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Yamaha 150 OX66 cooling diagram / clean out

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Yamaha 150 OX66 cooling diagram / clean out

Old 03-01-2021, 07:05 AM
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Default Yamaha 150 OX66 cooling diagram / clean out

Anyone have a diagram showing ALL of the cooling passages 1999 150 OX66? I will be cleaning them out and don't want to miss any!

I've had a bit of an overheating problem lately and have decided to physically clean out all of the passages (I've already tried flushing etc). Engine is used exclusively in salt water. I've owed it for the last 6 years or so and flush after every use, but no telling what the previous owner did or didn't do. Up until recently it has run flawlessly. Over the last year or so the overheat alarm has been going off at more frequent intervals - which indicates to me a build up in the cooling passages = less cooling. We shall see. I will remove the jacket covers and heads tonight and will report back with some pictures tomorrow.

Ryan
Old 03-01-2021, 08:14 AM
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What did you use to flush? I use the hammerhead Descaling fluid diluted to the directions, pulled the thermostats and ran it through the flushing attachment for three hours and was still getting calcium buildup flushed out of the engine. pulling the water jacket and head will allow you to physically scrape the junk out, but I've heard of horror tales with broken bolts. Good luck.
Old 03-01-2021, 09:32 AM
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start here: new Yam Water pump kit + wp housing and replace poppet valve with updated version (stretch the spring) --- replace thermostats too

I will not do a 100-hour service w/o replacing the inexpensive WP housing. They are plastic, they see a ton of heat and naturally warp.

Last edited by CTXOK; 03-01-2021 at 01:55 PM. Reason: bc
Old 03-01-2021, 01:46 PM
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Second the thermostats change. I had similar issue which went away as soon as I changed them out. Easy fix.
Old 03-01-2021, 02:36 PM
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Did you get the heads and head covers off? Just wondering how many broken bolts you encountered. But really that's the only way to get it internally clean. I've seen motors that were flushed religiously and had scale packing the cooling jackets. Also seen broken off anodes blocking water flow.
I've had the best luck using a small impact gun to shake and rattle the bolts out. Still had a few bolts break off though. Best of luck and post pics of the internals if you go that route. We're all curious!
Old 03-01-2021, 03:03 PM
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....

Last edited by CTXOK; 03-01-2021 at 03:42 PM.
Old 03-01-2021, 03:04 PM
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Same thoughts. T stats, pull head covers, replace water pump. Also shoot the heads with a infrared thermometer and see if they are in spec. The temperature sensors are in the heads. Maybe, just maybe....bad sensor. Probably not but ya never know.
Old 03-02-2021, 06:00 AM
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Originally Posted by m9000 View Post
What did you use to flush? I use the hammerhead Descaling fluid diluted to the directions, pulled the thermostats and ran it through the flushing attachment for three hours and was still getting calcium buildup flushed out of the engine. pulling the water jacket and head will allow you to physically scrape the junk out, but I've heard of horror tales with broken bolts. Good luck.
I flushed initially with Salt-x and then near straight vinegar. Flushed as you see in the pictures - engine running & thermostats removed. I monitored engine temp and shut off once at operating temp. I figure the heat would only help the flushing action. I did this for several cycles. This reduced the amount of crud in the engine by only a little IMO but it still did not solve the overheat. That's why I've decided to tear it down and clean it properly.






Old 03-02-2021, 06:10 AM
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Originally Posted by MakoDudes View Post
Did you get the heads and head covers off? Just wondering how many broken bolts you encountered. But really that's the only way to get it internally clean. I've seen motors that were flushed religiously and had scale packing the cooling jackets. Also seen broken off anodes blocking water flow.
I've had the best luck using a small impact gun to shake and rattle the bolts out. Still had a few bolts break off though. Best of luck and post pics of the internals if you go that route. We're all curious!

Not just yet. I only managed to get the t-stat covers off last night. I did however break loose one or two bolts on the jacket & head to gauge what I might be facing. The bolts on the jacket broke free very easily. The one I broke loose on the head I had to pull a bit harder than I would anticipate, but it broke free with a "KACK"! I plan to at least get the jackets off tonight. I'm thinking it maybe easier if i remove the lower cowl. How hard is that to do?



Before.

Before.

Right T-stat removed.

Left T-stat removed.
Old 03-02-2021, 06:45 AM
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We have twin 250's on our Intrepid. We occasionally overheat at low rpm after cruising. We need to flush....
Old 03-02-2021, 06:50 AM
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Another ping for a cooling diagram....or can someone verbally describe the route? I want to be sure I clear all passages.
Old 03-02-2021, 06:52 AM
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How to: Cleaning your cooling system with vinegar
Old 03-02-2021, 10:12 AM
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No need to take the pan off. A wobbly socket will get to those lower bolts.
As far as your water flow diagram: i have not seen a diagram that depicts the exact route but you will see when you get the heads off that the water flows around each cylinder and through the heads and head covers. Lots of small passages that will lead you to a lot of scraping.
Whatever you do, DO NOT remove the rectangular exhaust cover panel between the heads unless it is leaking. Guaranteed several broken bolts that are tiny. But do check your poppet valve that lives in that panel. It gets clogged a lot. Just a spring and a plastic mushroom looking piece.
Look for broken anodes hanging out in the water jackets. Also check your water inlet tube (in the midsection, have to remove lower) for cracks or damage. Got my ass kicked for weeks on an overheating OX66 and it turns out the water inlet tube had a long vertical crack.
Old 03-02-2021, 10:16 AM
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Just realized this is a 150. Sorry I was thinking 225/250 but parts may be similar.
Old 03-02-2021, 10:19 AM
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When was the last time you did a water pump/impeller change?

Reason I ask is I was getting overheat alarm and went through the whole flushing procedure with the Hammerhead product. It worked, but not nearly as much gunk came out as I assumed would.

On the other hand, I grabbed a water pump service kit and replaced the impeller, housing, etc. I think that was my problem as the impeller fins had hardened up and taken a "set". At higher rpms they let too much air by vs. cooling water. Hence the alarm at higher rpms.
Old 03-03-2021, 05:55 AM
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Last night I first removed the poppet valve. No issues there. Nothing was plugged or cocked. The spring and valve were changed out about 4 years ago.




Old 03-03-2021, 06:02 AM
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Next I removed the right side cylinder cover. I was pleased to find no passages were blocked off that i could see. In fact, most were pretty wide open. However, the internal surfaces are covered with what looks like some sort of rust colored layer that has been baked on. It is not super difficult to scrape off, but it has to be scraped off. Letting it soak in water over night did not soften it up at all.


Right cylinder head cover removed

Close up

Close up at top

Close up at bottom
Old 03-03-2021, 06:04 AM
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The cover was in about the same shape (still right side).


Cover

Close up top

Close up bottom
Old 03-03-2021, 06:09 AM
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Next, onto the left side. The left side looked a little worse overall than the right side, but still no passages blocked. Still the rust colored baked on stuff everywhere.




Left cylinder cover removed

Close up at top

Close up at bottom
Old 03-03-2021, 06:11 AM
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Here is the left cover.



Left cover

Close up

Another close up

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