ox66 Thermostat issues

[GradyGEO]

Hello All,

I have an issue that has puzzled everyone I have spoken with. This includes my mechanic, two local Grady White Dealers, the Yamaha customer service dept., as well as all of my buddies at the dock.

I have a pair of model year 2000 225 ox66 Yammies on my Sailfish, and have to change my thermostats at about 50hr intervals. I learned this the hard way after overheating on two separate occassions when I first purchased the boat. I flush each engine for 15min after each use, and have even tried altering the trim during the flush cycle between up and down as I saw some comments regarding this on the forum.

Everyone I have spoken to says I should be getting 200hrs on the thermostats, but I just replaced them again after 50 hrs and one was stuck open and the other three looked like crud.

I have about a 30 min. idle run to the inlet, and 50% of it is in water that is 4-6 ft. I'm so dar inland that the water at the marina is actually brackish, which I would think would help matters. Everyone I spoke with says that the depth of the water shouldn't be an issue. I'm lost on this one. Has anyone else had this problem?

Any and all comments would be much appreciated.

Thanks.

 

[seasick]

I replaced mine this year after at least three years of service and the old ones looked clean and still worked to spec. You should be getting a lot more life out of those thermos.
Are they oem units?
What does the crud look like? How did the chambers under the thermos look?
I don't think changing the till makes musch difference in flushing.
I assume you installed them in the proper direction

 

[GradyGEO]

Crud looks white and green...like they have been in for ever. They are Yamaha parts, purchased at the grady dealer, and my mechanic changed them the first two times, and I can honestly say that the guy I use is very competant. Said he never saw this before. I can't say for certain that I know what the inside of the chambers are supposed to look like, but they looked pretty clean to me, and the mechanic never saw anything alarming.

 

[Heavy Duty]

I had the same issue on my overnighter. Only had 25 hours on the motor and got a high temp alarm. One of the mechs at Norfolk Marine suggested flushing with Salt-Away before puting the boat back into the water and after changing the T-stat. He also stated to make sure and take a look at the pressure relief valve and make sure it is clean and that the spring is not in bad shape. So far it seems to be working.

HD

 

[seasick]

Crud looks white and green...like they have been in for ever. They are Yamaha parts, purchased at the grady dealer, and my mechanic changed them the first two times, and I can honestly say that the guy I use is very competant. Said he never saw this before. I can't say for certain that I know what the inside of the chambers are supposed to look like, but they looked pretty clean to me, and the mechanic never saw anything alarming.

Where does your flushing water come from?
At first I assumed the white stuff was salt buildup and the green was corrosion of the thermostatt but now I wonder if your flush water source is contaminated.

 

[no problem]

Since they are made of different metals, the green makes me think of corrosion. Maybe your boat has a stray current issue. I would check the condition of all the zinks and check for stray electricity. Just a hunch. good luck!

 

[GradyGEO]

The zincs all look good and I change those annually during routine service even though they probably don't need to be changed. The green definately does look like corrosion, and the white like salt. If I had the forethought of posting this I would have taken a picture before dumping them. Dumb on my part I guess.

I was figuring the salt build-up was causing the corrosion. What's the best way to check for stray current?

Another interesting thought however is the flush water source. It is from the fresh water at the dock that should be coming from the city water supply. Could there be something in the supply that would cause this? But then again I guess everyone else on the dock would be having the same issue.

This is good stuff guys...Thanks again for your tips.

 

[Tucker]

As for stray current, if you keep your engines in up/locked position and out of the water; stray currents are not a factor. I'm with Heavy Duty on Salt-Away. I've been reading about that stuff and plan to use in when I pull the boat this Fall. The prv poppet valve is also an item that needs to be change yearly. Don't think that's the problem, I just think you got a huge build up of salt inside the engines. This is a first, keep us posted with developments. The beauty of these forums is we all learn from each others misfortunes! We've all been down your road so don't feel bad! I'd also get on the Yamaha forum at boats.net. There are some real smart cookies on there all the time.

 

[DB]

You Change zincs annually...do you have money to burn?...they should last for years...how are your grounds? Are they all tight? Stray current could be killing thermostats...contact with water has nothing to do with stray current in your electrical system.

 

[seasick]

You Change zincs annually...do you have money to burn?...they should last for years...how are your grounds? Are they all tight? Stray current could be killing thermostats...contact with water has nothing to do with stray current in your electrical system.

Unless you are boating in your bathtub, I don't see zincs lasting many years. In my neck of the woods in salt water, one year, maybe two on trim tabs. For inboards, one year tops.

 

[GradyGEO]

Thank you guys...I bought the Salt Away on my way home last night and will be flushing away today and from here on out. I'm also going to check the wiring connections.