My Mechanic is at at a dead end. I have a 99 Vmax that overheats when idling. He replaced the waterpump twice, but still does it. It seams as the pee stream is steady, but not really strong. Running is fine. Just when idling like waiting for the trailer. Cant find anything wrong with it though. Anyone have any ideas?

Sounds similar to a problem my friend was having. He had a 225 vmax that had poppet valves that had become obstructed with debris and was starving the motor from cooling water. I believe that motor also has a thermostat that allows the motor to 'warm up' before admitting cooling water through the water jackets. The thermostat would be something that could cause these symtoms. Good luck.

Sounds like a plugged poppit valve, they have changed since your motor first came out, you can change to the new style one, check out the bass boat central's yamaha board, there is instructions how to go about cleaning and or replacing the poppit valve, it's stickied on the forum.

I had a similar issue, I checked my thermostats too, but didn't have any issue with them.

Check the poppet valve. Just a few grains of sand can stick this valve and cause water pressure issues and possible overheat. These Vmax like there water pressure. I have had mechanics tell me that they even have them overheat in the shop on the hose.....but if are ususally very good when in the water.
The poppet valve cleaning is not a difficult thing to do by your self. Just note how things came apart, and you MAY? need a new gasket if yours sticks and rips. Clean out the housing as well, and I bet it will fix the problem. ps. if your mechanic is at a dead end with this problem, and he hasn't thought of or cleaned the poppet, he may have taken you for a new uneeded waterpump, or he is not that good of mechanic. He should have known to look at the idle overheat as a poppet cleaning first and then move to other cooling issues.
Ryno.


My Mechanic is at at a dead end. I have a 99 Vmax that overheats when idling. He replaced the waterpump twice, but still does it. It seams as the pee stream is steady, but not really strong. Running is fine. Just when idling like waiting for the trailer. Cant find anything wrong with it though. Anyone have any ideas?