Cooling Water Path through 2 Stroke Yamaha Outboard

[Jim Hawkins]

Trying to educate myself tonight to solve overheating issues on several motors.

I'm looking for the path cooling water takes through a Yamaha "2 Stroke" , such as -

Pickup - Water pump -Thermostat - Exhaust - Cylinders - Exhaust - Prop

Not sure if I have that in the right order. Also, as far as the tell tale I can figure that part out by following the hose.

Also, is the path the same for a 4HP? 6HP? 50HP? (All Yamaha)

 

[boscoe99]

There are as many different cooling water paths as there are Yamaha models. The paths are not the same.
Here is the path for a 30 HP two stroke.

 

[boscoe99]

V6 four stroke water flow.

 

[Jim Hawkins]

There are as many different cooling water paths as there are Yamaha models. The paths are not the same.
Here is the path for a 30 HP two stroke.

Thanks Bosco, that 2 stroke diagram looks just like my 50HP. In my case it sure looks like a very cruddy Thermostat making problems but I want to flush water back and forth through the passages while I have the lower unit and thermostat out and that diagram and flow chart is just what I needed.

 

[Jim Hawkins]

Also, before I do any damage,

I want to flush water through the motor to check for obstruction. Starting at the T-stat opening (with the lower unit off) I want to shoot water and/or air in both sides. Then backwards through the exhaust where the tell tale exits and up through the water tube above the water pump. Just basically clearing out water passages back and forth from whatever access points I can get to.

Is this safe to do?

 

[99yam40]

just for the heck of it, i will tell you how I flushed a bunch of stuff out of my brothers C60.
with lower unit off and the stat removed (cover still left off),
I hooked up a water hose to the pipe heading to power head,
I also rigged up an air hose to that water hose.
turned on the water and then shot blasts of compressed air into the water hose where it hooked to the pipe.
this caused a bunch of agitation up inside the cooling passages and forced a lot of sand/shell pieces up and out of the stat opening and out of the prop hub exit.
maybe that was a bunch of scale or corrosion flakes also

 

[Jim Hawkins]

That's along the lines of what I want to do, only I want to go back and forth both ways maybe even getting a shop-vac in on the action. Afterwards, I thought I'd put the lower unit back on and run the motor in a tub of vinegar and detergent for a while before repeating the process.

I just want to make sure I don't lodge something where it shouldn't go and make problems.

 

[QBhoy]

Often it’s just the tell tale that’s blocked with salty crud deposits. Worst case, yeah the whole lot could be blocked. Is it not pumping water out the lower unit ?

 

[Jim Hawkins]

Often it’s just the tell tale that’s blocked with salty crud deposits. Worst case, yeah the whole lot could be blocked. Is it not pumping water out the lower unit ?

I didn't think to see how much water was coming out of the lower unit before I started this repair. Knowing what I know now, I see your point. What I had was a strong flow out the tell tail that turned to boiling hot water. That made me look to the T-stat which, upon inspection, could in no way be mistaken for a working one. I decided then my best course would be a thorough flush with the lower unit off but short of pulling the head and exhaust cover. Once water was flowing to my satisfaction I would replace the thermostat, water pump and replace the lower unit.

My question about the flow of water was so I could evaluate what the water did as I pumped it back and forth through the various orifices.