’t feel that rings, seals, or my cylinders were bad.

Oil is getting into the cylinder, fouling the plugs (physical evidence proves this). What I mentioned above are the causes. You can have good compression, a good leak down test and still have a locked oil control ring. The fact that both compression test are good pretty much narrows down that conclusion.

You can tilt motor and soak the effected cylinders in any of these: B-12, Seafoam, ATF, or mineral spirits. Look up the procedures on how to do this if you wanna go this route.

I don’t disagree with Alumacraft14’s suspicion and non-invasive attack. With the issue apparently not isolated to a single cylinder, this diagnosis would imply that at least two cylinders have locked oil control rings. This leads me to believe that they too may also be symptoms and not cause. The mechanic’s comment regarding improper/contaminated oil may be telling.

Give the information that we have, I’m suspicious of an over-oiling misbehavior (break-in)...

Appreciate the info.

I am the farthest thing from a mechanic, so I can only go off what the mechanics have told me.

Was told next step was to tear down block and then was looking at thousands just for the labor to tear down and put back together before any repairs are made.

So anything I can try before committing to spending several thousand, is greatly appreciated!

Is your motor propped to hit 6000 rpms? If its not reaching that then its over propped and can cause issues like this. Usually it causes the oil level to rise with unburnt fuel slipping past the rings but over time will also build up excessive carbon causing the rings to stick. If it is propped correctly dump a can of ring free in there and run the snot out if it for about 30 minutes and by run the snot out of it I mean wide open screaming. Let it cool down then repeat. From there monitor your oil level and see if it gets better.

Yes i am able to hit 6000 rpms easily before plugs foul.

In an effort to avoid a major mechanical, I’d suggest you aggressively attack it with Yamaha’s Ring Free, or whatever product you deem appropriate, as mentioned above. If you’re going to soak cylinders, consider soaking them all in a preemptive effort to avoid chasing this issue on other cylinders in the future...

I agree with these guys. Worst case you have to rebuild, which was your mechanics first option. At least this way you have a chance it fixes it for less than $100. What boat are you running? I have a legend le21 with a 225 and I am running low 70’s with a heavy load. Not bashing, just wondering if your motor may be struggling if a 250 is only pushing 58.

I have a 22’ Skeeter Center Console. Doubt there is any more speed to gain.

That explains it. That is a BIG boat!

Thanks for all the feedback.

I Think this is going to be my plan:

1. Soak Cylinders in Seafoam over the course of 3-5 days.
2. Run Ring Free Shock Treatment with 2 oz Ring Free/gallon fuel (total 6 gals)
3. Change Oil and Filter
4. Change Spark Plugs

Last time I changed my own oil I used Yamalube Fully Synthetic 5W/30. My oil is extremely low right now. Anybody see any issues topping off my reservoir with a cheaper marine oil simply to run the 6 gallon ring free shock treatment since I will change the oil immediately after?

I don’t want to cause damage trying to save $100, but hate to just throw money away as well.

If you ask on certain forums they will tell you that once you do the above and get her back on the water you need to "blow the soot" out of her!

A lot of Yamaha people say the SHO's need to be ran hard (ie High RPM's) to keep it from burning or making oil which is whole 'nother problem.

Hope you get it figured out and it isn't an expensive fix.

Well I hate searching for symptoms seeing others with same symptoms and never see the results.

So tried the soaking/cleaning with sea foam and ringfree slug treatments and it didn’t work.

Brought it to mechanic and had them run their combustion chamber cleaner. For a while it seemed as though it was working. Only smoked when I got it above 5500 rpms. Mechanic said to keep running it at 4500 with the ring free additive and maybe it would free up whatever was sticking, but they didn’t think it was anything major.

Well next tournament never got it above 4500 rpms and it started smoking heavily mid-day.

Took it to a 3rd mechanic. Said he put fresh oil and after 30 mins had water in oil, water on plugs, it was spewing oil out the top and burning way too much oil and smoking.

Said it would likely be cheaper to replace power head than to diagnose everything and repair.
Need a new power head.

Did the mechanic ever do a leak down to see if its power head are if have a bad head.

Leak down and compression checks were good.