1999 200HP Yamaha???????????

[RABBITFISH]

When my 2001 Yamaha OX66 225 hp started to run hot while flushing, I learned many things............the thermostats were sticking slightly, and the PRV valve was a little dirty....I replaced the thermostats, cleaning the area as well as possible, removed and cleaned the PRV also......after doing these maintenence items..the water pressure guage showed 15 to 20 psi and no longer had a problem with overheating while flushing.....the telltale stream also improved. The water pump can send the water pressure up to the top of the motor only when the PRV is closed....... if it's open only slightly, it lowers the pressure and the water flow won't reach the top of the motor causing it to overheat at idle....When running at a higher rpm in the water, the PRV will open and release any overpressure........

[CaptJ]

Originally Posted by RABBITFISH

When my 2001 Yamaha OX66 225 hp started to run hot while flushing, I learned many things............the thermostats were sticking slightly, and the PRV valve was a little dirty....I replaced the thermostats, cleaning the area as well as possible, removed and cleaned the PRV also......after doing these maintenence items..the water pressure guage showed 15 to 20 psi and no longer had a problem with overheating while flushing.....the telltale stream also improved. The water pump can send the water pressure up to the top of the motor only when the PRV is closed....... if it's open only slightly, it lowers the pressure and the water flow won't reach the top of the motor causing it to overheat at idle....When running at a higher rpm in the water, the PRV will open and release any overpressure........

Guess changing tstats and prv will be the next step. But my main issue is that it has been doing this since day one NEW. Could be worse though, at least I am still on the water and motor runs great.

I appreciate all the input you guys are always willing to give. Just a puzzle I want to solve.

[spareparts]

I hate to ask the obvious, but does it over heat and act up when you put it in the water?

[CaptJ]

Originally Posted by spareparts

I hate to ask the obvious, but does it over heat and act up when you put it in the water?

Spare, in the water she runs awesome does not act up or overheat, knock on wood.

It is when she's out of the water that she won't piss a drop, with the ear muffs on.

As soon as I put the stern in the water I jump in the boat (still on the trailer) turn the key and she pisses water like a champ! No delay at all, motor does what it is suppose to do.

That's the part that has had me baffled. Again knock on wood, no problems in the water. I can run her for hours from idle and upto 5400 RPMs.

Maybe she just the salt water turns her on...

[RABBITFISH]

CaptJ.
Do you have a water pressure guage? My motor was doing the same thing until I began to worry about it and installed a guage....It reads from the top of the motor so I can tell if the water pressure is getting to the top. I had my neighbors motor next door running and his was spitting water like it was new but mine was so weak it looked like an old man, but it was ten years newer.......After discovering the PRV I took it out and gave it a thorough cleaning...re-installed........problem solved...It only had just a few grains of sand in it..evidently this was enough to allow the water flow to bypass the cooling system and dump out without reaching the reommended pressure.......It's a pain to reach, and it's a cheap part, but it plays a big part in the cooling system....

[CaptJ]

Thanks, I will try that, sounds like it makes sense.