De-scaling OX66 200
#1
Admirals Club 

Thread Starter

I have a 2001 OX66 200 and the temperature alarm is going off anytime I cruise over 4000 RPM. Done a pretty thorough search and it appears the heads are probably caked with scale. Has anyone had any luck pulling the thermostats and filling the heads with de-scaler from the top or should I just bite the bullet and pull the heads? Just figured if I could somehow circulate a chemical with a pump and a basin going from the top it might work. If I do end up pulling the heads are there any tips and tricks that won't be in the manual?
#2
Senior Member

I have a 2001 OX66 200 and the temperature alarm is going off anytime I cruise over 4000 RPM. Done a pretty thorough search and it appears the heads are probably caked with scale. Has anyone had any luck pulling the thermostats and filling the heads with de-scaler from the top or should I just bite the bullet and pull the heads? Just figured if I could somehow circulate a chemical with a pump and a basin going from the top it might work. If I do end up pulling the heads are there any tips and tricks that won't be in the manual?
Some threads on here - just have to search - on using vinegar to flush.
Here you go....How to: Cleaning your cooling system with vinegar
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#3
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Join Date: Nov 2012
Location: Martin County Florida formerly Palm Beach County
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^^^^^^^^^^^^^^ that
#4
Senior Member

I'm saying nothing.....hang on, I just did!
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#6
Senior Member

Good idea, broken bolts will be your enemy, be careful removing bolts, use heat before if possible, if/when you break one, buy a good quality left hand drill bit.
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#8

Yep I did mine in a similar fashion to mr. Demeanor. I can’t say for certain what a difference it made but there was plenty of old nasty crud that got flushed out of the motor at the bottom of the pail when i was done.
#9
Senior Member

Just did mine via the removing the lower leg option and circulating Hammerhead descaler through the system with a pump. Really wasn't that tough - worst part is getting the lower leg back on but I had a helper. That thread posted above has tons of good advice and examples.
#10
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Thread Starter
#11
Senior Member

Pee stream has nothing to do with it, do it properly and do it once.
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#12
Senior Member

Could also be your water pump impeller. If it has not been serviced in awhile, the rubber impeller "arms" get deformed into a permanent shape that allows air to pass through with some water. This prevents enough water from getting up into the cooling passages, especially at higher RPMs.

See how curved the couple of arms are in the rear of this pic? Different from the rest. That's what I'm talking about. They allow air in with the cooling water.

See how curved the couple of arms are in the rear of this pic? Different from the rest. That's what I'm talking about. They allow air in with the cooling water.
#13
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Thread Starter

Could also be your water pump impeller. If it has not been serviced in awhile, the rubber impeller "arms" get deformed into a permanent shape that allows air to pass through with some water. This prevents enough water from getting up into the cooling passages, especially at higher RPMs.
See how curved the couple of arms are in the rear of this pic? Different from the rest. That's what I'm talking about. They allow air in with the cooling water.
See how curved the couple of arms are in the rear of this pic? Different from the rest. That's what I'm talking about. They allow air in with the cooling water.
#15
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Thread Starter

Heads are off. Pretty crudded up and given the fact that it's a single engine boat going offshore I feel better pulling them regardless. Literally took 30 minutes to pull them off (and NO BROKEN BOLTS!!!). T-stats look like new. Water pump next.


#17
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I took a ton of pics and will do a write up on the removal and replacement. Soaking in white vinegar now. The only challenge now is do I spend an extra $70 to get the parts in town today or wait for shipping from SIM Yamaha.
#19
Admirals Club 

Thread Starter

Aaaaand here we go. Poppet stuck solid. Probably could've gone here first and been okay for a while but I'm happy with doing the complete overhaul.



#20
Senior Member

Poppet won't cause high speed over heat, but, you have done the right thing, dig out all the crap you can from in the block as well, that looks pretty serious to me, I think your model allows access through the exhaust cover as well?