89 200 h.p. overheat

[pine island fred]

Friend bought another boat and suprise, it has problems to. This just started. At a power setting above 3400 rpm, he gets an overheat. He has replaced the thermostats, ( no help) and today we replaced the water pump ( looked good). Found the woodruff key that goes between the shaft and impeller broken and corroded to the point of being non existant. I am hoping that the impeller was free wheeling on the shaft and not pumping enough at a higher rpm setting.
In the mean time I was considering a potential problem with the pressure relief valve mounted on the exhaust manifold cover. I know it is there but can anyone tell me just what this valve does? I must admit that I am spoiled by working 30 plus years, using manuals covering BOEING, P&W, GE, RR, ALLISON, they all have sections covering discription and operation of each and every part, what it does, why it is there. I dont expect YAMAHA to be so thorough but damn, tell me what the part does! Does anybody know? We did replace the valve today with a new modified part. If this does not work we will be pulling the head cooling covers. How many bolt head can I expect to snap off?
89 200hp 2 stroke. yamaha. Operated in salt water all its life. thanks FRED ( former pine island fred ) can sign in on old pass/uid.

 

[pine island fred]

Re: 89 200 h.p. overheat

Friend bought another boat and suprise, it has problems to. This just started. At a power setting above 3400 rpm, he gets an overheat. He has replaced the thermostats, ( no help) and today we replaced the water pump ( looked good). Found the woodruff key that goes between the shaft and impeller broken and corroded to the point of being non existant. I am hoping that the impeller was free wheeling on the shaft and not pumping enough at a higher rpm setting.
In the mean time I was considering a potential problem with the pressure relief valve mounted on the exhaust manifold cover. I know it is there but can anyone tell me just what this valve does? I must admit that I am spoiled by working 30 plus years, using manuals covering BOEING, P&W, GE, RR, ALLISON, they all have sections covering discription and operation of each and every part, what it does, why it is there. I dont expect YAMAHA to be so thorough but damn, tell me what the part does! Does anybody know? We did replace the valve today with a new modified part. If this does not work we will be pulling the head cooling covers. How many bolt head can I expect to snap off?
89 200hp 2 stroke. yamaha. Operated in salt water all its life. thanks FRED ( former pine island fred ) can sign in on old pass/uid.

 

[pine island fred]

Re: 89 200 h.p. overheat

Sorry, one finger typing and hunt/peck method I make mistakes. Should read I can not get in on my old pass word and uid . Does anyone else have this problem? fred

 

[Ray Neudecker]

Re: 89 200 h.p. overheat

Basically. the pressure relief valve is designed to keep the water pressure from getting too high and causing gasket leaks. Problems with it normally show up at idle or low RPM's.
I would get out the torch for heat to help get the head bolts out.