The cooling is a bit raw
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.