Proper Fuel for Cummins Engines
stabilized by the fuel supplier and there is a monitoring program in place. Periodic testing of
the engine is recommended to be performed frequently enough and long enough to make sure
that the fuel supply is replenished and stays fresh.
Duplex Fuel Filtration Systems
Stand-by and emergency generators can be called upon to run for hundreds of hours in case
of emergency. Such critical operations could possibly wish to install a duplex fuel filtration
system. These systems allow rapid switching to fresh fuel filters. It is recommended that such
service occur while the engine is shut down briefly. A Cummins® or Cummins Filtration™
Distributor can advise on the proper installation for a particular engine and location. Fuel Tank Care and Maintenance
Tank cleaning is a major operation which requires complete draining of the tank, and should
only be done by professionals. It is therefore carried out infrequently, normally on the schedule
of several years coinciding with (statutory) inspection and maintenance requirements. Good
housekeeping can help extend periods between tank cleanings.
Water bottom measurements can be made on an appropriate time interval (via automatic
gauging or regular tank dipping with water finding paste) and water can be removed when
necessary. This is important since any water and sediment can be stirred up when the tank is
filled. Cummins Inc. recommends waiting a minimum of one hour per foot of fuel depth before
dispensing fuel after a delivery. If water and sediment are observed, additional setting time is
one way of bringing the fuel back into specification.
It is virtually impossible to stop water from entering the supply chain; therefore, good
housekeeping is essential. Hardware, tanks, and pumping systems should be routinely
inspected and maintained. Fuel should be checked periodically for contamination by water to
ensure that there is no free water present in the fuel entering the engine, and dissolved
(emulsified) water does not exceed 200 ppm.
Cummins Inc. recommends that if the fuel does not meet the ISO 4406 cleanliness code of
18/16/13 in bulk storage, additional filtration be applied before the fuel is delivered to the
engine. A Cummins® or Cummins Filtration™ Distributor can supply hardware and additional
Common Issues With Winter Fuel
This section presents the various winter fuel issues and methods of dealing with them.
Two winter fuel handling issues, wax and ice, have annoyed diesel operators for years. There
is no solution to either of these problems that is ideal for all situations, but the better the
problem is understood, the less difficult the process of finding a solution becomes.
Determining whether a low power complaint is due to fuel filter plugging is fairly simple:
replace the fuel filter with a new filter. If this allows the vehicle to operate normally, even for a
short period of time, then obviously something in the fuel is plugging the filter and causing the
complaint. A simple way of determining whether the filter plugging is caused by wax or ice is
to bring the plugged filter into a warm shop, drain out the liquid fuel, place the filter upside
down on a piece of paper or in a shallow pan, and allow the filter to warm to room
temperature. If there is ice in the filter, it will melt and run out of the filter and the water on the
paper or in the pan will be obvious. Most petroleum wax, on the other hand, will not melt at
room temperature. To speed the analysis process, the filter can be cut open and spread out.
Once the cause of the low power complaint is determined, a logical solution can be chosen.
All middle (or intermediate) distillate fuels, such as jet fuels, heating fuels, and diesel fuels,
contain paraffin wax. Paraffin wax is a solid, crystalline mixture of straight-chain or normal
hydrocarbons melting in the approximate range of 40 to 60°C [104 to 140°F]. This paraffin wax
occurs naturally in the crude oil from which fuel oils are distilled. The wax content of a distillate
fuel varies greatly, depending on the crude oil from which the fuel is produced and in the processing of the fuel. Generally, higher boiling distillate fuels, such as U.S. Number 2-D
diesel fuel, have a higher concentration of paraffin wax than lower boiling distillate fuels, such
as jet fuel.
