yamaha 200

my yamaha outboard 200hp 2 stroke mod.200AET over heats only at wide open throttle

 

When did you last change the water pump in the outboard's leg?
The impellers don't last forever.
After that check for obstructions and crud in the cooling passages.

 

As stated fit a new impeller every year if the motor gets a lot of use . Also check the water blow offf valve and the thermostats all at the same time . The blow off valve gets corroded and stays partly open so will bypass water instead of all going through the cooling system .
Its the importance of flushing you motor regularly

 

Ok, i have previously changed the impeller and removed ther thermostat and now i checked the the blow-off valve and all seems good, but the problem persists,syill over-heating at wide open trottle.What else should i try?

 

You removed the thermostat did you fit new thermostats ?? :?:

 

No, i did not. Can that create any problem ?

 

yes is a real problem ! specialy when motor is working hard and fast . The thermostat is there to slow the water flow down and redirect it to the right places within the block and heads . fit new or test the old and make sure they are working properly !!
Same thing happens with a car radiator !!

 

Just replaced the thermostat (new) ,went for a spin and the same thing is happening but only at full trottle.Dont know what else to try

 

how are you measuring that it is overheating?

 

Well the temp. gauge says so, the buzzer goes off ,i smell it and the block is estremely hot to the touch. There is even a reduction in the volume of water it pumps out.

 

Rovi ...go to www.iboats.com on the yamaha section of the forum...this is not a forum of engine fault finding adicts whilst iboats is .....
Can I suggest you could have an exhaust leak into the water cooling which is pushing back the water at WOT .
Tunnels concept of the thremostat is wrong ..usually just permits extra water to the cylinder head area once the engine is up to temperature ..in an outboard that is ..car different where it regulates the flow of water through the whole engine

 

Thanks pistnbroke