2005 Yamaha F225 thermostat housing hole

[Tclaude]

Went to leave the dock and noticed water coming out of the front of the cowling (not a normal thing), pulled the cowling off and look what I found! water shooting up from a hole where the thermostat is installed. Upon removing the thermostat we found that the back side of it was caked with salt sludge which had bridged between the thermostat and the side of the case housing. That probably cause a dis-similar metal reaction and slowly ate the area away.

Pulled the other side and found a similar issue but not quite as advanced.

Bottom Line> running water through the system using just the garden house attachment will not properly flush out the block cooling passages. Once the cold water hits the thermostats they will close off not allowing enough time to flush out the block. (deposit build ups then occur behind the thermostat).

Page 52 on the Yamaha owners manual clearly states that to properly flush the engine you must use the flush attachment (muffs) and run then engine at a fast idle for several minutes. Then turn the engine off and hook the hose up to the garden hose attachment and run water through it for 15 minutes.

Needless to say I have not been doing step one since I got the boat, only step two. I am having the bad spot sleeved and hope I have not destroyed my engines by not properly flushing them out. Time will tell if I have to replace the block.

I see to many Yamaha owners like myself that only run the garden hose and don't flush with the muffs and the engine running. If you damage the block it can be 3-4K worth of repairs easily.

From now on it will be salt-away, muffs and garden hose for my engines...Hopefully I will not start bleading money over my mistake.

[pwrman34]

I too had a problem with one engine and had to replace the block, i am curious to see how the sleeve makes out for you. Yamaha stated replacing the block was the only way to repair as the existing hole would probably only continue to enlarge with other types of repairs.

[Tclaude]

Am putting the boat back in the water this weekend, I will leave an update on the sleeve repair..I have sure changed my flushing procedure after this scare...

[Tclaude]

just hoping to get maybe another 2 years out of the engines, that will make them 10 years old and they have lived there whole life in South Florida setting in a slip. 10 years for outboards is about all I expect down here....needless to say the cost of repairing these Yamaha 4 strokes will probably push me back into an inboard boat next time. You change out and throw away the risers every four years and you are set to go, unlike a slowly corroding out block on a outboard...I can get two fuel injected crusaders for the cost of one F225 outboard