You can change your marine diesel engine oil yourself by following these instructions.

Use only a Marine Diesel Engine Oil of good quality.

  • 5 liter and 10 liter drums are easy to use and can be refilled with old oil for correct disposal.
  • Change your oil and filter at least every 100 hours. Keep spare oil filters on board at ALL times.

Many old marine engines use a lot of oil and will require plenty of spare oil for long passages.

  • For good engines—Straight 30 W.
  • For worn engines—Straight 50 W.

Always keep plenty of rags, degreaser and oil-absorbent materials on board your boat. This is a messy job. Always clean engine and bilge after oil/fuel filter changes.

Always run a marine engine for about 10 minutes before oil change to heat oil or you will not be able to pump it out, even with a good quality oil sump pump.

Some Fuel Injection Pumps have sumps with engine oil (e.g. Lucas & Sims); this must be changed at the same time as diesel leaks back and dilutes fuel and reduces viscosity—oil level then goes up. This can happen to engine sump on some marine engines with internal return lines.

Removing Filters: Cut open 2 liter milk container, hold beneath filter, remove filter and drop into container, then place this container into a bucket with rag in the bottom. This system will save you some time in cleaning.

Use the same method for fuel filters.

Fitting filters: Smear oil on rubber seal before fitting. Do not fit too tightly

  • If possible, fill filter with oil before fitting.
  • Check filter is not leaking and oil level is correct after a momentary run.

Many thanks to Laurence Burgin for this brief outline of changing your marine diesel engine oil. A full description is included in Laurence’s e-book Marine Diesel Engine Basics now available for download from Amazon.

Fresh water circulated through the engine jacket is cooled by seawater pumped through a heat exchanger. The seawater is discharged overboard either through the exhaust or directly over the side of the vessel. If discharged through the exhaust, it is known as a wet marine exhaust system.

The water is injected into the exhaust system, usually in the form of an injection bend fitted immediately after the manifold. In most cases all the raw water flow is taken by the exhaust but in cases where this results in excessive back pressure, the amount of water injected into the exhaust can be reduced and the remainder piped overboard.

A wet marine exhaust system has the following advantages:

  • The exhaust pipe is cool enough to be made of uninsulated fiberglass reinforced plastic (FRP) or rubber.
  • The use of a flexible exhaust pipe more easily accommodates the movement of the engine when running.
  • the wet exhaust is quieter than the dry marine exhaust due to the silencing effect of the water.
  • The wet marine exhaust line is particularly suitable with a flexible mounted engine because it can mostly be made of oil-and-heat resistant rubber exhaust hose.

Many types of mixers, silencers and mufflers are available, which should be fitted only in consultation with the marine engine manufacturer. The design of the wet exhaust system must be such that water cannot run back or siphon into the engine when it is at rest (even when subjected to violent motion such as at an exposed anchorage).

Engines installed with cylinder heads below the waterline are more vulnerable. Therefore, an anti-siphon valve (vacuum breaking device) is fitted on their exhaust cooling line, which helps prevent water siphoning back into the engine.

… from Australian Boating Manual

Bleeding The Fuel System in a Marine Diesel Engine

To bleed the fuel system, or part thereof, means to remove all the air from the fuel lines and chambers in the system. This is done by pumping fuel through the lines and venting the air/fuel from various bleed points in the system.

Click Here For Marine Diesel Engine Workshop Manual

A fuel system will need to be bled after changing the fuel filters, running out of fuel, if there is water in the fuel, if there are loose connections causing air leaks, if you have taken on poor quality fuel, or if there is bacterial growth in the marine diesel fuel tanks.

Always follow the correct progression of bleeding as shown in the diagram. To pump the fuel you must first operate the lift pump to bleed the low pressure side of the system. The lift pump must be pumped many times to ensure complete bleeding. Ensure your lift pump works well. Aftermarket bleeding pumps can be fitted.

fuel system schematics

If pump does not operate (that is, the lever is slack), check if rocker arm is depressed. Turn engine over and try again.

First bleed primary filter by loosening bleed screw on top of housing. Holding a container under filter, pump fuel until no bubbles are visible and fuel is running freely (that means it’s going everywhere!). Tighten bleed screw whilst pumping. Repeat process on engine filter and fuel injection pump. Put throttle wide open in neutral and crank over engine for 25 seconds. If engine won’t start, crack one or more injectors until fuel leaks out, then tighten whilst cranking over engine. If engine still won’t start, repeat entire bleeding process.

Have plenty of rags and fuel clean-up equipment on hand. This is a messy job!


Marine Diesel Lubricating Oils

The marine engine lubricating oil does not merely lubricate the moving parts, it also performs a number of specific functions.

1 It forms a film between the moving parts, preventing metal-to-metal contact. As a result, wear is kept to a minimum, power loss due to friction is minimized and engine noise is kept to a low level.

2 It acts as a cooling agent by carrying heat away from hot engine parts.

3 It forms a seal between the piston rings and the cylinder walls.

4 It acts as a cleaning agent.

5 It resists the corrosion of highly-polished engine surfaces by the acidic products of combustion that enter the sump past the piston rings.

