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Beefing up tropical light diesel fuel

Jan 1, 2003
From Ocean Navigator #124 September/October 2002

From Ocean Navigator #124 September/October 2002

To the editor: I read with great interest the recent article on diesel fuel quality and cleanliness ("Keeping it clean," Issue 121, Ocean Voyager 2002). All well said; in fact, probably the best said that I have seen. I would like to give another small piece of information to you from my lessons of hard learning.

For some years in Panama, I worked for the U.S. Army with the Directorate of Engineering and Housing, as a power systems repair inspector. This is a position of repair inspector of most anything that the Corps uses in heavy equipment, generators, installed systems, etc. My background for that came as a nuclear power plant operator/ mechanic with the U.S. Army.

To the point, we received a piece of heavy mobile equipment called a Kershaw land clearing machine, originally designed for clearing brush and small trees to five inches diameter in Vietnam. We put it to use clearing elephant grass and scrub areas for physical security around the military bases in Panama. This unit used a Caterpillar diesel engine that ran continuously at full rated speed/load coupled to hydraulic drives for propulsion, cutting heads, and life support systems for the operator (i.e., A/C and air filtration in a closed operator's cabin — lots of dust, dirt, and debris).

We placed the unit in service and after about 200 hours lost the fuel injection pump. Taking a close look at it indicated overheating, or water scoring, in the pump. Filters were checked and the change interval shortened by half and a new pump was installed. All went well for 300 or so hours and the pumped cooked again.

At my wits end, I took a sample of diesel and did the usual field tests (similar to the article's mason jar test) and found nothing out of order. We cut up the filters and could find nothing; the water separator was clean. So I pulled a couple of gallons of the diesel and sent it off to the Air Force fuels testing lab and awaited the results.

What an interesting result: the fuel was something between kerosene and No. 1 diesel. We contacted the local refinery that was supplying fuel to us and asked them for a sample of the milspec No. 2 diesel that we were buying from them under contract — you bet, the same stuff. With great wrath, the contracting division of supply, armed with our information, attacked. We found that in the tropics it is typical of the local refineries to go light on the fuel, as it is cheaper to make than the heavier fuels.

We cancelled the contract for fuel delivery and ordered No. 2 diesel fuel marine from the U.S. government supply system. In the mean time we came up with the following fix: add one quart of outboard (OB) motor oil to 100 gallons of the light diesel. This worked like a charm, with the added benefit that the additives of the OB oil helped prevent corrosion within areas that dried out while gear was sitting.

That takes us back to the lubricity issues with diesel and my experience with our boat Pogo II and its Westerbeke M60. We built Pogo II in 1978 and have operated her in the Panama/lower Caribbean area for most of that time. I used to lose fuel injectors on the engine every 300 to 400 hours until we discovered the above information about tropical diesel. At that point I started the one quart OB oil to 100 gallons of diesel as a religious maintenance issue on the operation of Pogo's engine.

Last year, after 14,000 hours of operation, I pulled the old Westerbeke. The injection pump and injectors were the same final rebuilds that I did in 1986 after my discovery of the light tropical diesel. More than 14 years and 8,000 hours or so with clean, lubricious diesel and no problems.

This is now something I recommend to all voyagers of the tropical latitudes. By the time most reach Panama they are looking for injector pump /injector rebuilds on engines with as little as 150 hours. I tell my tale, and so far have gotten no negative feedback from my disciples.

Craig Owings sails Pogo II, a CSY44 cutter, and writes from the Puerto Lucia Yacht Club in Salinas, Ecuador.

Steve C. D'Antonio responds:

Thank you for taking the time to comment on the article. Your real world experiences with less than perfect diesel fuel are very interesting and not unfamiliar. I've heard similar stories from other readers and customers of mine here at the boatyard.

Using two cycle outboard oil at the concentration you mentioned, one quart for every 100 gallons of fuel, would certainly improve the characteristics of light diesel or kerosene. In the mid-20th century it was not unusual for farmers to run diesel tractors on kerosene (in fact, some tractors of the day would run on diesel, kerosene or gasoline with only slight modifications, but they were all spark ignition) with the addition of a little crankcase oil. My only concern would be running additional oil in ordinary, heavy, No. 2 diesel. This could lead to coking, which is the buildup of carbon deposits on and within injector tips. I suppose that if you knew you were getting light diesel (there's really no way to determine this without a lab test) then this practice would be helpful. However, it's unnecessary with ordinary diesel and may actually lead to problems if over done. I'm not a chemist or a petroleum engineer; however, I doubt that at the concentration you mentioned, essentially 400 to 1, any real harm could be done and the benefits of additional lubrication seem obvious.