Yanmar Paint problem

[SimonV]

I had a look at a 2001 Yanmar that was in a boat here Oz, what was unusual was the paint around the sump, lower block and the plate attached to the front of the engine was coming off in sheets. The exposed metal appeared to be aluminium and where the paint had been it was covered in a fine white powder. My first thought was that it was corrosion caused by electrolysis? Or that the motor had not been properly prepped before painting. Other than that the motor was extremely clean with no signs of oil leaks or rust. Could this paint problem have been caused by cleaning, degreasing with a cleaner such as chlorine.

[SJ34]

Maybe not degreased properly before painting? White residue maybe occured under void left by lifting paint? Just guessing.

What model Yanmar uses aluminum cases/block? My 3GM30 is iron.

[KeelHaulin]

Is it possible that the boat had taken on water previously? I'm thinking that the white powder is salt and corrosion of the aluminum which is underneath the paint and popping it away as it worked under the paint.

Are you thinking of re-powering Goodonya Simon?

[SimonV]

Hi Russ, Not for me. I just had a look at a C&C center cockpit for a friend the motor looks perfect except the paint problem. 50hp 2001 motor no rust on the block and the paint is stuck well except for the sump and and the plate that houses all the pullys at the front. I wish I had took photos. I have never seen anything like it before.

[KeelHaulin]

Could be due to either a mildly flooded boat (water filled to the highest point where paint is peeling) or the water pump was leaking water from the weep hole and dripping down onto the pulley and pan.

Otherwise; hard to say. It could be a galvanic reaction either due to inadequate zincs or possibly the aluminum is reacting with the metal in the paint; is the paint metallic? What year/size is the C&C is it 2001 or was that when it was re-powered? A Landfall 38 or ?