Because of the strong relationship between temperature and solubility of wax, wax separation
is a problem in handling and using diesel fuel during cold weather. As fuel cools, a
temperature is reached at which the soluble paraffin wax in the fuel begins to come out of
solution (Cloud Point); any further cooling will cause wax to separate out of solution. The
temperature at which a certain fuel will become saturated with wax and causes filter plugging
problems is termed the Cold Filter Plugging Point (ASTM D6371). The temperature at which
fuel will no longer flow is the Pour Point (ASTM D97). At the pour point, most of the fuel is still
liquid, although it is very thick or viscous and trapped in a honeycomb-like network of wax
Since diesel powered equipment is frequently used at temperatures low enough to cause wax
to separate, a number of techniques have been devised to prevent the wax from causing
problems by plugging fuel screens, lines, filters, and so on, and preventing fuel flow to the
engine. Vehicles designed to operate at very low temperatures have provisions for heated fuel
tanks, insulated fuel lines, heated fuel filters and other mechanisms to warm the fuel so that
the wax does not separate. These more elaborate systems are usually not practical in more
temperate climates where they are needed only a few days a year.
Fuel filters have already been discussed in detail in the Fuel Filters section of this bulletin. The
only additional consideration in terms of common issues with winter fuels is that using a large
filter or multiple filters in parallel will allow more fuel wax to be filtered before a power loss
occurs. Also, relocating the fuel lines and filter out of the wind-stream and wheel splash and
into the engine compartment near the engine block will help keep them warm.
Do not idle the engine for excessively long periods of time with engine coolant temperature
below the minimum specification found in the applicable engine Owner's Manual. This can
result in fuel dilution of the lubricating oil, carbon build up in the cylinder, cylinder head valve
sticking, and/or reduced performance.
There are a number of fuel additives available which reduce the pour point and cold filter
plugging point (CFPP) of diesel fuel. These are commonly referred to as pour point
depressant additives, cold flow improver additives, wax crystal modifiers, or fluidity improver
additives (and can be collectively termed “Winter Additives”). Certain additives can reduce the
Pour Point by as much as 70°F and the CFPP by as much as 30°F. A survey of winter blend
fuels by the Bureau of Mines (now a part of the Energy Research and Development
Administration) revealed that a large percentage of the commercially marketed diesel fuels
had been treated with a winter additive. Before purchasing such an additive to treat fuel, ask the fuel supplier whether the fuel already contains a winter additive. Depending on the amount
and type of additive already in the fuel, additional additives will or will not be necessary.
These additives alter the size and shape of wax crystals, allowing pumping of fuel at lower
temperatures. Although certain additives can be very effective, they are not a cure all. Their
performance varies depending on the paraffin type and content of the fuel treated. Severe
weather applications can require fuel warmers in addition to additives. Although other
additives are available that can provide some benefits, Cummins Filtration™'s Fleet-tech™
Winter Conditioner and Turbo Diesel All Season Fuel Additives are the only fuel additives
recommended by Cummins Inc. to help prevent filter gelling in cold weather applications.
Warming diesel fuel just prior to filtration is an excellent method of preventing fuel filter
plugging. If cold fuel is warmed sufficiently, the wax crystals will dissolve in the fuel. The
dissolving requires warming to a temperature of approximately 11 to 22°C [20 to 40°F] above
the fuel's cold filter plugging point.
In order for a fuel warmer to reliably prevent fuel filter plugging due to wax, it must be capable
of supplying enough heat to the fuel at the maximum fuel flow ( not just fuel consumption) rate
to raise the fuel temperature from the lowest expected fuel temperature (probably the lowest
expected ambient temperature) to 11 to 22°C [20 to 40°F] above the fuel's cold filter plugging
point. There are four different fuel warmers presently offered by Cummins Filtration™ to raise
the temperature of the inlet fuel.
Fuel Filter Heater - The Cummins Filtration™ Positive Temperature Coefficient (PTC) fuel filter
heats the fuel before the fuel flows into the fuel filter. The heater is installed on the fuel filter
head. Most complaints of fuel waxing occur in the fuel filter. The heater uses ceramic discs
that sense the fuel temperature and heats the fuel to a temperature just above the cloud point.
