Volvo Penta MD 2020 1994

by Simon
(Brittany, France )

Drain tap removed from block, black sludge behind

When I tried to drain the fresh water coolant, nothing came out of the drain tap on the starboard side of the block. I unscrewed the tap to find that the passageway in the block is full of a soft black substance. The stuff smells a bit like soot but not strongly.

Fearing a major internal blockage I removed the fresh water pump and the heat exchanger. None of the passageways revealed have any signs of a blockage although the tubular brass insert from the heat exchanger was covered in a fine black substance. Both that and the little bit of black sludge I excavated from behind the drain tap are easily washed away with tap water.

The boat is new to us and the engine was run for several hours at the end of last season without any signs of overheating. The engine starts easily and there's no noticeable smoke in the exhaust.



Obviously I'd prefer to not have to dismantle the engine completely so I'm hoping someone can suggest a viable way to free the blockage. The boat lay unused for several years before we bought her so the engine probably hadn't been winterised for a while. We'll obviously carry out full winterisation from now on...