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Winterisation of any engine, but especially inboards, is probably the singular most important operation to be carried out annually to ensure the long life of your engine.
Here at Watercraft Services, we sell replacement parts for inboards and spend the majority of the week discussing engine and component failures with folks, which as a rule have been caused by bad maintenance and lack of winterisation over the years.
Most of these problems are caused by corrosion of some sort or another and many could have been avoided.

First of all lets have a look at some of the most common problems that manifest themselves after a long lay-up

  • Starter Motor Failure
  • Engine 'Tight' to turn over or seized
  • Alternator and Power steering belts screeching or shredding on first run out
  • Sterndrive Failure
  • Emulsified / Creamy engine oil
  • Creamy deposits in the Rocker cover
  • Alternator failure
  • Misfire
  • Erratic running and 'Spitting' during first runs out
  • Noisy Gimbal bearing (Fitted in transom Assy)

Lets examine some of the reasons these problems occur.
Firstly starter motor failure, this can be caused by corroded terminals or water ingress due to rain water in the bilges, or due to the fact that the boat has had salty water slopping around the bilges during the previous summer and the damp atmosphere down in there has caused the motor or terminals to corrode and cause failure, (we sell lots of starters in the spring)

Alternator failure, Usually similar to Starter failure above caused by corroded terminals and windings also siezed bearings internally, caused by spending the winter in a damp environment

'Engine tight to turn over' although this is a problem in its own right it can also cause starter failure as above especially with the later permanent magnet starters fitted to many engines. The engine 'tightness' can be caused by a number of problems some of which are,- Partial or total siezure due to rust on the cylinder bores, or Valves not sliding correctly due to corrosion on stems, or it could also be caused by a fault in the drive train especially with sterndrive engines, for instance, siezed gimbal bearing or bearings in the sterndrive siezed (both due to corrosion of the bearings) all could cause the engine to feel tight

Belts screeching or shredding during the first runs of the season, this is a classic in the spring, over the winter corrosion has taken place on the crankshaft pulley due to damp bilges etc, this in turn acts like an abrasive on the vee belts and wears them on the sides, thus causing them to start slipping and ultimately to shred through, this usually starts as the Alternator kicks in or the power steering is used. Quite often this can lead to a major engine overheat and the subsequent problems.

Sterndrive failure, this is usually caused by salt water ingress into the drive during the previous season, and as the water separates out from the oil during the winter, the salt water sits on the bearings and siezes them up, it also sits on the gear teeth and causes pitting, all of these things contribute to premature drive failure early in the season.

Emulsified or creamy oil and Deposits in the rocker cover, these are usually caused by water ingress into the engine itself, usually caused by either a cracked block or head, corroded cylinder block or head or corroded exhaust manifold(s) and very occasionally corroded inlet manifold. these deposits are usually accompanied by rough running and occasionally complete 'Hydraulic lock' where there is so much water in the cylinder that the piston cannot travel upwards at all, (this is usually accompanied by starter motor failure)

This image shows the inside of an average exhaust manifold, the arrow points to a hole.

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Misfire,'spitting' and erratic running, these could all be associated with corrosion problems as above, ie rust on the valves causing them to 'stick' or cooling water finding its way into the engine.These problems can also be caused by water in the fuel caused by condensation in the tank, gummy deposits in the carburettor / injection system, or damp in the ignition system

Noise from Gimbal Bearing or transom area, This is a complaint specific to engines with sterndrive legs and is the bearing which supports the drive shaft as it passes through the back of the boat between the sterntdrive leg and the inboard engine, this is usually caused by water entering into the protective drive bellows either from them being perished or from corrosion of the transom shield (gimble housing) casting.

To help prevent these and other Springtime nightmares follow our winterisation checklist as follows

This Assumes that the boat is out of the water and a hosepipe is available.

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  • Put a fuel stabilisation and water absorbtion treatment in the fuel tank (Diesels should also use an anti-bacterial additive)
  • Remove the fuel filter and replace (put a little fuel treatment in the new filter)
  • Fill the Fuel tank right up to prevent condensation
  • Check the level and condition of the oil in the sterndrive (if fitted) and drain and replace if contamination is evident, (alternatively remove the drive for further investigation)
  • Remove the Propeller to prevent seizure on the shaft (this can be left off during the winter),regrease in spring
  • Connect the water inlet to a hosepipe or fresh water supply (use flush muffs if sterndrive or outboard)
  • Turn on the water and run the engine up to temperature (10-15 mins) to flush out all the salt water in the system and warm up the oil.
  • Switch off the engine and water, change the oil and filter at this point (if needed) whilst warm, (Oil changes should always be done at the end of the season to prevent harmful contaminents sitting in the engine all winter)
  • Connect a short length (approx 4 ft) of hose to the flush muffs or water inlet and insert a funnel in the open end.
  • Re-start the engine and pour 50-50 water and antifreeze into the funnel and keep pouring until it comes out of the exhaust outlet then keep pouring until you have used about a houshould bucket full, then switch off the engine
  • Remove the Air cleaner or flame arrestor and restart the engine, set the revs at around 1500 RPM and spray fogging solution down the carburettor or air intake until the engine stumbles, slow the engine to tickover and continue to spray the solution until the engine stops or for about 5 seconds, then shut down the engine. THIS WHOLE PROCEDURE SHOULD NOT TAKE MORE THAN 15 -20 SECONDS, AS IMPELLER DAMAGE COULD RESULT. Replace the air cleaner / flame arrestor
  • Disconnect the battery and grease the terminals (Unless you need the auto bilge pump to keep working during the winter) the battery should be charged and discharged regularly over the winter
  • Remove the belts and either spray or paint grease on the pulleys to protect them from the damp air, (this can be washed off with a de-greaser in the spring
  • grease all the available grease points on the engine and drive and lubricate all the linkages and gear/throttle slides.
  • Grease all electrical connectors
  • Remove Impeller (where possible),rinse any antifreeze off and examine, then store until spring
  • Make sure the bilges are dry and no water can enter over the winter period
  • If possible put a tubular Greenhouse heater in the engine compartment to help keep things dry


Many Marine engineering companies make a policy of removing the sterndrive during the winterisation process, this is prudent in some ways as the condition of the universal joints and drive bellows can be ascertained, however, for the average person laying up a sterndrive boat this is not always necessary, as long as you are happy that the bellows are in good condition and have not been leaking.

The wisdom around the world regarding winterising varies, as some people like to drain down the system rather than pumping antifreeze through, however in our experience, these cast iron components, ie Block, head, manifolds,thermostat housing etc, remain serviceable for longer when left in a water filled condition than if air is allowed to come in contact with them.
An old Manifold or head which has been left open to air for any length of time will 'grow' and crack apart as they are full of corrosion within the actual material, whereas if left damp they do not, and let us not forget that these engines are usually marinised automotive engines (even from the larger manufacturers) and so are happy to be left full of water and antifreeze. (NOTE, In some instances antifreeze can soften the rubber impellers if left immersed for long periods) but in our experience this does not cause a new impeller to fail after one or even two winterisations, however Impellers should be changed every one or two seasons.

If the boat has to be left on a freshwater mooring, there is no option but to drain down the block, and manifolds, and if possible leave a heater in the engine bay.

Some owners like to remove the air cleaner and tape over the air intake, this is also a matter of preference, It certainly cannot do any harm.

Oil changes should be done as often as possible, but if the engine has only done low hours since the last change as long as the oil is still clean it is not necessary to change it every time.



For more information or to purchase winterisation products call us NOW on 01872 863777