Diesel fuel is far different from gasoline. With gas, you pretty much put it in the tank and forget it, or you could in the days before E-10. Diesel fuel requires some management or you will suffer from the effects of poor quality fuel. Understanding the major differences goes a long way in helping to avoid fuel quality problems.
Diesel fuel is a fuel oil that is subject to contamination by both dirt and moisture from poor handling practices, leaks in piping, moisture condensing on the interior walls of tanks at the refiner, the distributor, your marina or retailer and in your boat. Microbial growth occurs in diesel fuel in the form of bacteria and algae that seem to thrive in the presence of water.
Water or moisture droplets in fuel will cause mechanical problems with pumps and injectors and will cause corrosion in the lines and fuel handling parts (distribution pump and injectors) of the fuel system.
A lot of moisture is introduced into diesel from the tanks the fuel is stored in. Every tank has this potential, but a boat’s fuel tanks are vented to the atmosphere. As fuel is used, the volume used is replaced by air drawn in through the tanks vent line. The vent is frequently about 3 ft. above the water line, so any air drawn in the vent line is going to be moisture laden. Then as temperatures fall in the evening and rise during the day, the fuel tank will condense moisture on the tank walls in the space above the fuel remaining in the tanks. As droplets form, they will run down and into the fuel. Since water is heavier than the fuel, it accumulates on the bottom of the tank.
Microbial growth in the diesel fuel is then possible since water is present to feed the growth. The growth seen in diesel is most often long stringy clumps of dark green or black crud that often will adhere to the tank walls and bottom. Sloshing around when the boat is in motion often breaks the microbial clumps off wherever it is adhered so it can then make its way to the filter system. It doesn’t take much to clog up a set of Racors.
Virtually all boats have dual fuel filtration systems. A primary filter, usually a Racor brand turbine filter, will be located between the tank and the engine. The design if the Racor is such that it will separate water from the fuel and collect it in a bowl at the bottom of the filter housing before it traps any dirt particle larger then the trap size of the filter element. Most Racor primary filters are available in 2 micron, 10 micron and 30 micron trap sizes. Another or secondary filter is located after the Racor, usually on the engine itself and most frequently supplied by the engine maker for his particular engine. Some manufacturers publish the trap size of their filters, some do not, but generally they are 2-5 micron filters.
Cold weather brings on other problems with fuel since diesel fuel will not flow in extremely cold conditions. It can gel or form wax crystals in the filters and plug them which stops fuel flow. Most fuel refiners formulate their fuels for cold weather use by mixing no.1 diesel (lighter, less viscous) with no. 2 diesel to yield a blend that does not gel in the climate area in which it is to be sold. This is not a major concern to pleasure boaters because we don’t usually go boating when the temperatures are cold enough for fuel to gel.
Bulk storage tanks and fuel handling between the refinery and the fuel fill on the boat are beyond the control of the individual retail fuel consumer. However, we can insulate ourselves from some of the inherited fuel handling and management problems with a few simple steps.
1. Try to buy your fuel from the same high volume retailer all the time. A high volume seller will cycle his tanks more frequently and the less time the fuel sits in a tank, the less water will be condensed in it. The less water the fuel contains means less chance of also having a load of sludge (fungus/algae/microbial growth/etc) in it.
2. Buy from a retailer whose pumps have a filter visible at the nozzle, and look for a date stamp date hand written on the filter body.
3. Keep your fuel tanks as full as possible to minimize the air space above the fuel in the tank.
4. Use a biocide in your tanks on a regular or maintenance basis to kill or prevent microbial growth in your tanks.
5. Use a multi-purpose diesel fuel additive on a regular basis. Look on the label for these attributes:
i. Contains no alcohol
ii. Disperses moisture
iii. Raises cetane levels
iv. Stabilizes stored fuels
v. Cleans injectors
vi. Reduces soot and smoke
vii. USLD compliant
viii. Add lubricity
ix. Protects against harmful effects of LSD and ULSD
Suggested additives for microbial growth control are:
1.Power Service Bio Kleen Diesel Fuel Biocide
2.Racor Diesel Biocide
3.Hammonds Biobor JF Marine and Jet Fuel Microbiocide
Suggested Multi-purpose general diesel fuel additives are:
1.Stanadyne Performance Formula
2.Power Service Diesel Kleen + Cetane Boost
There are now 3 different types of diesel fuel in the US. Off-Road high sulfur w/ more than 500 ppm sulfur; low sulfur diesel (LSD) with less than 500 ppm sulfur, and ultra low sulfur diesel (ULSD) containing less than 15 ppm sulfur. While it may be possible to have either off road or LSD at your marina, the truth of the matter is that there is only one normal diesel fuel distribution network and unless your area has a huge demand for off road fuel requiring additional and separate tanks and pumps, all fuel distributed now is most likely ULSD, and we are most likely now receiving ultra low sulfur diesel at almost all distribution points for pleasure boaters.
The process of removing sulfur also reduces the normal lubricity and reduces the cetane level in diesel fuel. Low cetane leads to hard starting and lower overall economy. Lower lubricity can have serious and expensive consequences on fuel pumps and injectors since the fuel passing through them is what lubricates them. Any diesel engine made prior to about 2003 can develop problems with ULSD. Check with your engine maker to be sure how to handle ULSD.
A good additive to handle the reduced lubricity in fuel is:
Stanadyne Lubricity Formula
1.Learn how diesel systems get contaminated and avoid introducing moisture or trash into your tanks.
2. Buy your fuel from the same high volume retailer who has and maintains filters on his diesel pumps
3. Use an anti-microbial additive like those suggested on a regular basis.
4. Use a general purpose diesel additive with the attributes listed above on a regular basis.
5.“Regular Basis” means every time you add fuel, you add the appropriate amount of biocide and general purpose additive.
6.Use a lubricity additive in your fuel.
I’ve got problems with dirty fuel —Now What Do I Do?
At some point, if you own a diesel boat long enough, you will experience an engine slowing down, dying or failing to turn up desired RPM due to a clogged primary filter. Always carry several extra fuel filters on your boat and know the proper way to change them. Do what is necessary to get back to your dock or a friendly place to tie up since it is a lot easier to deal with a dirty fuel system when you are secured to a dock than bouncing around in some slop somewhere.
First, try to clean up the system chemically. Do this by adding 10 oz. of Power Service Bio Kleen Diesel Fuel Biocide for each 200 gal of tank capacity.
This is a “shock” quantity of biocide and it will kill everything growing in your tanks and will cause the microbial chains to release and break off the tank walls and bottom and become suspended in the fuel. Now add one 80 oz. jug of Power Service Diesel 9-1-1 (red container)
for each 200 gallons of tank capacity. Next, go run the boat in some seas that will agitate the fuel in the tanks. The Diesel 9-1-1 has the unique attribute of being able to break up the chains of microbial growth into particles small enough that they will mostly pass thru a 30 micron filter. The secondary filter will catch some and the remaining particles are so small that they will pass through the fuel system and burn in the cylinders and pass on out as exhaust.
After approximately 5 hours of running time, the final clean up step is to change all the primary and secondary filters again.
If the above additives don’t clean up the system and you are still clogging filters, your only other alternative is to call a fuel cleaning service who will come to the boat and polish the fuel in the tanks for you.