Fuel Consumption – How is it measured



One of the primary considerations when choosing an engine is fuel consumption. Different engines manufactured by different companies all consume fuel at different rates. However, when you add power, climate, metering methods and technology, maintenance, and other factors into the equation, the answer might not seem so straight forward.

Brake Specific Fuel Consumption (BSFC) is the best way to determine fuel consumption between engines. It is the ratio of fuel consumed to power produced.

For example, on the MarineDiesel VGT500, at full load, 3,600 RPM, the engine consumes 230 g/kWh of diesel. However, at different loads and different RPM levels, the engine will consume a different amount of fuel. That is why when you see BSFC numbers, the engine speed is always listed, and it is important to look at the fuel consumption curve provided by the manufacturer (if they do so).

When things get complicated is that, though BFSC, g/kWh is generally the standard, often engine makers will show fuel consumption in imperial units, or as simply a flow rate, as in l/h or gal/h. This does not take into account the engine power, but merely a rate based upon time. In order to truly compare engines and performance, the BSFC is a must.

Generally, fuel consumption rates for marine engines in the same class as the VGT series will show BSFC rangine from 200 to 240 g/kWh, depending on the maker. Gasoline powered engines typically have far higher consumption rates than diesel engines.

It is also important to recognize that fuel consumption is greatly impacted by maintenance (or lack thereof), climate, operating conditions, fuel quality, and engine compression (set by the ECU). Maintaining the engine according to the manufacturer’s recommendations and oprating within the designed parameters can greatly reduce fuel consumption over the long term.


Maintenance Tip of the Week – Check Levels 04/28/2014


Maintenance Tip of the Week


Before starting the engine always check the oil and coolant level. . Also inspect that no leaks on oil-, fuel- or cooling systems are evident.

MarineDiesel manuals now available on Amazon.com



MarineDiesel is pleased to make our manuals for marine engines downloadable on Amazon.com for our customers’ use.

MarineDiesel Publications on Amazon.com


There is a small charge for downloading the manuals from Amazon, properly formatted to work with your device. This is required for listing in the Amazon store (We will always make a PDF, along with a printed copy to all customers free of charge.)

However, for MarineDiesel customers, we recognize the utility of having the manual in an easy to read format on your devices (Nobody drags thir desktop with them into an engine room), so we will credit the amount you pay for the downloaded manuals into your MarineDiesel account for future purchases of spares or services.

We hope you find this useful and we welcome any customer feedback!

Ask Professor Diesel 04/28/2014 – Engine Noise


This week’s question comes from Ibrahim in Indonesia about engine noise

Dear Professor Diesel:

We installed your MD170 engines two years ago, and they have been working great. However, recently, they seem to be very noisy. Is this normal? Are there ways to correct the problem?


Engines can get noisier over time, especially with heavy use. The reasons why can come from a variety of sources:

  1. Vibration over time loosens bolts, fasteners, and belts
  2. Fuel and oil filters have not been changed according to the schedule listed in your manual, or you have been operating with dirty fuel
  3. The engines are using the wrong fuel
  4. Oil has not been changed
  5. The engine timing is off
  6. The injectors are dirty

With the limited information you provided, it sounds as if your engine is ready for overhaul. How long has it been since this was done? If the engine was recently overhauled and mechanical causes can be eliminated, a variety of noise reducing methods are available, such as:

  1. Insulating the exhaust.
  2. Adding silencers.
  3. Changing the exhaust configuration.


If you have a question you would like to ask Professor Diesel, simply fill in the form below:


[accua-form fid=”9″]




Maintenance Tip of the Week – Serial Number 04/21/2014


Maintenance Tip of the Week


When you need to contact MarineDiesel about a warranty or other maintenance issue, you will need to provide us the engine’s serial number. The Marinediesel engine has a stainless steel serial number tag located on the starboard side of the engine. This serial number tag will reflect the engines six digit serial number starting with MD-XXX######.

What is torque?



Webster’s defines torque as:  a force that produces or tends to produce rotation or torsion <an automobile engine delivers torque to the drive shaft>; also:  a measure of the effectiveness of such a force that consists of the product of the force and the perpendicular distance from the line of action of the force to the axis of rotation.

Engine makers often highlight the amount of torque their engines provide. Why?

Since torque measures rotational force, and internal combustion engines produce rotational force via a camshaft, torque measures how much force is actually generated through the flywheel, rather than the force of the pistons in the cylinder.

Quite simply, torque is often a far more useful measurement or indicator of an engine’s performance. In other words, it can be easier to explain thusly: Whereas horsepower measures power, torque measures the amount of work that an engine can perform.

Torque is measured in Newton Meters, Nm, and is determined via testing on a dynamometer.

