Yamaha 200 Ox66 Operating Temperature

[R4]

I have a 1999, 200HP, OX66, that recently developed a problem. The motor will not reach the correct operating temperature, and the result is ,it idles too high. After searching this forum for suggestions, the following was done: changed themostats (old ones were OK), checked poppit valve OK, and replaced thermo sensor. The engine still runs too cold ,digital thermometer registers 87 deg F on the heads. The water pump is 2-years old and has normal pressure, so I think this is not the cause. Can there be something causing the cooling water to bypass the thermostats? I have applied heat to the thermosensor, and the engine settles down to a normal 700 rpms. Open to more suggestions.

 

[rodbolt]

Re: Yamaha 200 Ox66 Operating Temperature

either some cyliders are not fireing or water is bypassing the T stats.

 

[R4]

Re: Yamaha 200 Ox66 Operating Temperature

Thanks for the reply Rodbolt. I will check to see if all cylinders are firing, but it seems they are. What can cause a bypass of the thermostats? The part of the heads where they mount are clean, and the T-stats seat well. Thanks again.

 

[99yam40]

Re: Yamaha 200 Ox66 Operating Temperature

maybe weak spring in PRV or hole in passages from corrosion

 

[rodbolt]

Re: Yamaha 200 Ox66 Operating Temperature

bad pressure control would be an indicate of low speed overheat not over cooling.
double check the pocket areas around the t stat seat.
do both heads stay at 87 degrees?
did you check for code 33 with a diagnostic test lamp?

 

[R4]

Re: Yamaha 200 Ox66 Operating Temperature

Hi Rodbolt. I was with my Yamaha mechanic when the test lamp showed a series of 3 blinking lights. He told me that it indicated that the motor was in "warm-up" mode. He is stumped. And yes both heads read 87 deg. What is code 33? Thanks!

 

[99yam40]

Re: Yamaha 200 Ox66 Operating Temperature

bad pressure control would be an indicate of low speed overheat not over cooling.
double check the pocket areas around the t stat seat.
do both heads stay at 87 degrees?
did you check for code 33 with a diagnostic test lamp?

Yea, sorry I forgot the PRV just dumps the water instead of allowing it to circulate through motor. One too many cold ones may have killed that brain cell that held that info.

 

[rodbolt]

Re: Yamaha 200 Ox66 Operating Temperature

aint nothing like some cold 12oz brain bullets.

water circulation on the 2.6 is through the block,heads and out the t-stat then down the water cover and into the exhaust stream.
code 33 is engine warming up or a bad water temp sensor or wire.
code 1 will appear after the block has reached 113 degrees.
thats why I am thinking somehow the water is bypassing the t-stats somehow.