An acquaintance has a 90's model Evinrude motor that is experiencing some overheating issues. It runs fine all day long at or below say 3500 rpm but if you run it past that it will set an overheat alarm. It has brand new water pump and t-stats professionally done. The mechanic thinks there is a build up of stuff in the water jackets/heads as it has been used in salt water a bit. The head bolts are corroded and he recommended pulling the head as a last resort. Is there anything you could flush the motor with to help get some more of the junk out of it if that is the problem?

I have heard of flushing the cooling system with vinegar or simple green or a couple other products but was wondering if anyone had experience with any of them.

When saltwater gets in a small space and dries up, the salt crystals "grow" and fill any gap available. It's almost impossible to "dissolve" it with heat or acids. (I've tried!) Plus, most anything you would use to attack the salt will attack aluminum, and probably kill your engine parts. I had a Yamaha 4-stroke that quit pumping water. I had to replace a copper tube that fed water to the powerhead, because it had clogged with dried salt. I suspect that you will have to disassemble the parts and mechanically dig out the salt. Not easy or fun. If you get it fixed, always flush with fresh water after use. Good luck. IslandJim

Been there, done that, never again, this is what I used.


http://www.rydlymemarine.com/

Amazon has a flushing kit that comes with everything. http://www.rydlymemarine.com/portable-flushing-kit/

My '89 Yamaha 150 ProV had same problem last fall - overheat alarm at high rpm even with new water pump impeller kit.

I looked into trying to flush the engine but didn't like what was offered - so decided to do it the right way.

I pulled the heads and cleaned the heads and water jacket passages with a solution of 40-50% warm water and white vinegar.
Let 'em soak overnight, rinsed with clean water, and then reinstalled heads wth new head, water jacket cover, and thermostat cover gaskets.

There was lots of crud built up in the water passages and some blockages just due to freshwater mineral build up over time. Engine never in saltwater.

Not a hard job & took my time - most exotic tool needed was a torque wrench to torque head bolts to correct value.

No more overheat alarm and water pressure is 20-25 psi when running now.

But - if the head bolts are corroded you might not be able to get them out without breaking one or more - that'd be a bummer.