Yamaha 40 betol -91 cooling problem

[Lasse Lehtonen]

I have a -91 yamaha 40 betol outboard and I have recognized that it is cooling poorly when warm.Ok the problem is this : When I start the engine cold the water is coming out of the pee hole normally, but when I have driven cruising speed for a while and then slow to idle speed the water stream coming out of the pee hole is wobly and there is not pressure at all.When I put a bit more throttle than idle it pisses just fine again.This is weird cause engine idle rpm is the same when cold (700rpm) and when warm but the pee-stream is much weaker when warm.The owerheat alarm have never sounded but Im stil a bit afraid.In cruising speeds the stream is allways normal and there is a lot of pressure. Thanks for answers.

 

[Triton II]

Re: Yamaha 40 betol -91 cooling problem

Eki, the pee hole symptoms you describe sound completely normal. I worried about my FT60B doing exactly what you described and my dealer tank tested the engine and declared everything to be A-OK. Someone on this forum may be able to tell you exactly why the water stream pressure varies but it may be the water impeller has to push the water all around the engine once the engine is warm and the thermostat is open so the pressure reduces when warm? This theory sounds plausible, but I am not overly familiar with your engine so I could be talking out of my a&s!

 

[Lasse Lehtonen]

Re: Yamaha 40 betol -91 cooling problem

Thank you for answer. I hope it is not something more serious.I checked sparkplugs and they were all normal coloured (black) so I think water ending into the cylinder is not causing this loss of pressure in cooling system.