The PTC heater is self-regulating. Depending on battery voltage, the heaters use from 6 to 25
amps at maximum output. When no heat is required, the heater uses less than 0.5 amp. The
heater can be left on during engine operation or it can be turned off with the cab switch. The
heater reaches full heating capacity in about two minutes. The PTC heater kit is available (see
Table 5: Fuel Filter Heaters
Watts Cummins Filtration™ Part Number
A Cummins Filtration™ kit, Part Number 3837317-S, adapts the heater to most fuel filter
heads with 1 in-14 threads. Use to the following fuel filter list to identify fuel filter heads with 1
in-14 threads. The heater adds about one inch in height to the fuel filter head assembly.
Fuel Filter List with 1 in -14 Threads
FF-105D FS-1003 The Cummins Filtration™ kit, Part Number 3832054-S, adapts to FS-1251 filter.
Thermo-Blend™ - The Cummins Filtration™ Thermo Blend fuel warmer recirculates warm
deaerated drain fuel from the engine to the filter and injection system, rather than allowing it to
return to the tank. A 10 to 15 minute engine-running warm up period is usually necessary to
provide successful operation. A built-in thermostat automatically bypasses fuel at 43°C
[109°F]. Part Number 3310200 must be used for all Midrange and Heavy Duty diesel engines.
Part Number 3308750 must be used for all heavy duty off-highway equipment (such as 12 and
16 cylinder engines).
Thermo Blend FM, Part Number 3310630 - The Cummins Filtration™ Thermo Blend FM fuel
warmer combines the return fuel heating principle with a special filter head. When used with
Cummins® Part Number 3315843 (Cummins Filtration™ Part Number FS-1212) fuel-water
separator, it provides fuel dewaxing, water removal, and filtration. A built-in thermostat
automatically bypasses fuel at 21°C [70°F]. When using fuel warmers, do not overheat the
fuel. The maximum fuel temperature at the inlet to the fuel pump is 70°C [158°F]. Alterations
of heating devices must be reversible, or have some means to turn them off during warm
weather operation. The fuel tank is heated by the injector return (drain) fuel from the engine.
On typical installations, the cooling effect of the tank maintains fuel temperatures at an
On some installations, such as acoustically enclosed units, little cooling of the tank occurs
because of the design. On these installations, a fuel oil cooler can be used to limit the
temperature of the fuel at the fuel pump inlet to 70°C [158°F] or less.
Depending on the particular engine model involved, the engine horsepower will begin to
decrease slightly above fuel inlet temperatures of 46°C [115°F]. The percent of power loss is
not as great on Cummins® engines with the PT™ and HPI fuel system (less than 1 percent
per 5°C [9°F]), due to the inherent viscosity compensating characteristics (see Power Loss
section in this bulletin). Operation above 70°C [158°F] is not recommended due to the loss of
the lubricating quality of the fuel with resultant wear to the fuel system components which
depend on fuel for lubrication. A fuel warmer will not help if the fuel is below the pour point and
can not be pumped to the warmer; therefore, in extremely cold conditions, fuel can be treated
with light distillate fuel or treated with a pour point depressant to reduce the pour point, or it
can be necessary to heat the fuel to allow it to flow.
When using fuel warmers that use engine coolant as a source of heat, some form of coolant
heating during shutoff will allow the heater to become effective much more quickly after startup. These fuel warmers must also be checked for leaks. Since the fuel warmer is on the
suction side of the fuel pump and the cooling system is pressurized, any small leak will allow
coolant to enter the fuel system.
Wax in the fuel will deposit in any restriction or sharp bend in the fuel plumbing system. If fuel
starvation occurs during cold-weather operation and plugged fuel filters are not found, look for
plugging of tank pick-up screens, sharp bends in the fuel lines, fittings, and so forth.
Water Contamination Free water (non-dissolved) in the fuel can freeze at low temperatures and the resulting ice
crystals can plug fuel filters, causing fuel starvation. Care must be taken to keep fuel storage
tanks dry. Tanks can be “stuck” often with water detecting paste (usually obtainable from fuel
suppliers) to be sure they are dry. If water is detected, it must be pumped out.