Click Here For Your Marine Diesel Engine Shop Manual

To efficiently fulfill these requirements the marine lubricating oil must posses a number of important properties. Of these, viscosity is one of the most important, and has already been defined as the reluctance of a fluid to flow. A fluid with high viscosity may be said to be thick or heavy, while a fluid with low viscosity is said to be thin, or light. Fluids tend to become less viscous as they are heated and, conversely, to become more viscous when cold. An engine oil must not become so thick in winter as to cause starting difficulties, but must not become so thin at operating temperatures as to fail in its requirements as a lubricant.

Because deposits and acids are formed through the combustion of fuel, and the marine engine oil should have the ability to wash the deposits from engine components and to neutralize the acids. The oil should not foam when agitated in the sump and should be able to withstand the extreme pressures encountered between certain engine components.

Mineral oil, by itself, cannot fulfill all the requirements of an engine lubricating oil, and certain chemicals are added it.

In the example at right, oil is pumped by a positive displacement pump which is driven by the engine to circulate the oil through the system.

Alternatively, some old engines are splash type where oil is thrown around the sump by the crankshaft scoops.

You can find a ton of information on marine diesel engines in the downloadable e-book from Amazon Marine Diesel Engine Basics. You can print out your own copy, insert the pages into plastic covers and take it with you when you work on your engine. It is a highly recommended book. Buy your copy now!

Marine Diesel Fuel Is Your Marine Engine’s Lifeblood … Good Fuel (Blood) = Healthy Engine

  • Always keep an eye on the condition and color of your fuel.
  • Fuel tanks must be clean and full.
  • Always have one (preferably twin) primary fuel filter / water trap and an engine filter / water trap.
  • Primary fuel filters should be changed regularly—same time as oil change, every 100 hours.
  • Secondary filters may not require changing as frequently.
  • Some engine filters can be replaced with an after market fuel filter / water trap unit.
  • Keep at least two spare fuel filters in a plastic bag and stored in a clean dry place.
  • Use only high quality fuel lines. They must be clean, internally and externally, and easily removable. They must have quality twin hose clamps at each join.
  • Water traps / filters must be easily visible and serviceable. Check glass regularly for water, drain off any water from base of bowl by loosening the drain plug whilst holding cup underneath.
  • Bleeding may not be necessary after this process.
  • The primary fuel / water trap should preferably be located below the level of the fuel tank to allow gravity bleeding after primary filter change, eliminating the need to pump bleed.
  • Always use fuel conditioner / biocide, to prevent algal growth in fuel. Add at each refuelling.
  • Old fuel tanks: Many are contaminated and should be replaced or chemically cleaned.
  • Poor fuel and water will cause expensive damage to your fuel pump and injectors.
  • Fuel tanks should have correctly sized fillers and breathers. The fuel pick-up should have a shutoff valve and, ideally, the tank will have a drain fitted lower than the pick-up. This drain can be used to fit a balance line with central drain. Ideally they should have inspection hatches for cleaning.
  • A balance line between multiple tanks helps balance the ship’s load.
  • Tanks should have baffles and be adequately secured.

This is an excerpt from Laurence Burgin’s acclaimed e-book Marine Diesel Engine Basics. This e-book is highly recommended for all marine diesel engine owners. Now available for immediate download from Amazon.


A conventional marine diesel engine produces power when hot compressed air ignites fuel sprayed under very high pressure into the cylinder head. A marine diesel engine does not require a carburetor to mix fuel and air or spark plugs to ignite the mixture. Instead it employs the pistons to compress the air to 3000 kPa which causes it to become extremely hot and the fuel is ignited as soon as it is injected into the cylinder.

Some marine diesel engines are fitted with a heater plugs in the inlet manifold or a glow plugs in the pre-combustion chamber of each cylinder to provide additional heat to the combustion air during starting.

Diesel engines are heavier and slower revving than petrol engines but they are also more reliable because they do not rely on external carburetion or an electrical spark for ignition.

Newer engines use an electronic fuel injection system whereby fuel and air are mixed more thoroughly in the pre-combustion chamber before entering the cylinder. This system maximizes power and fuel economy and is also less polluting.

Every boat owner should have an understanding of the regular marine diesel engine maintenance chores like changing the engine oil, replacing the water pump and checking fuel filters and lines.

