over heating

[steges101]

Hello All heres my delima i have a 1986 150ETLJ one of my heads overheats and the other does not. i just replaced the water pump. i removed the head to check for a blockage and could not find any. any ideas?
Thanks John

[mitch]

thermostats been changed ?

[steges101]

yes and I ran the engine with out them and it still overheated on one side

[newatthis]

my overheat problem

I've been having overheat issues with my 1993 200 hp, at higher rpm's, about 4500 the alarm would go off and the temperature with an infrared thermo would be around 140 degrees, at the bottom cylinder at the top it would be around 120 which may mean the thermostat's were working. Yamaha Tech did this when the alarm went off on a test ride.

I changed the water pump first, still overheated, then thermostat's, still overheated, then poppet valve, still overheated,.

I'm now in the process of putting my water jackets back on, after having them bead blasted, not sure about any zinc coating at this point.

When you say you saw no blockage did you take apart the heads till where you could see around the cylinder's?

This was my problem, or at least I hope, I'll know when I put the parts back on.

Good luck!!

[steges101]

yes i did take the head off and i could not find any blockage I also checked the popit valve. I dont know what to check next.

[newatthis]

I've read where the thermal sensor could give a false readings. Do you have a infared thermo that you could point at the heads and see what the temperature actually is?

When you took oof the heads how hard was it to replace the gaskets. That's next for me.

[steges101]

Yes i have an infared thermo one side was 135 the other was 180 im thinking that the High Preasure Valve was stuck open. replacing the gaskets was easy just make sure you tighted the bolts to the proper #

[99yam40]

yes and I ran the engine with out them and it still overheated on one side

water cooled motors need the thermostats in place for a restriction to help push water through the motor properly. If you remove completly the water flow could a problem, it is the same on automotive motors also.
Thermostats are easy to check in a pot of water as you heat it up measure temp and see when it opens, how far it opens, and when it closes back.
Or just put new ones in.

PRV stuck open can cause a low RPM overheat problem but not high RPM problem, unless the water pump just is not pumping enough water.

[steges101]

Thanks everybody it was the prv valve