High RPM overheating.

[Sheff 69]

I couldn't find the prior threads with the other posts (apparently went away with the upgraded operating system here) but

here's some reading for ya. As most engines nowadays have a flush port on the power head, I don't see why you would have to remove the impeller.
Removing the thermostat is a "should do" for the most effective treatment.

http://www.rydlymemarine.com/assets/...structions.pdf

Thank you.

I went to the web site and thought that looked very interesting. I phoned them up and spoke to one of their Engineers. He told me the product does work well, but is hell on zincs. Either pull the zincs first and plug any holes, or replace them afterwards.

He said pull the T-stat, put the bottom of the motor in a 5 gallon plastic drum, get an old live-well or bilge pump and recirc the liquid through the flush connection for about 30-40 minutes.
Said that should work.

I now have another problem. I have the Yam Service Manual and it does not mention internal zincs - nowhere.
I resorted to the nearly discarded Seloc manual, and it says I have at least one zinc possibly two under the head. Shows a general location for one of them, as indicated by the red arrow.
Does anyone know if this is the zinc, and can it be got at through the T-stat housing? And are there anymore hidden away? This is the 2002 90TLRA motor.

Thanks for the help
John

[rodbolt17]

typically those two zincs are on the block and require cyl head removal for access.
what you will be amazed at is the fact that other than being rather gray they will be intact.good idea, never worked. after about the third drying cycle the anode is covered with a calcium like deposit that renders it simply another part along for the ride. myself I would replace the water pump with the correct kit,replace the T-stat and pressure control valve grommet and pop the head and cover . check the head for flatness,clean the head and block and go boating.
take maybe 3-4 hours if corrosion is not a factor.

[Sheff 69]

typically those two zincs are on the block and require cyl head removal for access.
what you will be amazed at is the fact that other than being rather gray they will be intact.good idea, never worked. after about the third drying cycle the anode is covered with a calcium like deposit that renders it simply another part along for the ride. myself I would replace the water pump with the correct kit,replace the T-stat and pressure control valve grommet and pop the head and cover . check the head for flatness,clean the head and block and go boating.
take maybe 3-4 hours if corrosion is not a factor.

Thank you, I will do that. Presently out of town for the summer, so can't work on engine anymore until September. I will keep the forum informed as to what happens.

Hope y'all have a good summer.

John

[Sheff 69]

Resurrecting this thread to close it out. Back to the boat after the summer.
I pulled the thermostat cover and could see quite a bit of scale, so I pulled the head and cover and the exhaust covers. The photos show what I found. Not quite as bad as I thought, I’ve seen worse in auto engines. Even the marine engine rebuild shop said they’d seen a lot worse. Anyway I had the head and cover bead blasted and painted, and I scraped out the junk in the cylinder water passages and exhaust covers. I didn’t really see any true blockages of any kind.
I checked the T-stat and thermal sensor and they both came within specs so I reused them. I did soak the pressure release valve and T-stat in regular vinegar, and within 30 minutes they came out clean, so there’s hope in using that technique. I tapped out all the threads before rebuilding the engine. I also checked the water pump which was perfect, so since it only had 15 hours on it, I re-used it.
I took the boat out yesterday and ran it for 20 minutes at 5500 rpm with nary a squeak from the alarm.
So I guess it really was the crud build up in the water passages.
Thanks for everyone’s assistance in walking me through this.

John

[panasonic]

Glad it worked out for you.

[Sheff 69]

Resurrecting this thread to try again to close it out, and to provide more information for anyone else experiencing this problem.

Turns out I was too optimistic. Problem resurfaced, not quite as bad as before, but too bad to leave alone.
I finally decided to bite the bullet and pull the powerhead.
I think I finally found out what was causing the problem. When I split the power head from the upper case, I found the gasket material around the exhaust port had totally disintegrated and was allowing the exhaust gases to blow up into the water passages of the heads. I am guessing that at high rpms the exhaust gases were entering heads and
preventing good water flow.
Pic below shows the square portion of the gasket supposedly sealing the exhaust. I never would have thought this as a possibility.

Now it is apart, I've decided to rebuild the power head.

John

Img_1833a.jpg.

[TownsendsFJR1300]

Dam.... Nice to find something wrong with NO DOUBT, is an issue....

Something to make note of for future posters of unknown overheating issues...


.