Overheating at idle

[ctrevis7]

I have a 2003 yamaha 150 2 stroke. It runs great at high speeds but overheats at idle. Could it be a thermostat if it only happens at idle? I thought it may be the poppet valve but not sure. It pees fine all the time and water pump was replaced this past summer! Ay help would be appreciated! Maybe an instructional video of how to replace these two things, as I do not have a manual!

Thanks

 

[99yam40]

Re: Overheating at idle

I would go for the PRV to see if it is sticking open.
Stats would cause it at all RPMs

 

[mygrady]

Re: Overheating at idle

Sounds like the poppet valve. I had one on my 225 that sounded an over heat alarm at idle or trolling speed. When I got up on plane it went away. You really need at least a basic manual. Your motor is not that old. We like to help but you need to help yourself a little bit.

 

[ctrevis7]

Re: Overheating at idle

Sounds like the poppet valve. I had one on my 225 that sounded an over heat alarm at idle or trolling speed. When I got up on plane it went away. You really need at least a basic manual. Your motor is not that old. We like to help but you need to help yourself a little bit.

I appreciate it guys! I figured it would be the poppet valve since it was only at low rpms. I will be picking up a manual as I just recently purchased this boat and previous owner didn't supply one! Thanks again guys

 

[Silvertip]

Re: Overheating at idle

The poppet valve opens at high rpm so if it was stuck shut the engine would overheat at WOT. The thermostat being stuck shut causes overheat at idle. When closed, it holds water in the engine to bring the engine to operating temp quickly. When it opens, water flow through it is sufficient for cooling at slow speeds. When at high speed, the open thermostat and the poppet valve come into play to allow more water flow.

 

[99yam40]

Re: Overheating at idle

If the PRV sticks open on that Yamaha it will dump too much water before it goes through the motor and will not let block fill up all the way at Idle, thus the top cylinders will over heat due to no cooling. At higher RPM the water pump pumps enough water to overcome this and will cool motor properly.
Normally PRV opens at high RPM due to the water pressure overcoming the spring tension keeping it closed, If it sticks closed it would cause exess pressure and more water flow through the motor, I do not see how that would cause and overheat at high RPM.

If stats do not open properly the heads will not get proper water flow and will overheat at all RPMs, high RPM causes even more heat and overheat even quicker than idle
This may be different on other brands of motors, but it is the way of Yamaha

 

[mrmamiller]

Re: Overheating at idle

I have a 2003 90HP Yami 2 stroke. It overheated at idle IN GEAR (600 RPM) in the water, but did NOT overheat at idle in neutral (800 RPM). In gear in water from 800 RPM up to 1200 RPM were fine also. Changed thermostat and poppet valve, no change. Pulled lower unit to look at impeller (was changed 3 months before I bought the rig). I found pieces of a previous impeller were left over in the passages. There is some question also concerning the gaskets that were used, not original Yami. After replacing gaskets and a good cleaning, all runs fine now. Not sure if your cooling system is the same, but that's what happened on my 90.