I am going to put this out there for all our combustion engine Guru's. We put these I/O's and O/B's away with nothing internally i.e. antifreeze or water. So that means there is only air and some moisture (water) and or some antifreeze internally. Fe+O2+H2O= RUST. I can put my sportscar away without doing much because she is full of antifreeze. The snow machines are put away without doing much because the chance of freezing over the summer is nearly impossible. My wife's lawnmowers I do nothing to the engines. When I took a small engine repair course a few years ago the instructor had us dissect a very old 9.9. The thing had rust everywhere in it.
The million dollar question. Why won't rust form in an engine left free of any liquids for any period of time? I'm thinking if it has had all the plugs put back in where O2 can't get in the O2 that was trapped when the plugs were put in isn't enough for FeO to form or is it FeO2O3, it's been a while. What about air getting into the combustion chamber through a fuel system? Left long enough like the old 9.9 we took apart will rust eventually form? Sorry, perhaps I should have started a new thread Mods. I'm thinking the questions are directly related to the OP. Let me know and I will gladly move it. Please advise.
rust does form. heck rust will form on fresh metal within a few days from the humidity (unless your in Arizona). aluminum starts to oxide after a few hours
in a raw water cooled I/O, the first time its ever fired up in the water.... rust starts to form. rust forms more slowly with just fresh water, and about 10x as fast in salt water.
pulling the drains and allowing air in there, it does rust a bit faster than if water is simply running thru it.
however here is the rub..... Rust never sleeps. once the iron starts to rust, you cant stop it without mechanically removing it.
the only way to prevent rust is to start with a heat-exchanger on the motor from day 1. order the boat with fresh water cooling and change the coolant every few years as the coolant breaks down and becomes acidic promoting rust.
that being said, a fresh-water only motor will last about 40-50 years with proper maintenance prior to needing to deal with rust-thru. however the motor will most likely have been murdered long before that by lack of maintenance or lack of winterization or the boat will have been sold 3-4 times prior to that being the case.
a salt-water motor has the manifolds last about 7-10 years. heat accelerates the rusting process. the block and heads will last about 20-30 years prior to rust thru, however the intake manifold may not make it that long and may rust out sooner. the amount of corrosion that my result from the bit of air in there over the winter months really doesnt effect the system that much as the salt has already aggressively started attacking the iron from day one. this is why you cant add a heat exchanger to a salt-water motor after its been run in salt.
the only way to prevent rust is to start with a heat-exchanger on the motor from day 1. order the boat with fresh water cooling.
so the argument that anti-freeze to an I/O prevents corrosion is valid, however the amount of prevention is so slight that in the grand scheme of things, it doesn't matter. the motor is still rusting away.
regarding rust and the motor. if you want to prevent rust in the combustion chambers, fogging is required and that should be followed by pulling the valve covers, and loosen all the rockers as well. the oil film from fogging only lasts about 6-9 months when exposed to ambient air. closing the cylinders off extends the time the oil film is present. it also prevents critters from building nests in the cylinder bores as well as prevents valve springs from taking a set.
I would be more concerned with mice and insects making nests in the motor than I would be of rust.
