OX66 225 low speed overheat

[kingfish]

Am back home from the trip up into Canada where the 225 resides; no resolution to the problem yet. If there is a blown head gasket, wouldn't there be some kind of loss of performance and/or visible water leakage around heads?

Yamaha Canada is telling the Marina that the next step is to remove the whole power head to see about bad gaskets, grommets, or whatever. Can't believe with the kind and amount of usage this motor gets and all in fresh water that this problem could boil down to something like this. I am at a loss and so is the Marina.

Isn't there some kind of schematic available somewhere that illustrates the cooling system so I could see where potential leaks could occur?

[Tiger51]

I have a 2001 OX66 225 hp. Can anyone explain the difference between the two thermo switches and the single temp switch. Will the horn sound if any one of these switches close.

[boats.net]

Thermosensors provide engine temp data to ECU, thermo switch activates the overheat warning.

[jrc]

same overheating at idle issue

Kingfish, I'm very interested in your story. I've got a 2002 150 TXRA, and have replaced the waterpump, thermostats, and pressure control valve (new style) and grommet -- and am still having the issue.

Not sure where else to go from here. As with yours, my engine seems to run fine throughout the full throttle range, and only exhibits the overheating at idle. Its frustrating though, because it's getting to be time to start *****ing for stripers here in the chesapeake!

Please update us as you get news!

[Tucker]

Gents, what has develped with these overheating problems. Courious minds need to know!

[jrc]

no news

Sorry Tucker, haven't been out to try mine lately. It's overheating after several minutes on the hose here at the house, but I'm hoping the next time I actually get in the water the problem disappears...not betting on it, but hoping...

[kingfish]

OK gents; here is what the apparent definitive answer to our problem was (just received an email with the explanation and photos from the marina in Canada.)

THERE WAS/IS A SPLIT IN THE WATER TUBE IN THE EXHAUST MANIFOLD!!

I currently don't know how it happened, how it *could* happen, why *no one* INCLUDING YAMAHA could diagnose it even after everything else was eliminated, how long the split has been there (initial low-speed overheat problems first appeared 4 years ago, were at least temporarily fixed with new PCV and became critical this spring), why there isn't a cooling system flow diagram that illustrates the entire system with all its various parts, how much this is going to cost, and however much that might be, whether Yamaha will be stepping up with any help. Not holding my breath on the last one.

The Marina finally found it by dis-assembling the motor. They (and I) concluded there was some kind of leak (NOT a blockage) in the water supply system ahead of the PCV; and there sure was.

I am relieved that the problem has apparently finally been found, but I am also extraordinarily frustrated with the steps, time and cost it took to track it down.

[99yam40]

Good to hear your problem has been found finally.
Could you post some pictures that they sent you?
I take it the tube is not the one heading out of the water pump, but a different one.

[kingfish]

I'm still working on getting a firm grip on just what this tube is, where it is, and how it is ordinarily accessed. It would appear from the service manual (which is not as clear in many areas as I would prefer), that the tube is in the upper housing and comes out of the top of the exhaust manifold. I pulled the lower gear case off this motor and changed out the water pump a number of years ago, and from my dim memory and the dim service manual, I think the water tube that the water pump fits into is a cast integral part of the upper housing, and the supply tube in question fits into the top of that assembly, so the offending tube does NOT come directly in contact with the water pump. I don't think. Hopefully these things will clarify themselves for me in the near future.

I don't believe I can post pictures on this forum (someone please correct me if I'm wrong about that). If you or anyone else is interested in seeing the photos, I'd be glad to email the to you.

[jf123]

Kingfish, PM sent. There is a way to post pictures. Send them to my private email and I can put them up. Interested to see since I am fighting a water in cylinders issue that may be similar. Thanks

[jf123]

I attached the pictures kingfish sent. Anyone know if this part is available through Yamaha?

[kingfish]

Thanks for posting the photos jf123 - I will have to learn how to do that.

The water supply tube is part of the exhaust manifold assembly in the service manual, is available from Yamaha and has been ordered by my marina.

For what it's worth, here's what the Marina had to do to get at it: "...To get at it we had to remove power head , exhaust adaptor plate, muffler, and lower unit . All that was left was exhaust tube !..."

[99yam40]

Does anyone at the marina think this split was do to water being trapped in the tube and freezing, or just a defect in the tube itself?

To post pictures. you scroll down the page when posting, you will find attach files under Additional Options. Click on the Manage Attachments. This will allow you to down load files from your computer or from the web, but they have to be small enough to meet the guide lines for the site. You will have to reduce the size using different software, and play with it to make sure it will go,

[kingfish]

Thanks for the tutorial 99yam40 - that seems simple enough! I didn't see your pm until just now - sorry.

The marina has never seen this before, but they are contacting Yamaha to inquire about it.

I don't understand how water *could* be trapped in that tube so that it could freeze. Unless the boat were in the water and the lower unit in the down position when temperatures dropped down far enough to freeze? I guess it's possible that at least part of that tube would be below the water line in that scenario. I'm still bothered by that notion though, as my observations have been that when water in a tube freezes, it pushes one way or both ways in the tube as it expands, unless both ends are tightly mechanically sealed. Which would not be the case here.

It is interesting to contemplate Yamaha's position regarding compensation to me or the marina if it turns out there was a manufacturing flaw. My cynical self is not holding his breath on this one as it seems that would be hard to prove, and doubtful Yamaha would admit it. Which is not to say I wouldn't give it the old college try if things start to point that way.

[jf123]

Any idea what type of metal the tube is made from? I was thinking freezing but like you mentioned it doesn't seem possible to where it is located. I wouldn't expect anything from yamaha on a ten year old engine. If they set that precident everyone would be running to them with every issue. Keep us posted. If I ever figure out what is causing my issue I'll let you know.