Hi all, I have a 2006 Yamaha 8hp 4-stroke with a difficult to pinpoint cooling issue. At mid-high RPM with the engine under load, flow disappears from the telltale. I can rev the motor to the limiter in neutral and water flow remains perfect, the issue only occurs in gear and only at higher revs. When I back off the throttle, flow returns and it feels hot.
Waterways appear clean and the impeller is new. I was thinking it could be the head gasket, but compression is an even 180psi, oil is clean, and the motor runs strong. It seems like exhaust pressure in the cooling system could be the cause. I’m hesitant to remove the head just to check the gasket.
Would it be possible that the head gasket is still bad with good compression readings? Or is there another part of the motor that could be causing exhaust leaks into cooling passages? Any other ideas?
Cheers
Waterways appear clean and the impeller is new. I was thinking it could be the head gasket, but compression is an even 180psi, oil is clean, and the motor runs strong. It seems like exhaust pressure in the cooling system could be the cause. I’m hesitant to remove the head just to check the gasket.
Would it be possible that the head gasket is still bad with good compression readings? Or is there another part of the motor that could be causing exhaust leaks into cooling passages? Any other ideas?
Cheers