Keeping bulk fuel storage tanks dry has already been mentioned; however, if this is a
persistent issue, a dryer (fuel-water separator) can be installed on the bulk fuel dispensing
Condensation in the vehicle fuel tank(s) occurs when the air in the fuel tank(s) cools down
during a shutdown period. This moisture can be reduced by filling the vehicle fuel tank before
engine shutdown to reduce the air space above the fuel.
Dissolved water comes out of solution as fuel cools. As fuel cools from 4 to -29°C, [39 to -
20°F] the solubility of water in the fuel reduces 70 percent. Therefore, fuel pumped from a
relatively warm underground tank into a vehicle which sits overnight in sub-zero temperatures
can cause some free water to separate. However, this source of free water is almost
negligible, because even at high temperatures fuel will dissolve very little water (0.1 masspercent at 71°C) [160°F]).
Cummins Filtration™ Winter Conditioner Base and Turbocharger Diesel All Season Fuel
Additives are the only additives recommended by Cummins Inc. for this application.
NOTE: More cold weather engine operation recommendations are in Service Bulletin Number
3379009 and in the engine operation and maintenance manual.
Microbial Contamination of Fuel
Although most of the microbes that will live in fuel tanks are common organisms to which
humans are constantly exposed, contact with microbes or fungi from a fuel tank must be
avoided. When a fuel system is contaminated and cleaning is necessary, workers must be
protected. Remember that the fungi produce reproductive spores and when dry these can
easily become airborne, so breathing protection must be provided or the microorganisms must
be kept wet. Dispose of the water and sludge removed from fuel tanks properly. Never place
these materials in sanitary sewer system since they can kill bacteria used in sewage
treatment. Never place them in storm sewers or surface water streams since they can kill fish
and other aquatic animals.
The most common problem associated with exposure to these microbes is dermatitis which in
some people can be quite serious. Any exposed skin must be thoroughly washed with warm,
Avoid eating, drinking and smoking while working with these microbes. Any ingestion of the
microbes or exposure to broken skin must be considered serious. It is recommended that if
this happens the worker be taken to a doctor, along with a sample of the microbes.
WARNING Biocides are generally only mildly toxic to humans and animals but must still be handled
carefully. In cases of ingestion or contact with the eye, follow manufacturer's
recommendations. Seek medical attention.
This section covers the recognition of and solutions to microbial
contamination of diesel fuel.
To protect against fuel shortages, many users have been storing fuel and. As a result, the
frequency of microbial contamination has increased. Microbial contamination of fuel, though
not a new concern, is more common in metalworking industries which use water- soluble oils
as cutting fluids or in long-term storage of hydrocarbon fuels, rather than in diesel fleet
operations. All hydrocarbon fuels are essentially sterilized by the high temperatures
encountered in the refining process; however, they can become contaminated soon after
leaving the refinery by micro-organisms. These micro-organisms, primarily bacteria and fungi,
exist rather harmlessly in moisture-free fuel, passing through fuel systems without having any
However, in the presence of water, these micro-organisms begin to grow and reproduce. The
rate of growth depends on how well the environment suits the particular micro-organism's
The growth of a large colony of micro-organisms in a fuel system can cause several issues.
The first and usually most obvious is fuel filter plugging with a greenish-black or brown slime,
frequently accompanied by a foul odor. This slimy, string-like colony can also plug sharp
bends in fuel lines, fuel meters and other restrictions. The second issue these microorganisms can cause is corrosion due to the acid by-products some of them produce. It is also
possible, if the micro-organisms pass through the fuel filter, that they will form deposits and
cause damage in the fuel pump and injectors.
Some indicators of microbial contamination are:
Slime deposits on tank walls, piping, or other surfaces which are exposed to fuel. These
deposits are usually greenish-black or brown and are slick to the touch.
Black or brown "stringy" material suspended in tank water bottoms.
Swelling or blistering of any rubber surface (washers, hoses, connectors, and so forth) that
comes in contact with fuel.
Sludge or slime deposits on filter surfaces.
Foul odor resembling that of rotten eggs (hydrogen sulfide).
