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Fuelling Your Investment

Charlson Smith

This year marks the 120th anniversary of the ingenious inception of Dr. Rudolf Diesel’s eponymous creation, and few inventions of similar vintage can claim credit for markedly improving the quality of life of the globe’s population.  The compression-ignition engine would soon take the place of power wrought through the arduous and equally perilous tasks of shovelling coal, stoking fires, and managing explosion-prone high pressure boilers; with the exception of larger ships and powerplants, the diesel engine’s remarkably high thermal efficiency would ensure that it expeditiously supplanted steam power in many applications. 

The rapid dieselization of most railways and the widespread acceptance of the diesel engine on many waterways during the first half of the twentieth century is undoubtedly a testament to the reliability and ruggedness of the engine’s basic design and operating principles, however there are a few ways in which this mechanical marvel can be swiftly and efficaciously rendered useless.  Just as servicing a diesel engine with low quality oil will significantly shorten the engine’s lifecycle, providing poor quality fuel to an engine will prove detrimental to both its performance and reliability.  

It’s well-known that today’s modern high-speed diesel engines build fuel pressure on the order of several thousand pounds per square inch (PSI); in fact, many common rail engines routinely develop fuel pressures exceeding twenty-thousand PSI in some parts of the fuel system. Relatively high pressure fuel systems are nothing new to diesel engines, but it should be noted that regardless of the manufacturer or model, accurately pumping, metering, and injecting fuel at these astronomical pressures requires an incredibly high degree of precision in machining and manufacturing pumps, lines, and injectors. 

Cat Fuel2Over time, the space in which this fuel is injected has changed nearly as dramatically as the pressures at which it is injected.  Production of precombustion chamber engines for most manufacturers (including Caterpillar) is largely a not-so-distant memory, but nonetheless, more fuel efficient direct-injected engines have taken the place of their fabled brethren.  Higher injection pressures and advanced piston crown designs have obviated the need for the precombustion chamber, but the subsequent direct-injection engine design requires fuel of high quality and is more susceptible to performance issues caused by fuels with inferior properties.  A particular engine might feature a distributor pump, jerk pump, unit injectors, or a common rail, but it invariably requires clean fuel in order to fulfil owner and operator expectations. Thankfully, there are several sound, yet basic, fundamental practices that will all but eliminate complications stemming from fuel issues.  

Below are a few universally accepted guidelines that facilitate the clean delivery of fuel to marine engines. 

– Request a sample of the fuel to be taken on board from the supplier, and watch the sample being drawn from the tank.  If the fuel is particularly foul, sediment and water will sometimes be apparent by looking through the jar, glass, or test tube, etc., even at this early stage.  If no contaminants are seen, use a thermohydrometer to test the specific gravity according to the API (American Petroleum Institute) scale.  Caterpillar recommends using diesel fuel with a rating of 35 (or 35 degrees API), as using lighter fuels with lower specific gravities (meaning higher API ratings – the relationship is inverse) will not allow the engine to deliver its advertised horsepower. Remember to use the “thermo-“portion of the thermohydrometer and consult an API correction chart if the fuel is warmer or cooler than 60 degrees Fahrenheit (15.5 degrees Celsius)!  If the fuel is deemed acceptable, a first line of defence from contamination is a 100-micron fuel filter funnel available from many popular marine retailers.  Not only are these sub-$30 devices an extremely inexpensive insurance against polluted fuel, but they allow the individual fuelling the vessel to see if the filler neck is being overwhelmed with diesel which could possibly cause a costly spill, stain teak and paint, create a slippery deck, and most importantly cause environmental harm.

–Nearly all diesel fuel has at least a small amount of water dissolved in it, but it’s important to ensure there’s not an excessive amount waiting to cause damage in the engine’s fuel system.  Diesel can only contain a certain concentration of water, and this proportion changes with the fuel’s temperature.  As an example, fuel at 65 degrees Fahrenheit (18 degrees Celsius) might have 100 ppm water content, while the same fuel at 40 degrees Fahrenheit (4 degrees Celsius) might expel 70 ppm of that water and disperse it into the fuel, leaving only 30 ppm suspended in the diesel fuel (Caterpillar, Inc. Diesel Fuels and Your Engine (SEBD0717-04). Peoria: Caterpillar, Inc., 2004). 

