If it seems it’s easier to “gel” modern diesel engines, it’s true. The design of Tier III and newer diesel engines, combined with the use of Ultra Low Sulfur Diesel (ULSD,) increase the chances of gelling fuel in cold weather.
Diesel fuels thicken when wax, a normal, necessary lubricative component of #2 diesel fuel, crystallizes at low temperatures. The “cloud point” for #2 diesel is around 32° F. The “gel point” for summer-grade #2 diesel varies between 10 to 20° F.
Modern diesel engines gel more easily because their EPA Tier III and newer injection systems require fuel filtered to as little as two microns. Wax crystals in chilled diesel fuel measure 50- to 250-microns. With 2-micron filters, even “cloudy” diesel fuel can restrict flow.
To compound the filter-clogging conundrum, USLD fuel mandated to meet EPA standards is more “hygroscopic” that Grandpa’s diesel fuel. That means it attracts water. Water-separating filters on modern diesel engines catch most of the water, but microscopic droplets may remain suspended in the fuel. When the fuel temp falls below 32°F, the water droplets freeze. If they’re larger than 2 microns, they contribute to clogged fuel filters.
So yes, modern diesel engines gel more easily than older engines. That’s cold comfort if you forgot to change to winter-grade fuel or add anti-gel additive before the weather turned frigid, but it’s the truth.
