Why diesel gels in the cold, but gas doesn’t – Jalopnik

Diesel engines are known for their reliability, longevity and torque – until winter arrives and reminds them that chemistry still applies. Diesel fuel, which is pricey these days, behaves differently in the cold. When the temperature drops far enough, it can change from a free-flowing liquid to something more like a milkshake.

The paraffin wax in diesel fuel is the cause of this change. As temperatures drop, wax crystals begin to form in a process known as turbidity. At somewhere between 10 and 15 degrees Fahrenheit, depending on the fuel mixture, those crystals become large enough to clog the fuel filters and restrict flow. This is why diesel takes the form of a gel, starving your engine. Fuel injectors cannot get a steady supply of diesel, pumps become overloaded and combustion becomes inconsistent or stops altogether. That’s why symptoms often include hard starting, rough idling, loss of power, or complete stalling. Gelling can happen even while driving as the fuel tank is located a bit far from the engine heater.

Gasoline does not suffer this fate because it does not contain paraffin wax. Instead, lighter hydrocarbons are used, which remain liquid at much lower temperatures. Although gasoline can freeze under extreme conditions (about -40 degrees Fahrenheit to -200 degrees Fahrenheit), it does not crystallize in a way that blocks fuel systems. Diesel fuel is less forgiving when cold weather arrives uninvited, and using it can lead to one of the worst winter driving experiences of your life.

If your diesel has already gelled, the solution is simple, but not immediate. Check the fuel tank and fuel filter to confirm the presence of cloudy oil. If you see that, there is a good chance that the filter is clogged. The fuel system requires heat, so it is wise to move the vehicle to a heated area such as your garage. You can also apply external heat, such as from an engine block heater, to warm the engine and fuel system. As soon as the temperature rises, the wax crystals should dissolve again in liquid fuel. Depending on how cold it got and how gelled the system is, this process could take several hours. You’ll want the help of a de-gel treatment designed to reliquefy wax and remove filters. Also watch out for icing on diesel fuel, which mimics gelling symptoms and causes its own problems in cold weather.

Either way, it’s better to avoid gelled fuel completely. Use winter diesel – preferably a 70/30 blend (70% diesel #2 and 30% diesel #1) – when temperatures drop. Add anti-gel additives, such as a cold flow improver, as these will keep the fuel flowing smoothly through the filter even when it is cold enough to gel. And keep your tank relatively full to reduce condensation. You can also use kerosene to thin the diesel engine and the wax.

Diesel does not fail in winter. It just shows some problematic behavior in the cold. Plan ahead or those low temperatures will ruin your diesel engine.