2003 Yamaha OX66 VMax 200 3.1L Overheat Problem

[dontreder]

I know... lots and lots of info out here, and I'm pretty confident I'm on the right track. Like others on the forum, here is my problem...

2003 Yamaha 3.1L VMax 200 2 stroke with about 300 hours, used mostly in salt water, and has an overheat problem at high RPM's - above 4200. Here is what I've done so far:

1. Replaced water pump assembly.
2. Replaced poppet valve, spring, and bushing assembly.
3. Replaced thermostats
4. Tested sensors - they work, and believe the indication is actual.
5. Flushed whole system with RidLyme

So - I think I'm at the point of pulling the heads for a good visual inspection and cleaning. But, before I do so, wanted to put this out to the forum for a final call for advice before going to step 6. Specifically, if I do pull the heads, I saw one thread about coating with some type of paint? Want to know more about that or similar options before going further. I'm very good with tools and have all things needed to do the job correctly... no issues there.

Other than this, motor is in excellent condition and runs perfectly.

Thanks in advance... appreciate everyone's help and advice on this!


PR

[pstephens46]

Are you the original owner? If not, how
many hours have you put on it?

[dontreder]

No, not the original owner, but have had it for over a year myself. The boat has had 3 owners in total, from what I understand.

Regarding hours, the hour meter said 276 when I bought it and is now says 306.

Thanks

PR

[TownsendsFJR1300]

Zinc Chromate is what you want to use on bare aluminum (say scratched internal water passages):

https://www.amazon.com/MOELLER-MFG-C...r+for+aluminum


Your engine does have very low hours but is still 13-14 years old and you don't know if the PO's flushed it, etc.

How corroded were the thermostats, salt build up in the block that you could see?

In any case, even with the Rydlyme flush, if it's clogged up bad, the solution can't get thru and can only do so much...

*As a side note, my neighbor's 200HP, 2 stroke had the overheat issue EXACTLY as you do. Did the WP, etc.

We eventually pulled the heads. Probably 90% of the lower water jacket was caked shut with salt. The heads were also full of salt, caked up... Picking at it with a screwdriver was the only way to remove it (maybe bead blasting).

Once that was cleaned and assembled, the engine ran great. No more overheat alarms and the engine tached out normally..

[dontreder]

The thermostats were moderately corroded, and so I replaced them. Passages were visibly clean with very little corrosion visible after treatment w/ Rydlyme. Even before the treatment they weren't that bad.

That said, looks like my next step is to pull the heads...

Appreciate the help.

PR