An excellent guide for beginners is Laurence Burgin’s “Marine Diesel Engines for Beginners”. This handy downloadable e-book can be printed out, inserted in plastic sleeves and taken into the engine room with you when you are looking after your engine. It is well illustrated and contains easy-to-follow and well-written instructions on many aspects of marine diesel maintenance including:

  • Oil systems
  • Changing the engine oil
  • Exhaust systems
  • Tools you must carry for both inshore and offshore
  • Engine cooling systems
  • Electrical theory and systems
  • … and much more

Marine Diesel Engine Basics book cover

If your marine diesel engine fails to start it could be for any of the following reasons…

Engine does not turn over:

  • Totally flat battery
  • Battery connections or fuses
  • Faulty switches (battery and starting circuit)
  • Starter solenoid
  • Starter motor
  • Engine locked up –– water or oil in cylinder (or seized up)

Engine turns over but does not fire:

  • Fuel is shut off / no supply
  • Low cranking speed: engine in gear; auxiliary equipment engaged or low battery charge
  • Cold weather thickens the oil in the crankcase (turn the engine over a few times) also affects battery cranking efficiency
  • Engine in poor condition – low compression – too cold
  • Poor fuel injection
  • Check engine stop control has been reset
  • No air – emergency shut down stopping air (GM two strokes)
  • The pre heater (glow plugs) not operating
  • Air or water in fuel

Click Here For Marine Diesel Engine Maintenance For Beginners

Most reciprocating piston internal combustion engines work on one of two mechanical cycles—the four-stroke cycle or the two-stroke cycle. Marine diesel engines work in the same manner. The cycles designate, in correct sequence, the mechanical actions by which (a) the fuel and air gain access to the engine cylinder, (b) the gas pressure (due to combustion) is converted to power, and (c) the burnt gas is expelled from the engine cylinder.

Click Here For Basic Guide To Marine Diesel Engines

The basic four-stroke cycle marine diesel engine

From the name, it is obvious there are four strokes in one complete engine cycle. A stroke is the movement of the piston through the full length of the cylinder, and, since one such movement causes the crankshaft to rotate half a turn, it follows that there are two crankshaft revolutions in one complete engine cycle. The four strokes, in correct order, are:

  1. The inlet stroke. With the inlet valve open and the exhaust valve closed, the piston moves from top dead center (TDC) to bottom dead center (BDC), creating a low-pressure area in the cylinder. Clean, filtered are rushes through the open inlet valve to relieve this low-pressure area, and the cylinder fills with air.
  2. The compression stroke. With both valves closed, the piston moves from BDC to TDC, compressing the air. During this stroke the air becomes heated to a temperature sufficiently high to ignite the fuel.
  3. The power stroke. At approximately TDC, the fuel is injected, or sprayed, into the hot, compressed air, where it ignites, burns and expands. Both valves remain closed, and the pressure acts on the piston crown, forcing it down the cylinder from TDC to BDC.
  4. The exhaust stroke. At approximately BDC the exhaust valve opens and the piston starts to move from BDC to TDC, driving the burnt gas out of the cylinder through the open exhaust valve.

For more help with your marine diesel engine grab your copy of “Marine Diesel Engines For Beginners

Fuel injection is the way of the future, but not necessarily because of its power increasing capabilities! In fact, fuel injection itself does not add significant horsepower to the engine. Fuel spills can be harmful to the water, fish, or other wildlife common to the area. You should always obey any postings from the Department of Natural Resources regarding noise regulations and no-wake areas.

Click Here For Marine Diesel Engine Manual

Marine diesel fuel systems, cooling systems, lubricating systems, electrical systems, exhaust and intake systems, and more will all be explored and thoroughly explained in layman’s terms. Mechanical problems are almost always the result of some human weakness or deficiency, and you must have a boating survival plan.

Fuel expands as it warms, so fill only to 90% and fill up just before leaving on a trip. Use oil absorbent cloth to catch drips and overflows. Marine fuel, for engines or for stoves, is the most common component of boat fires or explosions. Leaks in systems and ventilation shortcomings are the usual problems. Fuel overflows from gas tanks are dangerous to people and toxic to fish and other marine life. The traditional method for determining if you have a full tank is to look for fuel spilled from the tank overflow vent.

Fuel spills are harmful to aquatic life as well as to boats. Exposing hulls to fuel spills will cause the hull finish to deteriorate.

Take a basic marine diesel engine course and learn how to keep your friends and family safe when boating. Find out how to service your marine diesel engine and know that it is properly maintained. Understand which marine diesel spares you must carry on board to make running repairs. Discover how to make emergency marine diesel repairs on the water.

Click Here For Downloadable Marine Engine Manual

Whether you are a weekend boater or a long-distance sailor you must be able to maintain your marine engine and make repairs when on the water. Lack of marine engine knowledge can lead to disaster!

So, if you want to understand your marine diesel engine … then please keep reading.

A couple of years ago I met shipwright Laurence Burgin when he was doing some work on my boat. Laurence is a shipwright with more than 20 years experience on a wide variety of vessels. He also teaches marine diesel engine maintenance for beginners at yacht clubs around Sydney.

I attended one of Laurence’s marine diesel maintenance courses and the knowledge I gained has enabled me to do much of the regular engine maintenance on my boat myself. I still get the service guy from the engine manufacturer to do some of the more complex maintenance but with what I can now do myself I’ve saved thousands of dollars in maintenance costs.

More importantly, I have confidence that I can handle an engine emergency out on the water!

Laurence’s marine diesel engine course is now available as a downloadable e-book through Amazon.