by Jeff Walkup
Owners of diesel operated equipment in Canada and northern USA can attest to the fact that as temperatures drop, the overall performance of their diesel engines also drops. Diesel fuel does not fare well in cold temperatures – it can start to form crystals that clog fuel filters and fuel lines. Prolonged freezing temperatures can cause engines to not operate properly or not start at all.
Cold Weather Diesel Fuel Issues
Diesel engines can experience cold starting issues because of water and/or fuel gelling which can significantly impact on diesel fuel filters.
Water
Water is almost always present in diesel fuel to some degree. A substantial quantity can accumulate in storage tanks or vehicle tanks if it isn’t removed periodically. Since water is heavier than fuel, it settles to the bottom of the fuel tank. You’d be okay if it stayed there, even frozen, but it never does. Warm fuel melts the water which then sloshes around in the tank when the equipment is moving.
The water breaks up into finer droplets that can then freeze as it travels through fuel lines exposed to cold outside air. You can especially experience this problem at the metal 90-degree-bend fittings in fuel lines. The metal is cold, the 90-degree bend slows the flow and water that is trapped there can freeze, eventually plugging the line. Ice crystals that make it past a 90-degree bend will next hit the fuel filter filtration media. In the past, when filter media was measured in 10s of microns, tiny ice crystals easily passed through the media. With today’s 2-micron filters, ice will be trapped by the filter. If enough ice accumulates on the filter media, fuel will no longer flow through the filter and the engine will quit.
Fuel Gelling
Gelling occurs when the paraffin wax in diesel fuel solidifies because of a drop in temperature. When cold soaked, the paraffin wax present in diesel solidifies, giving the fuel a cloudy appearance. The fuel can begin to cloud at temperatures as high as 32°F (O°C), but it will continue flowing. The fuel must stay very cold (below -10°F (-23°C)) for long periods (48-72 hours) before it will actually gel. The reason diesel fuel has a wax component is because it gives fuel a good cetane value. Cetane offers power and better engine responsiveness. Wax content is lower in the winter fuel, but remains in diesel blends for cetane.
Fuel Filters
While “gelling up” may be a common phrase, it’s probably not the real reason your engine no longer runs. It’s not uncommon to hear operators complain about their fuel gelling up, but the more likely problem is ice or solidified paraffin wax in the fuel filter. Frozen water can clog fuel lines and fuel filters, which starves the engine of fuel. Water freezes at a much higher temperature than does fuel, so if you’re experiencing problems at temps ranging from 20° to 30°F, you probably have ice in your fuel lines or fuel filters. Pop the filter off and look inside; ice looks like, well, ice, and frozen wax is thick and gooey.
Prevention Considerations
Changing your fuel filter to one with more porous media is not the answer to cold temperature fuel issues. Today’s high-pressure fuel injection systems have very tight internal clearances, and any debris can cause significant and costly damage. Were you to use a more porous filter, the ice that would clog a smaller filter would melt under the heat and pressure in the injection system long before it got to the sensitive fuel injectors. However, other particles present in the fuel would pass through too, possibly damaging the pump or injectors. Remember, you get water in the fuel from many sources – from condensation (warm fuel/cold temperatures), sludge in the bottom of the storage tanks, and poor-quality fuel delivery from your vendor. It’s everywhere, and it’s probably in your tanks too.
Proactive planning for cold weather is key to ensuring your diesel fuel, and engines, are not severely impacted by severe temperature drops. When developing your winterization plan, consider the following:
- Anti-gel Additives: You can use a commercially available, anti-gel fuel supplement. Anti-gel additives are easy to use – you just top off your fuel tank with the treatment. Anti-gel additives drop the freezing point of diesel fuel so that it is less likely to freeze in cold temperatures. Anti-gel additives are designed to lower the Cold Filter Plugging Point (CFPP). The CFPP is the lowest temperature at which fuel will still flow through a specific filter and operate in the combustion process.
- Winter Diesel: Winter blends supplied by fuel manufacturers are a mix of #2 and #1 diesel. Fuel normally used in the warmer months is #2 diesel and contains the liquid form of paraffin wax. The #1 diesel fuel is more refined and less likely to gel in cold weather. Winter blends can be blended to meet the needs of companies operating in different regions and weather conditions.
- Kerosene: Blending kerosene into #2 diesel fuel lowers the cloud point of the fuel (or the temperature at which the paraffin wax begins to crystalize). The rule of thumb is that for every 10% kerosene blended the CFPP is lowered by 3°F. Kerosene blending often starts in the fall and continues through the winter months into the spring. Note that it’s more cost effective to treat fuel with a winter fuel additive than to cut fuel with kerosene. Additionally, kerosene can reduce fuel efficiency and engine performance and because it can reduce the lubricity of diesel fuel and cause premature failure in engine components.
- Diesel Fuel Testing: Fuels should be tested prior to winter to determine expected performance in cold weather, It’s also important to test bulk storage tanks for water and other contaminants.
Before making any modifications to your fuel, you should work in close collaboration with your fuel vendors and get the best quality fuel for your winter applications. In addition, follow maintenance best practices in winter and do routine diesel fuel testing so you can maintain a consistent level of performance.