Engine Checks

What do you mean by engine checks?


Engine Checks
Most yachts have an auxiliary diesel engine to enable them to motor into and out of harbours, rivers and moorings and indeed to assist in passage making when there is insufficient wind or it is blowing from the wrong direction. It is also useful for charging both the engine start battery and the domestic batteries. See Boat batteries tips for more information.


Before we look at the engine checks it is good to understand a little of how things work and the diesel engine is simple. All it needs is a good supply of air, clean fuel and a clear exhaust. This all put together enables the engine to suck in clean air, compress this air with the clean fuel to create a squeeze and a bang which pushes the piston back and thereby turning or rotating the crank shaft to enable the cycle to be repeated in another cylinder the used piston on its way up the cylinder exhausts the spent fuel and air through the exhaust system.


Engine checks


The first thing on opening up the engine bay is to have a good look and using your senses sight and smell observe everything that is presented.


You are looking for anything obvious, liquid in the bilge, mechanical things not in the right place bolts, screws or washers in bilge, odd smells.


        Liquid in the bilge, identify what it is usually by its colour,

        Black is generally oil therefore you are looking for an oil leak.

        Blue or green is engine coolant was it over filled and this is the excess.

        Rainbow colour is associated with fuel.

        Clear is water which could be either salt or fresh.


It is a good idea to always leave the engine bilge clean and dry so that you may identify the early stages of a problem. It is illegal to pump out into the sea the contents of your engine bilge.


The Fan belt is driven by the crankshaft pulley and drives the water pump pulley enabling engine coolant to be circulated round the engine it also drives the alternator pulley which generates AC power to top up the batteries.


The visual inspection is does it look in good order, is it clean without any frayed edges, is there any black dust around the pulleys this could indicate that the belt is running to loose. The belt tension should be about ½ an inch in the longest side, more than this and it should be tensioned.   


The Alternator pulley is the only pulley that may be adjusted, the lower bolt enables the Alternator to swivel with a securing bolt and slide bar on the other two corners. The securing bolt and swivel should be eased enabling the Alternator to be pushed outwards,

 usually with the assistance of a hammer shaft as a lever. With the tension on the slide may be tightened and the other two securing bolts tightened.


Oil check, using the dip stick, found on the side of the engine. Remove the stick wipe and replace, remove and check the oil level. Two marks identify the low level and high level of oil. The difference between the two level marks is about a litre of oil. Therefore provided the oil is not on the lower mark and is more than half the distance would be considered as good. Over filling the oil can cause oil and oil fumes to be forced through the engine breathers causing oil smell about the engine. Not filling or allowing the oil to go below the marks can cause an engine to over heat and seize.


Engine coolant is needed to circulate around the engine maintaining the engine at its optimal working temperature. At this temperature all the working parts have expanded with the heat of the engine and therefore need to be kept at this position, not to cool and not to hot. The water pump driven by the fan belt keeps the coolant circulating through a thermostat which controls the release of the right amount of coolant necessary.


Coolant level may be checked either by a visual look at the coolant bottle, which is usually placed above the engine so the fluid siphons into the engine as required. Level marks on the container identify if more is required. Alternatively if the bottle is not present or an older engine the level may be checked by taking the radiator cap off the top of the engine and placing a finger into the hole, if it comes out wet up to the first knuckle then there is sufficient water in the tank, less then it will need to be topped up. Only do this when the engine is cold.


Sea water Impeller, sea cock and water filter are necessary to keep the engine coolant cool. The sea cock allows water into the boat, this salt water needs to go through a filter to make sure any bits of sea weed are not released into the engine, this water is then sucked in by the impellor which is rotating at three times faster than the engine and pumped through an anti siphon device, this device prevents the sea water from continuously running when the engine is stopped. From here, the cold salt water, goes through the heat exchanger which is a series of copper tubes placed in the flow of the engine coolant. Thus keeping the engine coolant cool and not contaminating it with salt water. Salt water is very corrosive especially around machined parts of an engine thus the reason we do not use salt water as a direct coolant.


Visual check of the sea cock and water impeller housing for leaks, usually show up as a white compound around the housing. This is the salt water leaking out and drying on the engine surface. If this is found it should be washed off with fresh water and the Impeller cover plate gasket checked and re sealed. The impeller should be changed annually, see engine service tips. 


The salt water filter check is to remove the sealing cap and take the inner basket out of the filter. This needs to be cleaned of any sea weed or bits found in it. The re assembly needs caution as all t

he parts are close fitting and only go one way, therefore if the basket is not seating flat or is protruding it is not in the right place. The cap should not be over tightened but should go on easy and just needs nipping up. If this is not done correctly a seal is not formed and the cooling water will not run through the engine. A good tip is if you have taken apart the filter then squirt a small amount of washing up liquid into the filter before screwing the cap into place. When you turn the engine on the cooling water exits through the exhaust you will witness frothy washing up liquid. Thus proving you have sea water cooling going on through the engine.    


The anti siphon device is a visual check, if you can see evidence of salt water leaking then be suspicious that the device is not working. In the worst case it allows sea water to continue to flow after the engine is stopped. This water can fill up the exhaust system and then back fill into the engine cylinders via the exhaust valves.


Whilst in the engine compartment it is worth checking the gear box oil level, this usually is not a problem but because there is not a lot of oil in the gear box any loss can be catastrophic.


The gear box dip stick is also the filler cap, remove the filler cap and wipe the stick, replace the cap without screwing it into place, remove and check the oil level, top up as required. You will notice a distinct smell about the gear box oil that is easily remembered. The oil is synthetic and is developed for use in gear boxes, high pressure close working environment.


For more information see Engine service. 
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                                                                                                                                                                                                                                                                                      GT Yachting October 2012