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Dry Doc, you are right!! To tell someone not to flush their engine(s) borders on being un-American. However, my 2 150 Yami ox66's have never seen fresh water in their cooling systems. They are 3 years old with just over 700 hours on them.
I recently replaced the original thermostats with 4 new ones (preventitive maintenance) and had a great opportunity to observe any corrosion build-up in the water passages. There was nada, nil, zilch corrosion. The coating that Yamaha uses on the channels looked brand new. Even the thermostats themselves were clean; and although the brass, copper and bi-metal-coil were discolored, there was no corrosion. The rubber thermostat seat was flaky, but after 3 years, that is expected.
I frankly believe that if you run the engines at least once per month, flushing is totally unnecessary and an enormous waste of time. My boat is in the water 24/7 and I usually use it weekends only.
I am curious about the two opinions (gaefranz and and OutOfTheLoop) regarding not flushing in the tilted position. They are different, so does that mean people think there are 2 potential problems with tilted flushing? It is hard to imagine that engines would suffer either of the problems mentioned from running in a tilted position. Is there any proof to back up these comments?
I have always flushed with the engine tilted up (running and not, depending on whether I am using the top flush port of the muffs). My mechanic said there are no problems with doing so.
I suspect the great majority of people do it that way (particularly on trailered boats) and if it was a problem I think there would be a lot of outcry and the engine manufacturers would put warnings in their brochures and on their web sites. I don't recall ever having seen either.
So is there some evidenceto support these assertions?
Frank007 - I would think that the preference would be to flush with the engine down since that is the natural position the engine should be in when running. Second, by keeping the engine down, the water won't pool in the powerhead.
I can't remember if I read it in my manual, or was told to by dealer. But my 200 Yam was to be flushed with the motor down and not to use muffs unless they supplied water to each side.
I flush on occasion my 2000 Yamaha 115. Now that said my 1973 Evinrude 6hp has never been fushed stays on the boat year round, in salt water, and runs like a top. I will admit with the last waterpump change (couple of months ago, second since new) there was a bit of corrosion.
I had the same questions regarding flushing and the head mechanic at my dealer said it was not necessary but do so if it made me feel better. I called merc (twin 225 optimax) and was informed that it is perfectly acceptable to flush with engines tilted otherwise how could it be done in saltwater stored boats? This was in response to my question concerning potential damage if flushed in the tilted position. I now flush the engines around 3 out of 4 trips depending on how much time I have.
quote:Originally posted by TickleStik:
Frank007 - I would think that the preference would be to flush with the engine down since that is the natural position the engine should be in when running. Second, by keeping the engine down, the water won't pool in the powerhead.
I agree that down is the natural position of the engine, but why should that have any effect on whether the water flows through all the places it should get to? The water is pressurized by the water pump.
Absent some identifiable reason, this sounds like folklore that takes on unjustified credence by being repeated.
water cant get into the head from flushing, otherwise you'd be running with salt water in the head and we'd all be at the shop. Re: warping the heads, if I'm running in the Ocean, and cooling with water which is 60deg. or so, then come home and tilt the engines and flush with fresh water which is 60 deg or so how would that effect the heads?
Flushing Outboards 
