Understanding colling/exhaust

I have a bit of experience with other small engines, but am just learning about outboards. I have a yamaha 6HP 2-cycle. Could someone tell me if I am correctly understanding how the cooling and exhaust systems work?

1. Water is pulled in at the water intake below the antiventilation plate
2. Water is pulled up and runs through/around the engine block
3. A small part of the water is allowed to escape via the tell-tale
4. Most of the water is dumped into the inside of the midsection
5. The exhaust is also ported into the inside of the midsection
6. The pressure from the exhaust forces the water and exhaust out through vents in the center of the prop

Is all that correct?

Also, any book or online resource that does a good job of explaining all the essential basics like this (with diagrams)?

Re: Understanding colling/exhaust

cheers !

especially on the high tech 6hp yamaha 2 stroke keep it simple :

the impeller sucks he water below the cavitation plate , pulls it through the block and exhausts its via the exhaust. thats all

Re: Understanding colling/exhaust

Well you have it correct for what you described. On an inline motor, there is usually an exhaust port cover that is water cooled, as well as a head and cylinders that need cooling. So the water is pumped up into the block, cooling the cylinders, cylinder head and then it pours down the exhaust side of the motor, cooling the exhaust and the block. Most motors have a thermostat which allows the cooling water to recirculate until the motor reaches operating temp. Some of the water is then expelled to maintain that temp.

Re: Understanding colling/exhaust

OK. Great. Now....I'm getting ready to convert my Tohatsu 8hp 2-stroke into an electric saildrive. The powerhead is coming off and being replaced with a DC electric motor. I intend to permanently mount the drive leg through the hull low enough to service the lower unit from outside and allow clearance for a 12-14" folding saildrive prop and fiberglass it in solid (with vibration dampers of course). I also plan to trim off all the cavitation plates and fins, the skeg, and any other extraneous "bumps" on the drive leg to keep her as "clean" as possible. I no longer need (nor want) cooling or exhaust passages. The electric motor will cool itself (and obviously not emit any exhaust) so I'm considering filling the passages with closed cell foam and capping off with epoxy. My only concern is the water pump/impeller. The drive shaft runs through the pump and the impeller is on the shaft. Does anyone see any reason I can't just remove the impeller and pump liner and let the shaft spin inside the empty pump housing?

Re: Understanding colling/exhaust

bcbit01 said:

My only concern is the water pump/impeller. The drive shaft runs through the pump and the impeller is on the shaft. Does anyone see any reason I can't just remove the impeller and pump liner and let the shaft spin inside the empty pump housing?

Click to expand...

No reason not to remove the impeller and pump liner.

Re: Understanding colling/exhaust

Would stay with anticav plate and just remove impeller & key, will keep complete impeller housing inside leg and just seal the lower water pipe's grommet with silicone or plug. Just in case you would like to use it again or sell a complete original lower unit as spare in a future.

Happy Boating

Re: Understanding colling/exhaust

+1 - I whole heatedly agree - Doubt your expecting to resell unless with the boat.