Cooling Flow Question

1974 70 horsepower Evinrude

Does cooling water exit the with the exhaust through the prop?

If it does, where does the water enter the exhaust system?

As far as I can tell, the water leaving the power head is directed to the outside of the exhaust tube and inside the midsection housing. It drains through the slots above the cavitation plate.

Yes most of the cooling water goes out the prop.----Enters exhaust below the powerhead.

Water cools the prop hub. Can't say I know exactly where it enters the exhaust

I agree that it come out of the prop as well. I can't see how though.
I could only find 2 water outlets from the powerhead. They come from the 2 outlets of the waterjacket.
They get redirected via the adapter and the plate such that one dumps into the midsection housing in front of the exhaust and the other dumps into the midsection behind the exhaust. See pictures.

The midsection fills up with water and some blows out with the exhaust relief holes. I figure there must be a common route in there somewhere. But I don't know where.

That explains allot. Thanks.

I took another super close look at the cooling and exhaust systems and noticed a hole in the exhaust tube.
It is about a 1/4" diameter and 1" below the plate.

This would definitely let water into the exhaust, but the midsection would need to be almost entirely filled.

Then I remembered those holes on the back of the midsection near the top. I have heard that they sometimes spit water and/or steam.

So I dug it out. It revealed that water should fill the midsection to about 3" from the top at which point it overflows into a large passage at the back of the midsection. This passage leads to the discharge slots above the cavitation plate. So that's how a set water level is achieved through the full operating range of the motor.
The 2 holes at the back of the midsection are passaged to a location much higher up the midsection. More like 5/8" from the top. So the water level should never reach the holes. Maybe some splashed water and steam would come out.

The 1/4" hole in the exhaust tube is at least an inch above the water level in the midsection. Water should not flow into this hole. Exhaust should come out. This would exit the midsection through the 2 holes mentioned above.

So, I still don't know how the discharge water gets into the exhaust stream to exit through the prop.
Any thoughts would be welcome.
Could it happen in the lower unit?
Does anyone know the pump output characteristics?

Those 2 holes in the middle picture spit out water at idle.-----If you were on water skis you would see water pouring out of those 2 holes.----Why all the fuss about this.------And no the water does not enter the exhaust in the lower unit itself.

While skiing behind my 73' 65HP, I could actually see when the thermostat opened and closed.
About every 10 seconds or so the exhaust relief water flow would turn on and off.

Jim

Thanks guys. The skiing observation is perfect!
So, when the thermostat opens, the increased waterflow completely fills the midsection, forcing water through the exhaust relief holes AND into the exhaust pipe.
This likely happens mostly at higher rpms as waterflow would also be higher.