Hi All! First timer here... Trying to narrow down my problem

[Stimulus-Plan]

First of all let me say thank you to all that have contributed to a GREAT site... I have spent hours reading posts and have learned a lot along the way!

Well, Our second boat and love it but we all know used boats need attention so here goes my symptoms.

1990 270 Thompson Daytona w/twin 4.3 mercs...

Engines are a bit tired. compression averages 100 psi +/- 5%. need to do a leak down test to see if rings or in the heads. Hoping heads Should have squirted a bit of oil in the cylinder while doing the compression test huh?

Need to run 3800 RPM's to hold a good plane, with light load, and only doing around 24mph with 4 blade aluminum props. I never checked the pitch when I bought it. Usually jumps on plane quickly. I think if I step up the pitch it will be to much work on the motors to get on plane.

Jumped on throttle last weekend out of the hole and starboard engine went past 5000rpm's while port stayed around 4400. The weekend before we went out late at night and was running around 4000rpm's on plane with 4 people and gear. Starboard engine got a bit hot. Thinking impeller. Noticed a burnt rubber smell when we beached so I'm guessing my engine coupler(starboard side) is slipping . Would have thought prop hub if no smell... got to the island and let it cool for about an hour. started it up and idled up around 1200-1300 and temp pulled right back down. Could be water pump/clogged risers, etc. but where I dock is shallow and believe I'm sucking a lot of sand and it is eating the impellers up. Overheating that night may have been due to an impeller vane/piece lodged in the water passage way. On the way back to the slip I was easy on it and ran fine. Didn't seem to slip but I babied it. At low idle though temp likes to climb slowly.

Ok, so from what I have described so far, What course of action do you guys recommend? I'm a backyard mechanic and have re-built 6 or so engines in cars and trucks. A few differences in marine engines but I will tackle that this winter. Still hoping heads though Taking her out of the water will cost me $100 alone so trying to get around that. I hope the impellers last the rest of this season or it will have to come out.

So should I just take it easy on her or start troubleshooting some certain areas now? Sorry about rambling on but trying to give as much insight as possible.

Appreciate any advice you guys/gals can offer.

 

[Blk-n-Blu]

Re: Hi All! First timer here... Trying to narrow down my problem

You might want to start with the prop on the over-rev motor draw a line across the prop hub with a grease pencil or a white nailpolish and let it dry and take it for a run, If the line moves you know the prop hub is slipping. Couplers usually go all at once.

 

[Stimulus-Plan]

Re: Hi All! First timer here... Trying to narrow down my problem

Yeah, I read that on here somewhere. I will do that Saturday when we go out again. Probably should pick up a spare hub while I'm at it. That would be a nice and easy fix. Fingers crossed

Thanks

 

[CapnMorgan]

Re: Hi All! First timer here... Trying to narrow down my problem

temps climbing at idle point to the raw water pump/outdrive impeller. Rubber smell may have been exhaust bellows/couplers getting hot due to the lack of water or a sticking t-stat.( I had that problem).

 

[Stimulus-Plan]

Re: Hi All! First timer here... Trying to narrow down my problem

Never thought about the exhaust bellows. Good point! T-stats are cheap. I should just replace them so I can exclude them as a cause. I'll check Bellows for any weakness.

Getting some great input...

Thanks

 

[CheapboatKev]

Re: Hi All! First timer here... Trying to narrow down my problem

Never thought about the exhaust bellows. Good point! T-stats are cheap. I should just replace them so I can exclude them as a cause. I'll check Bellows for any weakness.

Getting some great input...

Thanks

I would think that for the bellows to get hot enough to give you that "rubber smell"..It would point directly to lack of water to cool..lack of water points me to impeller..

But hey...I have been wrong b4..

 

[Bondo]

Re: Hi All! First timer here... Trying to narrow down my problem

lack of water points me to impeller..

Ayuh,... I Agree....

 

[Stimulus-Plan]

Re: Hi All! First timer here... Trying to narrow down my problem

Pretty convinced the impeller(s) is/are bad because of low idle temp climb. The overheating at 4000rpm must have been a blockage. But is it a chunk of the impeller or is it a T-stat sticking? That's why I will just replace the stat(s) to rule it out. Pretty easy and fairly cheap. The guy I bought it from told me the impellers were new last year but you never know... The only other thing I can think of that would cause this is the engine water pump which usually just fails nearly completely(on cars anyway) or maybe,,, Riser blockage...??? I need a good service manual because I'm thinking there are some sort of flappers in the riser/exhaust manifold area. Seems like I read that somewhere before. Anyone know?