[Rhodes22-list] Yamaha (non) cooling system.

[Robert Fuller]

Rare post from dedicated reader :
I have little mechanical ability and paid a free-lance mechanic to  
change the impeller on my Yamaha 9.9 with a total of less than 75 salt  
water hours on it after 2 years. Rapid onset of problem. Impeller was  
fried.  Still didn't pee right and today we found the cooling tube  
running from the lower unit up thru the oil pan was more than 50%  
occluded by a lining of soft corrosion (also extending on up towards  
the motor head).  He says the basic problem is yamaha uses substandard  
aluminum  in the oil pan (and he has seen pans expand and burst  
through motor housings).
I flush the motor religiously for a timed 10 minutes after every short  
use.  Mechanic further claims the thermostat can cause flush water to  
remain in motor rather than drain and that this can be remedied by  
drilling a small vent thru thermostat.
I have never seen this problem reported in several years of reading  
posts.  Does it make sense to anybody?  Other thoughts?  Especially on  
preventing recurrence?
Lower unit and powerhead currently in his shop where he plans to check  
functionality of water pump and see if I blew head gasket. (back  
pressure then impede water flow).
Bob in Cortez, Fl.