Rust flakes

[Lubak572]

I noticed my boat has rust flakes in manifold drains, and also when changing thermostat there was some in intake. This is my 2nd year on my boat, and I wasn't sure about maintenance done on it, so i am doing a lot of preventive maintenance on it. I have done plugs, caps, rotors, wires, fluids, greased steering ram, cleaned engine grounds, impellors, generator anode, cleaned flame arrestors, thermostats. Boat has 300 hours and ran well- no issues overheating or anything really. I winterized it using the 5 gal RV antifreeze jug on each motor. I did not drain it. No issue there, except when changing starboard T-stat- I was suprised at the rust flakes. So then I removed all 4 manifold drains and found rust flakes. Boat has the factory engine flush outs, and no visable rust issues on outside of manifolds. Boat did spend a season or 2 in salt in florida back in 2001 then on to Utah and Colorado where I bought it. I hauled it to Michigan. Should I be concerned? I plan to use a rod to get that crap out along with a long magnet. Would like to get another season out of them. No idea if they have been changed -I would think so. Will freshwater use here in MI cause this rust or is this a saltwater only thing?

 

[alldodge]

Even in fresh there will some rust, just the water on iron thing, it happens. If your manifolds are in good shape they should last a long time in fresh, even the life of the motor or more. Have a set I took off my 1995 during repower and they still look good sitting on a shelf.

Yours being in slat water, just have a real good look at them and you should be able to determine if they are getting thin.

 

[Scott Danforth]

Wet iron exposed to air will rust. Not uncommon. Most RV antifreeze does not have corrosion inhibitors

 

[QBhoy]

Keep it filled with antifreeze during storage in winter. Will stop the corrosion by a long way.
My 2003 has had AF in it every year....not a sign of any rust or flakes anywhere from drains. Speaks volumes.

 

[Lou C]

I've been filling my '88 up with marine antifreeze that has corrosion inhibitors in it every year and I do think it helps, when I took it apart the intake looked pretty good, the block cooling passages were not eroded at all, but the ones in the heads were, so I would up replacing them. I also never had a leak from the old style OMC batwings over the years I used them, with flushing them once at the end of the season and then filling up with AF when winterizing.

BTW, to the original poster, if you are winterizing a raw water cooled engine with the suck up AF via the muffs, DON'T! Because if you don't drain it first or remove the thermostat, that can result in a cracked block. Reason why, is the engine running on the water hose on a cool fall day, may not get warm enough to fully open the thermostat. And that is how the raw water would exit the block, the stat must open. What can happen is that all the AF will go out the exhaust, and the manifolds will be filled with AF but the block and heads may still have raw water in them. Always drain every drain, poke all holes, and disconnect the hoses needed to get all the water out FIRST. THEN, back fill with AF.

PS you're getting rust flakes, because the truth according to me, is that any cast iron marine inboard SHOULD be closed cooled, that is how they were designed to be when in an auto application. Raw water cooling is just a cheap inferior way, to cool a cast iron GM marine engine. Yes even in fresh water. Cheapness on the part of engine marinizers, is why.

 

[QBhoy]

Above is spot on !

 

[Lubak572]

Thanks will be draining them then refilling them with a good marine antifreeze with corrision inhibitors from now on