Preventing Cold Weather Diesel Problems
Cold Weather Diesel Operations
Depending on the severity of winter conditions, operators may choose to cold protect their equipment by multiple means. First it is assumed that the fuel purchased is blended for cold weather use. However that’s no guarantee that the weather will cooperate. To prepare for expected and unexpected cold weather operating conditions, fuel additives, fuel heaters, and heated fuel water separators can offer protection.
A Word of Caution: Never add gasoline or alcohol to diesel fuel to help with cold weather operation. The practice creates an explosion danger and will damage the fuel injection system.
Heating diesel to above its cloud point is the best way to avoid winter engine power loss. There are three common sources of heat energy that are available for fuel heating: electricity, engine coolant, and the heated fuel re-circulating from the engine back to the fuel tank.
Electric Heaters come in two types, PTC and Resistance. Because of on-vehicle power limitations, electric heating cannot sufficiently heat high fuel flows. However, if paraffin wax begins to plug the fuel filter, the flow through the filter begins to slow until the flow rate is low enough for the fuel heater to be effective; and the filter can still pass sufficient fuel to allow the engine to run and get warmed up. This flow may not be sufficient to run the engine under load.
PTC heaters use disc-shaped “PTC” (positive temperature coefficient) heating elements that are attached to a heat sink plate which transfers the generated heat to the flowing diesel fuel. These heating elements are temperature self-regulating. They are most effective when fuel is constantly moving over them to take the heat away. When flow stops and/or the temperature rises, PTC heaters will self-regulate down to 1 to 2 amps current draw. Because of this, pre-heating with a PTC heater is less effective than with a resistance heater.
Resistance heaters are like the heating elements used in electric stove tops. These produce constant heat whether the fuel is flowing or not. Because of this, they have superior performance when pre-heating the fuel system at startup. Mounted inside filters, they need a thermostat and failsafe fuse protection to be used safely. Blanket or wrap-around supplemental heaters are available that can be fastened to the outside of filter housings for severe weather conditions. These, however, are only energized when the vehicle is parked. They operate on 110 VAC along with engine block and tank heaters and allow easy start up on cold mornings. For extreme environments, self-regulating heated fuel lines are also available.
Because of electrical power limitations on vehicles, electric heaters are best located as close to filters and screens as possible. Usually that means the heater location is where warmed fuel flow or convection can carry heat to the filter media where wax crystals clog filters. Electric heaters can be installed on top of the fuel filter where cold fuel flows into the filter housing or at the bottom of the filter where convection can help carry heat to the media.
Engine Coolant is another source of heat energy that, through the use of a heat exchanger, can transfer excess cooling system heat to the fuel. In conjunction with electric heat at engine startup, a coolant/fuel heat exchanger can supply an enormous amount of heat to the fuel at high flow, effectively eliminating any chance of cold fuel filter plugging.
Return Fuel Heaters are the most efficient way to add heat. They work by allowing the engine heated “return fuel” to enter back to the inlet side of the filter instead of directly back to the fuel tank. The warm return fuel makes up a major portion of the inlet fuel, reducing the amount of cold fuel supplied from the tank. A thermally controlled valve diverts all the return fuel to the fuel tank when the fuel in the tank is warm. In conjunction with electric heating of the returning fuel, this method can be highly successful.
Cold Flow Improvers
The only way to actually lower the cloud point temperature is to dilute #2 diesel with #1 diesel or kerosene. However, this lowers the fuel heat value and adds cost. Alternately, widely available cold flow improvement additives may help delay filter plugging. They lower the pour point of diesel fuel several degrees, but do not change the cloud point temperature. Instead, cold flow improvers work by altering the paraffin crystal shapes to needle-like forms. More of the needle-shaped crystals can pass through the filter element, slowing the plugging process.
Getting Things Running Again
Using heat to prevent wax formation in diesel fuel is much preferred to troubleshooting a fuel system already shut down by the cold. Before the cold weather sets in you should be prepared by following the wax prevention steps detailed above. Failing that, once waxing has occurred it can only be eliminated by either physically removing the blockage, or warming the fuel to re-dissolve the wax crystals. Be aware that melting the wax may require a longer heating time than expected. No suitable solvents or additives are available that will dissolve wax once it has crystalized out of the fuel.
A cartridge filter can be removed from its housing and gently warmed until the crystals are gone. If it becomes obvious that most of the crystals are ice, or if the wax resists melting, it is best to simply replace the filter. If dealing with spin-on filters, gentle warming as described below may unblock the filter. Replacing the filters may provide a better result.
Fine mesh screens fitted in the fuel tank are also a common source of difficulty. To get things running again apply gentle heat to the fuel system (filter body and fuel lines). Hot water, steam cleaners, fan heaters or even a hair dryer can be used. Then start the engine and run until the system is warm. Under no circumstances should a naked flame be used on any part of the fuel system or fuel tank.