The cool­ing is a bit raw

Canal Boat - - Back Cabin: -

QMy BMC 1500 has a raw wa­ter cool­ing sys­tem. Wa­ter flows from a sea cock with leaf fil­ter, via a Jab­sco pump to the en­gine block, en­gine pump, ex­haust cooler to a pipe into the ex­haust.

There is no filler cap on the ex­haust cooler. There is a header tank, but again no filler. Why a header tank with­out a filler? Does it need bleed­ing? How does it deal with silt in the en­gine block wa­ter­ways? How do I win­terise it? The boat’s doc­u­men­ta­tion in­cludes an in­voice for an­tifreeze. Is there a way of do­ing this with­out killing the fish in the canal? FROM: PETERI, via the CB web­site

ATONY REPLIES... The raw wa­ter pump will fill the en­gine and the header tank, so you do not have to do any­thing about fill­ing it, and it should bleed it­self.

Some silt and limescale will set­tle in the bot­tom of the en­gine block but won’t cause prob­lems for sev­eral years. If you want to clear it out you will need to re­move one or more core plugs, hose the mud out, and fit a new plug.

To win­terise a con­ven­tional raw wa­ter-cooled en­gine you can take the ther­mostats out, turn off the sea­cock, hold a very large bucket un­der the ex­haust and run the en­gine on fast idle while you pour a 50% an­tifreeze mix­ture down the strainer un­til blue wa­ter comes out of the ex­haust. How­ever, on your sys­tem it may leave pock­ets of pure wa­ter be­hind. You will have to use drain plugs or taps on the en­gine block and man­i­fold. Poke some stiff wires through the drain holes to make sure they are not blocked by rust and mud. Turn the sea­cock off and re­move the Jab­sco impeller.

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