What is the best way to winterise the engine on a Hallberg-Rassy Monsun 31?
I own a 1978 Hallberg-Rassy Monsun 31, currently out of the water for the winter. It still has the original Volvo Penta MD11C engine. What is the correct procedure to winterise it properly so the block doesn't crack and it starts up reliably next spring?
Answer
To properly winterise the Volvo Penta MD11C on your Monsun 31, you must flush the raw water cooling system with fresh water and then fill it with a 50/50 propylene glycol antifreeze mix to prevent freezing and internal corrosion. You also need to change the engine oil and filter while the engine is warm to remove acidic combustion byproducts before they sit in the sump all winter.
Oil and Filter Changes
Run the engine up to operating temperature to warm the oil and suspend contaminants. If the boat is ashore, provide cooling water using a bucket and hose to the raw water intake. Extract the old oil using a vacuum pump down the dipstick tube. The MD11C sump holds 2.8 litres. Change the oil filter, usually a Volvo Penta 833636 or an equivalent aftermarket spin-on unit. Smear a little clean oil on the new rubber gasket. Tighten the filter by hand plus a quarter turn. Refill the engine with a quality mineral 15W-40 marine diesel oil. Never use synthetic oil in an old MD11C, as it causes the original seals to leak.
Fuel System Maintenance
Change the primary CAV Delphi 296 filter element in the water separator and the secondary spin-on filter on the engine block. Bleed the fuel system using the manual lever on the lift pump. Work your way up to the injector nuts until pure diesel streams out without bubbles. Wipe up spilled diesel immediately to prevent slip hazards in the bilge. Fill the diesel tank to the brim to stop condensation forming inside over the winter. Add a shock dose of a biocide treatment like Marine 16 or Grotamar to prevent diesel bug.
Flushing the Cooling System
The original MD11C is raw-water cooled. Seawater circulates directly through the cast-iron block and cylinder heads. Standing saltwater left over winter causes severe rust and scaling. Disconnect the raw water intake hose from the seacock and place it in a large bucket. Run a hose pipe into the bucket to keep it filled with fresh water. Start the engine and let it run for 15 minutes to flush out salt and silt.
The thermostat must be fully open for the antifreeze to circulate through the engine block rather than bypassing straight out the exhaust. An unloaded engine running ashore rarely gets hot enough to open the thermostat. Temporarily remove the thermostat housing and lift out the thermostat before adding antifreeze. Shut off the freshwater hose. Just as the bucket empties, pour in 5 to 10 litres of a 50/50 mix of propylene glycol antifreeze and water. Propylene glycol is non-toxic to the marine environment. When bright pink or blue antifreeze spits out of the wet exhaust at the transom, shut the engine down immediately. Never let the raw water pump run dry. It destroys the rubber impeller in seconds.