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De-scaling OX66 200

Old 04-27-2020, 12:19 PM
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Default De-scaling OX66 200

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?
Old 04-27-2020, 01:34 PM
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Originally Posted by Lifeislarge View Post
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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Old 04-27-2020, 02:14 PM
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^^^^^^^^^^^^^^ that
Old 04-27-2020, 03:07 PM
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I'm saying nothing.....hang on, I just did!
Old 04-27-2020, 04:50 PM
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I think I'm going to just go ahead and pull it apart and clean it properly. What's the worst that can happen
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Old 04-27-2020, 04:58 PM
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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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Old 04-27-2020, 05:10 PM
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How strong is the pee, ?
Old 04-27-2020, 05:17 PM
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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.
Old 04-27-2020, 05:57 PM
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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.

Old 04-27-2020, 06:06 PM
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Originally Posted by biggesttuna View Post
How strong is the pee, ?
Pee is strong. I can cruise all day at 3500-4000 RPM but within a couple minutes of going over 4K the alarm goes off.
Old 04-27-2020, 06:12 PM
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Pee stream has nothing to do with it, do it properly and do it once.
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Old 04-27-2020, 06:55 PM
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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.

Old 04-28-2020, 06:26 AM
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Originally Posted by SweetD View Post
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.
I'm going to replace the head gaskets, thermostats, water pump and poppet valve. This engine is new to me and while I know it was well cared for, it's not much more work to start with a clean slate.
Old 04-28-2020, 07:39 AM
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You will know alot more when you pull the thermostats and poppet. If things look pretty clean you probably just need fresh thermostats and water pump.
Old 04-28-2020, 09:20 AM
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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.



Old 04-28-2020, 09:37 AM
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Woah! Good call to pull them and VERY good no broken bolts!

Definitely post up some post-cleaning pics.

Old 04-28-2020, 09:57 AM
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Originally Posted by SweetD View Post
Woah! Good call to pull them and VERY good no broken bolts!

Definitely post up some post-cleaning pics.
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.
Old 04-28-2020, 10:28 AM
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I'd buy them locally. To me it would be worth it.
Old 04-28-2020, 11:37 AM
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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.


Old 04-28-2020, 01:18 PM
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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?

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