Yamaha OX 66 150 TRP overheating

[a1pescador]

I have a Yamaha 2001 OX 66 150 TRP that is beginning to overheat when I go over 4000 RPMs - under 4000 RPMs - no problem. I am probably not getting good water circulation through the motor although I have excellent water pressure and my water pump has been replaced recently. I have been told of two solutions - 1. run some type of cleaning/acid mixture through the motor to try and clean it out - or - 2. manually clean the water passages. Any opinions on which one is best? The manual cleaning is much more expensive @ 900.00.
Thanks,

[Sequoiha]

I would start with the thermostats and pressure control valve first, if the pressure control valve is stuck closed you can have a high speed over heat.

[scofflaw]

muriatic acid worked for me with a similar issue.

Lower unit off, stats out, pour the stuff in and stand back and watch the show. Best 4 bucks I ever spent

[99yam40]

I have flushed some motors by dropping the lower unit and hook up a hose directly to the water tube going up to power head, pull the stats , rig up a way to inject compressed air into the water that is going into the motor, turn on water fully letting it flow out the stats and exhaust, and hit the air from time to time.
It shakes up a lot of stuff that accumulates in the motor as long as it is not attached well to surfaces.

If the water pump housing was not replaced, you may want to inspect it for signs of melting.

If all else fails do a search for Ridlyme marine descaler,
I have read on forums it does a good job of cleaning mineral deposits

[TownsendsFJR1300]

Some links for the chemical treatment:

http://www.yamahaoutboardparts.com/f...g-th19434.html

http://www.yamahaoutboardparts.com/f...m-th23666.html

Has the engine been regularly flushed out with fresh water?

Used in salt water?


**We had to pull the heads on my neighbors 200HP, Yamaha 2 stroke, got over heat alarm and RPM slow down after about 4,000 RPM's.

We pulled the heads and the lower water passages, were easily 90% clogged. I don't know how the engine ran as good as it did. Manually scrapped out all the salt, ran great after that. Maybe $125 in parts. A fair amount on time (not hard, just time consuming)...