A more conclusive approach is to routinely check the fuel by means of one of the several
available test kits which are listed below. These can detect micro-organisms long before there
is any visible evidence of contamination.
The following list shows test kits of which we are aware. Listing of a kit can not be construed
as a recommendation or approval; and, the fact that a kit is not listed only means we are
unaware of it. Cummins Inc. has not tested any of these kits, but has only reviewed the manufacturer's literature. Users must evaluate the kits available to them and select one based
on their own judgment.
Total Count Sampler, Catalog Number MTOO 000 25 for package of 25, from Millipore
Corporation, Bedford, MA 01730, 1-800-645-5476. The Total Count Sampler contains a
nutrient media specifically designed to encourage bacterial growth; however, many fungi will
grow on it. Millipore recommends incubation at 35°C [95°F] for 24 hours; however, they can be
incubated at room temperature for 36 to 48 hours. If the results on the Total Count Sampler
are low and is still suspected, re-sample using Millipore's Yeast and Mold Sampler (Catalog
Number MYOO 000 25 for package of 25). This sampler contains a nutrient media which
suppresses the growth of most bacteria, but is rich in nutrients for fungi. For best results, use
both samplers each time water bottoms are tested. These Millipore samplers are probably the
most sensitive of those listed, and in fact, can lead one to overtreat a fuel system. Millipore
samplers are also available from Millipore in Australia, Belgium, Brazil, Canada, Denmark,
England, Finland, France, Italy, Japan, Mexico, Norway, Spain, Sweden, Switzerland, and
West Germany. Inquiries from other countries can be directed to Millipore lntertech, Inc., P.O.
Box 255, Bedford, MA 01730 U.S.A.
Microbe Monitor Test Kit (From Air BP) British Petroleum Cleveland-Hopkins International
Airport Cleveland, OH 44135 1-800-533-2340. One sample per kit. Incubates at room
When it has been established that microbial contamination is present and action must be
taken, there are several approaches. The most obvious solution is prevention. Most of the
bacteria and fungi involved are soil organisms which can become airborne or waterborne.
Prevention of the entrance of micro-organisms is not possible because these organisms can
enter the fuel through many different routes.
Growth of these micro-organisms can be prevented. Since all metabolic processes of an
organism are conducted in water, denying the microorganism access to water will prevent
growth, thus preventing the development of large, troublesome colonies. Therefore, the first
and most important step in prevention is to keep fuel systems dry. Keeping a fuel system
entirely dry is impossible. In cases where microbial contamination is a recurring issue, a
microbicide can be used to chemically treat the fuel or the water.
There are three general classes of biocides: water-soluble, fuel-soluble, and universally
soluble. Fuel-soluble biocides are best suited for treating fuels which are to pass through
several storage steps in the distribution process. A fuel-soluble biocide injected into the fuel
early in the distribution system is carried with the fuel through the entire downstream system,
effectively sterilizing the fuel until usage. Fuel-soluble biocides are easier to add to the fuel
system since the exact amount needed to treat a volume of fuel is easily determined and they
have a low toxicity to human and other life forms. The obvious disadvantage to fuel-soluble
biocides is cost; each batch of new fuel added to the system must be treated since the biocide
is consumed as the fuel is consumed.
Water-soluble biocides are more economical for use in treating one step in a fuel distribution
system, such as the end-user's storage tank. The water-soluble biocides, since they are
insoluble in fuel, stay where they are placed until the water bottoms are pumped from the tank;
therefore, the total amount of biocide purchased is less. There are a number of disadvantages
to water soluble biocides. Since no biocide is carried downstream by the fuel, each successive
tank in the system must be individually treated. There is some difficulty in determining how
much biocide to place in a tank since that depends on how much water is in the tank. The
biocide can not be thoroughly mixed with the water in the bottom of a tank. Water-soluble biocides are much more easily taken in by humans and other life forms: and therefore, must
be disposed of properly when water bottoms are pumped from a tank. Water bottoms
containing a water-soluble biocide must not be placed in a sanitary sewer system because the
biocide can destroy the bacteria used by sewage treatment plants. These water bottoms must
be treated as an acidic, industrial oily waste.