While the water in the diesel might not be visible to the naked eye, it’s still important to have adequate filtration measures in place to ensure that even small amounts of water are not allowed to reach the fuel pump.  Aside from wreaking havoc in the high-pressure fuel system, water that does pass through the pump and is injected into the cylinders will rapidly vaporize and could damage the fuel injectors leading to a host of other complications stemming from overfuelling.  Using a high-quality sediment-type filter setup ensures that if there is water or algae (referenced later) in the fuel, it will be quickly detected by the observant captain or engineer.  Sediment-type filters are often installed in double, triple, or sometimes quadruple setups and most feature glass bowls at their base, making them (and the contaminants they catch) easily identifiable. 

Cat fuel 2Care should be taken to ensure that only one filter is operating at any one time to eliminate the possibility of filters running, and consequently fouling, simultaneously; this would result in the engine having to be shut down in order for the filters to be serviced.  Rather, only operate one filter (or two, in the case of a triple or quadruple setup) at a time so that the engine may draw from the alternative filter while the fouled filter is replaced or cleared.  Another popular setup includes using two banks of filters (primary and secondary) with the former featuring a 10-micron filter and the latter incorporating a 2-micron filter.  Employing this setup gives the engine a tertiary line of defence in the form of the on-engine spin-on filter, which should be replaced per the operation and maintenance manual included with the engine.  Cat® high-efficiency spin-on fuel filters are easy to service and are readily available, however it is important to follow installation instructions included with the engine; do not pre-fill these filters with diesel to avoid having to prime the fuel system, as this unfiltered fuel will flow into the fuel pump and could cause damage.  Always prime the fuel system according to the operation and maintenance manual.  

–Algae (bacteria) growth in diesel fuel is a phenomenon that unfortunately is not uncommon in a marine environment.  Two conclusions may be drawn when algae is detected: one, there is water in the fuel; algae cannot grow in diesel without the presence of water, and often the algae blossoms at the boundary between water and diesel. Two, the problem must be quickly addressed, as algae will promptly fill the glass bowls on sediment filters and plug the paper elements.  Although the use of a diesel-soluble biocide will alleviate many problems resulting from algae growth, samples should be taken from the lowest part of the fuel tanks in order to ascertain the amount of algae and water in the tank.  Needless to say, that fuel from the bottom of the tank should be removed and the fuel tank re-checked to ensure all contaminants have been removed.  

–As temperatures further decrease, the fuel will encounter its cloud point, below which the paraffins contained within the fuel begin to congeal or become waxy.  Lighter fuels typically have a lower cloud point. However, as stated before, Caterpillar recommends No. 2 diesel fuel for all engines as lighter grade fuel oils usually do not have the required lubricity necessary for continued reliable engine operation.  Fuel heaters can be used to overcome high cloud (or in extreme cases, pour) points and should be employed in order to prevent ice crystals from obstructing fuel filters.  

Engines today that run on low- and ultra-low sulphur diesel are particularly susceptible to contaminants, as the refining process known as hydro-treatment removes not only the environmentally harmful sulphur but also other components that add to the fuel’s lubricity.  Although many refiners add compounds to remedy this loss of lubricity, it is still of paramount importance to ensure fuel is free of contaminants, blended to a suitable specific gravity, and is maintained at a useable temperature. This, along with conducting recommended maintenance at recommended intervals, owners and operators can expect a long and profitable life from their engines.


Growing up in the Gulf Coast town of Pass Christian, Mississippi, Charlson Smith has been a mariner all of his life.  While on summer break from the University of Mississippi, he would spend his time operating a 65’ Donzi sportfisher out of New Orleans, Lousiana, the coast of Mississippi, and Port Everglades, Florida. Upon earning his MBA from Ole Miss, Charlson joined Caterpillar Marine Power Systems as a marketing representative.  His office is at the Marine Center of Excellence in Greenville, South Carolina.  He can be reached at or (864) 370-6505.

For more than 85 years, Caterpillar Inc. has been making progress possible and driving positive and sustainable change on every continent. With 2011 sales and revenues of $60.138 billion, Caterpillar is the world’s leading manufacturer of construction and mining equipment, diesel and natural gas engines, industrial gas turbines and diesel-electric locomotives. The company also is a leading services provider through Caterpillar Financial Services, Caterpillar Remanufacturing Services, Caterpillar Logistics Services and Progress Rail Services.

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