I'm in the middle of an engine swap in my boat. It has a Mercruiser I/O. The old engine (basically a GM 153) has been pushing out oil for years from blow-by, as well as spewing river water into the bilge from a crack in the block. (That's what bilge pumps are for, right?
) I've always kept ''bilge bags'' down there. (oil absorbing pillows) It would need a new bilge bag about twice a year, and they're good for 2 quarts of oil absorption.
So... now the new engine's in place and bolted down. The mechanic is rebuilding the out-drive now, and the only thing left on the engine is hooking up hoses etc. Hopefully, by the middle of this week, it'll be back in its marina slip. A few days ago, when the old engine was out, I took the boat to the car wash on its trailer.
I bought a can of Black Magic from my usual auto parts place. They had just received a shipment, and didn't even have it priced yet. Phil told me to try out out, (They had no idea how it worked, good or bad) and settle up later. (I did last Saturday, and it's only about $5 a can)
One word: WOW. When the spray hits the oil, it immediately starts to break up. We're talking about YEARS of build up, on parts of the Mercruiser shifter and trim unit where there's no getting to it otherwise with the engine crammed in there. Some of the dirt/grease was over 1/4'' thick. On the bilge floor, little brown islands started to form where the oil was breaking up.
I sprayed it all over everything, using about 1/2 the can. I drilled out a rusty drain plug in the transom while it soaked, then headed for the wash. (I have a new drain plug to install) At the car wash, the oil mess had turned into what looked like milk. By then, it had been working about a half hour or so. The ''milk'' just washed away and ran out the transom drain hole. There wasn't even really an oil sheen on the milky waste water in the car wash. That was fine with me, as there was a NO GREASE WASHING sign on the wall of the car wash.
The bilge area is squeaky clean now. A lot of stuff, like Gunk doesn't work that good, and always leaves a residue. Black Magic leaves surfaces like Dawn dish soap does a dish - there's nothing but a clean surface. I didn't bother carving off thick buildup with a screwdriver 1st, like you always have to with Gunk or other crap-cleaners.
I'm not sure about whether Black Magic contains oil eating enzymes or what, the website or can label doesn't really say, but it must have them the way it ''eats'' oil. If you have a greasy engine area(or whatever) to clean, don't waste your time with anything else.