Please help! Overheat problem I can't solve.

Hi Guys. This is my first post. I have read every possible post about overheating yamahas. I have a 1998 90 hp. It runs strong, but when I bought it, I immediately noticed the previous owner had removed the tstat..which should of set me off. I replaced the tstat, thermo switch and new impeller kit. Also added a heat sensor to monitor heat. Motor heats up too much when idling and 'pee' is very weak during idle. When running, pee pressure increases up, but then motor quickly gets too hot and switch puts it into safe mode.
1) Am I correct in assuming I must have a blockage that is still allowing the 'pee stream' to get through? 2) How on earth do I find a blockage that is somewhere in the middle of the engine? I can't find any good diagrams. I have the manual but the one diagram is useless. 3) If I have been overheating this engine multiple times, what do I do in attempts to fix any damage i may have caused? Please help! I'm at my wits end with this.

[boats.net]

By removing cylinder head and exhaust plates you can get to water passages. Clean water passages in block and head and look for holes corroded in head and exhaust plates through into water jackets.

[Brisco58]

I would replace the PRV with the new mushroom style one before taking of the heads.

Thank you so much for the quick replies. I can not find a PRV anywhere on this engine. Do the 1998's 90hp engines have one?? If so, where is it?

I guess I'll be removing the head and exhaust plate.....wish me luck. It's a first for me. I'll report back.

[Hamfisted]

No PRV....

The V-4 and V-6 motors have a PRV, but not the smaller motors. Their waterpumps don't put out the water pressure that the bigger motors do, so relief is not a problem. Best bet is like mentioned already, pull the head off and inspect / clean the water jacket and passages as good as you can.



- Mike

Thanks, Mike. This forum is the greatest damn thing ever.