Diesel engines produce usable torque only at a limited range of rotational speeds. The amount of torque produced at any one point on the curve can vary significantly between one engine and another. This is why torque is more useful to engine buyers than merely horsepower. Torque measures the work an engine can perform.

To illustrate, take two 500 hp engines, one mounted on a small tugboat, and one mounted on a racing boat. Both engines produce 500 hp, but the tugboat needs far more torque in order to pull a heavy load, at far slower speed than the racing boat that needs a rapid accelleration and maintaining a high speed.

This is why careful examination of the torque curves is critical when choosing an engine. All power is not created equal.

What is horsepower?



When shopping for engines, many people start by comparing the horsepower ratings of different engines. What does the term horsepower really mean? In the late 18th century, James Watt, one of the early pioneers of the steam engine, coined the term “horsepower” in an attempt to show the power output of steam engines in a way that the common man could easily understand: This engine provides the power equivalent to the power produced by ___  draft horses pulling a plow, sledge, or wagon. As a marketing tool, this example was ideal. Watt was able to sell his engines, becoming successful over the years.

Though revolutionary at the time, the use of horsepower as a term of measurement quickly showed the inherrent problem with the unit: it varied based on location, or who was making the calculations. How much can a horse pull? Old horse? Young horse? Strong horse? Weak horse? Pulling for how long of a period?

Over the years, the watt really became the standard of measurement of power, and its’ use is mandated in the EU by law, with horsepower being permitted only as a supplementary, or marketing, standard. Since MarineDiesel manufactures in Sweden, part of the EU, we comply with this standard and all of our engines are rated based on kW. SAE determines the standards for measuring horsepower, and though we are not required to comply, MarineDiesel complies with all of these standards, giving consumers reliable, tested, and verified measurements of engine power.

Regarding horsepower and marine engines, there are four terms a buyer will hear:

Mechanical Horsepower (hp)

1 hp = 746 W

Metric Horsepower (mhp)

1 mhp = 735 W

Brake Horsepower (bhp)

Brake howsepower is often used by engine manufacturers since it refers to the raw power of the engine withoug the loss experienced through gearboxes, alternators, electrical systems, etc. It is determined by putting the engine in a dynamometer and measuring the power, without loss producing components connected. When comparing engines, this measure is most useful in giving an “apples to apples” comparison.

Shaft Horsepower (shp)

This is a measurement of power provided to the vessel shaft, after the geabox losses have been taken into account, and is determined by measurement. Think of shp as “usable” power.

Maintenance Tip of the Week – Fuel 04/14/2014


Maintenance Tip of the Week


Always remember to bleed the fuel line when changing fuel filters. Air in the fuel line will shut down the engine and this fault is easily prevented.

Dirty Fuel



MarineDiesel’s marine engines are extremely reliable when maintained according to the maintenance schedule detailed in the owner’s manual. However, no engine, regardless of manufacturer, is reliable unless proper care and maintenance is performed regularly. We warranty our products against manufacturing defects, yet, there are always instances where the engines are used in ways never intended, or under conditions that would destroy any engine.

Over 50% of our customers’ mechanical issues come from a single source:


The use of poor quality fuel can be incredibly damaging to modern diesel engines.

Diesel engines manufactured today must comply with strict emissions standards that are emerging globally, but particularly in the EU and USA. Prior to these emissions standards being enacted, dirty fuel was rarely a problem. Indeed, excess carbon or rust would simply be burned in the combustion process. Indeed, on some old, low RPM, two stroke engines, these contaminants could actually be beneficial to the engine.

That is no longer the case.

High performance marine engines require clean, high grade fuel in order to operate properly, and comply with emissions regulations. Unfortunately, the world is not a perfect place, and there are many regions where high-quality fuel is the exception, rather than the norm.

  • Rust, adulteration (water, paraffin), misgraded fuel (intentional or unintentional) are all common problems. In some remote or developing regions, sometimes the assumption to make is that the fuel is contaminated.
  • We have seen owners delay replacing fuel filters as a cost savings measure (far more expensive in the long term)
  • We have seen people running without filters
  • We have seen filters improperly installed
  • We have seen additives that are magically supposed to reduce consumption

All of these factors greatly reduce the service life and reliability of the engine. They also hamper performance more than just about any other factor. The use of high quality filters (Racor or OEM), changed correctly and when needed, is a simple solution that is often overlooked.


Maintenance Tip of the Week – Heat Exchanger 04/07/2014


Maintenance tip of the Week


Heat exchanger maintenance is a complex task, normally best performed by MarineDiesel factory trained dealers and distributors. This maintenance should not be ignored, as the internal parts of the heat exchanger can corrode over time, in addition to the fact that they are often stepped on and damaged in cramped engine compartments.