CFPP stands for cold filter plugging point, the lowest temperature at which diesel fuel can still pass through a standard filter without clogging. It’s the single most important number for predicting whether a diesel engine will run reliably in cold weather. When fuel drops below its CFPP, wax crystals form and block the fuel filter, starving the engine of fuel.
How CFPP Is Measured
The standard test is straightforward. A 20-milliliter sample of fuel is cooled gradually while being drawn through a fine mesh filter (45 microns, roughly half the width of a human hair) under light vacuum pressure. The fuel must pass through the filter in under 60 seconds to count. The temperature keeps dropping in small increments, and each time, the test is repeated. The CFPP is the last temperature at which the fuel successfully passes through. One degree colder, and the wax crystals in the fuel have grown large enough to block the mesh.
Two internationally recognized standards govern this test: EN 116 in Europe and ASTM D6371 in North America. Both manual and automated versions of the apparatus are accepted for official results.
CFPP vs. Cloud Point vs. Pour Point
CFPP is one of three cold-weather measurements you’ll see on a diesel fuel spec sheet, and each one captures a different stage of the same process: wax forming as fuel gets cold.
- Cloud point is the temperature where wax crystals first become visible, giving the fuel a cloudy appearance. This is the earliest warning sign. It’s always higher (warmer) than the CFPP because crystals are just beginning to form and haven’t yet grown large enough to block anything.
- CFPP is the practical danger zone. The crystals have grown enough to clog a fuel filter. Your engine will struggle or stop running at this temperature.
- Pour point is the temperature where the fuel becomes so saturated with wax that it won’t flow at all, even without a filter in the way. It’s the coldest of the three measurements.
Of these three, CFPP is considered the most useful for real-world performance because fuel filters are the first bottleneck. Your engine will lose power long before the fuel itself refuses to pour.
What Happens When Fuel Hits Its CFPP
When diesel fuel cools to its CFPP, the wax crystals that have been forming since the cloud point grow large enough to coat and block the fuel filter. The consequences cascade quickly. The fuel pump can’t push enough fuel through the clogged filter, so pressure drops at the injectors. You’ll notice hesitation during acceleration, reduced power when climbing hills, and engine misfiring as individual cylinders receive too little fuel to combust properly.
If temperatures keep falling or the filter becomes fully blocked, the engine will stall. Many diesel vehicles have a dashboard warning light that illuminates when fuel pressure drops below a critical threshold. Left unaddressed, a wax-clogged filter also forces the fuel pump to work harder than it’s designed to, which can damage the pump over time.
CFPP Requirements by Climate
Europe’s EN 590 diesel standard sets specific CFPP limits depending on the climate where the fuel will be sold. For temperate regions, there are six grades:
- Class A: +5 °C (mildest, summer fuel)
- Class B: 0 °C
- Class C: −5 °C
- Class D: −10 °C
- Class E: −15 °C
- Class F: −20 °C (harshest temperate winter fuel)
For arctic regions, the requirements go much further, with five additional classes ranging from −20 °C down to −44 °C. Fuel sold in Scandinavia or northern Canada in winter must meet these extreme ratings. Gas stations in cold climates typically switch to a lower-CFPP diesel blend as winter approaches, often called “winter diesel” or “arctic diesel.”
Biodiesel and CFPP Challenges
Biodiesel generally has worse cold-flow performance than petroleum diesel. The exact CFPP depends heavily on the feedstock. Biodiesel made from animal fats or palm oil tends to have a higher CFPP (meaning it clogs filters at warmer temperatures) because these fats contain more saturated fatty acid chains that crystallize easily. Biodiesel from waste cooking oil, for example, has been measured with a CFPP around −5 °C before treatment, which is significantly warmer than what’s needed for cold-climate winter driving.
This is one reason biodiesel is commonly blended with petroleum diesel rather than used pure. A B20 blend (20% biodiesel, 80% petroleum diesel) has a much lower CFPP than B100, making it more practical for year-round use.
How Cold Flow Improver Additives Work
Chemical additives can lower a fuel’s CFPP by several degrees. The most common type uses polymer molecules that attach to the surface of wax crystals as they form. By coating the crystals early, these additives prevent them from clumping together into large masses. Instead of growing into flat, plate-like structures that easily block a filter mesh, the crystals stay small and needle-like, passing through the filter rather than piling up on it.
Research on biodiesel has shown this effect clearly under microscopy. Without additives, large crystalline clumps form rapidly as fuel cools from −10 °C to −20 °C. With a flow improver present, only small, scattered needle-shaped crystals appear at those same temperatures. In one study on waste cooking oil biodiesel, treatment with additives lowered the CFPP from −5 °C to −12 °C.
These additives are widely available as aftermarket products for diesel vehicle owners, and fuel refiners also blend them into winter diesel formulations before the fuel reaches the pump. They’re effective, but they have limits. No additive can make a summer-grade diesel safe for deep-winter use in an arctic climate. Choosing the right seasonal fuel grade is still the first line of defense.