Universally soluble biocides are soluble in both water and diesel fuel. They allow you to treat
the entire downstream system. However, each subsequent load of fuel does not need to be
treated. The biocide will remain in any water that has collected at the bottom of the storage
tank and continue to inhibit microbial growth. With certain types of biocides, the interval
between treatments can be as long as six months. Like water-soluble biocides, universally
soluble biocides are more easily taken up by humans and other forms of life. They also tend to
be more expensive than the other types of biocides.
Treating a fuel tank that is infested with a large population of micro-organisms will kill the
micro-organisms, but it will not eliminate the filter plugging they can be causing. The water and
sludge containing the micro-organisms must be removed from the fuel systems. First, clean
the fuel system thoroughly. Next, a fuel-soluble or universally-soluble biocide must be added
to the next few batches of fuel to kill any remaining micro-organisms. Finally, the addition of a
water-soluble or universally-soluble biocide can be continued for at least several months to be
sure the micro-organisms are all dead. If microbial contamination is a recurring issue, it is
recommended that use of the water-soluble or universally-soluble biocide be continued
permanently, since this will be the most cost effective solution to the problem. This can be
done by determining the amount of water that accumulates in tank bottoms between pump
outs and adding about double or triple the amount of water-soluble biocide recommended to
treat that volume of water. For example: you normally pump out approximately 379 liters [100
gallons] of water bottoms. In this case, after pumping the bottoms, immediately add to the fuel
tank two or three times the amount of biocide normally used to treat 37
Fuel Discoloration (Black Fuel)
In some Cummins® engines, normal operation can cause the diesel fuel in the engine and fuel
tank to appear dark or black in color. Discoloration of the fuel can be caused by either: engine
lubricating oil mixing with the fuel during operation, the formation of asphaltenes, or the
degradation of fuel from storage.
Mixing of engine lubricating oil
In some fuel systems, engine lubricating oil and diesel fuel are used in close proximity to each
other for lubricating and sealing purposes. This interface is a function of fuel pump and/or
injector design. Under certain operating conditions, a small amount of lubricating oil can mix
with the diesel fuel and be returned to the tank, causing the fuel to appear dark in color. It
takes a very small amount of lubricating oil (less than 0.1 percent) to cause the fuel to become
visibly darkened. This small amount of oil in the fuel will have no adverse affects on engine
performance, durability, reliability, or emission levels.
This phenomenon is common for fuel systems that operate at very high fuel pressures and
temperatures. The high temperature fuel that is not injected into a combustion cylinder is
returned to the fuel tank. As the fuel is recirculated and exposed to the same high pressures and temperatures during continuous operation, asphaltenes begin to form larger clusters of
insoluble materials that can lead to fuel discoloration. If these formations of asphaltenes grow
large enough, they will be captured by the filter element and can lead to high filter restriction
and shortened filter life.
Asphaltene formation due to fuel overheating can be aggravated by a lack of fuel coolers,
improperly sized fuel tanks, inadequate mixing of return fuel between tanks, low fuel levels, or
installation of the fuel tank that prevents dissipation of heat. If an engine or fuel system cooling
issue is suspected, the cooling systems must be inspected and modified as necessary to
comply with Cummins® requirements. Existing fuel filters could possibly need to be resized or
additional filtration could possibly need to be added to increase contaminant holding capacity.
Consult a local Cummins® Authorized Repair Location for guidance in fuel filter selection and
cooling system issues. Refer to the “Additives” section of this service bulletin for a listing of
Cummins Filtration™ Asphaltene Conditioners.
Degradation of fuel from storage
Refer to the “Microbial Contamination of Diesel Fuel” section of this service bulletin.
Darkening of diesel fuel due to the mixing of lubricating oil or asphaltene formation does not
indicate a manufacturing defect or other warrantable malfunction, and is a function of normal
operation. Customers should continue using the equipment as is, unless the discoloration has
resulted from fuel overheating, fuel contamination, or if fuel filter life is being reduced and
causing operational difficulties with the equipment.
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