Cold weather can be especially punishing for diesel engines. With winter approaching, truck drivers are preparing for the typical winter diesel problems. One of the most common diesel engine problems that occur in cold weather is the engine taking longer to crank up or not starting up at all. A frequent cause of diesel engines not starting in cold weather is a wax build-up in the fuel filter. In this article, we will take a quick look at what wax build-up is, its causes, and what you can do to minimize wax build-up in diesel engines.

Causes of Winter Diesel Problems

A small percentage of all diesel fuel contains a paraffin wax which helps diesel engines produce more energy from the fuel. This diesel wax also improves fuel viscosity and lubrication. This wax, at mild to hot temperatures, exists as a liquid. However, in cold weather, the wax crystallizes, and if the temperature outside drops too low, then enough of these crystals can build up and block your engine’s fuel filters and fuel line. This “gelling” leads to diesel engine fuel starvation, which can lead to the engine’s not starting or becoming hard to start. 

There are three stages of wax build-up in diesel engines, each of which occurring as the temperature lowers. These are the cloud point, pour point, and cold filter plugging point. 

Cloud point: The cloud point is the point at which paraffin wax in your diesel fuel begins to form crystals. At this point, the wax in your fuel will begin coating your diesel’s fuel filters. Because of the variability in diesel fuel, every station could be different. For this reason, it’s hard to find an exact cloud point, but wax crystal formation in your fuel could start as warm as 40 degrees Fahrenheit. 

Pour point: Your diesel engine experiences the pour point next, and this is the point that the wax and wax crystals in your diesel fuel form a gel-like consistency. The pour point generally begins around the 32-degree Fahrenheit mark. This gel can clog your diesel engine’s fuel filters and begin to cause problems. 

Cold Filter Plugging Point: Diesel fuel that is in a gel-like state can still flow through the engine until it reaches the cold filter plugging point. The cold filter plugging point is the lowest temperature that a volume of diesel fuel can pass through a filtration device. 

Identifying Wax Build-up in Diesel Engines

If your diesel engine has a hard time starting or won’t start at all in cold weather, the wax build-up could be the culprit. If wax crystals have formed in your diesel fuel, blocking fuel lines and filters, it can be visible as white or yellow cloudiness in your fuel. Diesel fuel waxing sometimes causes low oil pressure as well. 

How to Prevent Wax Build-up in Diesel Engines

Preventing wax build-up in diesel engines, like many diesel-related engine problems, depends on performing regular fleet maintenance by expert diesel engine technicians. Preventative maintenance is the most critical aspect of driving a truck and can ensure that your vehicle runs efficiently no matter what the weather. 

Climate Control Truck Parking

While you generally don’t have to worry about wax build-up in your engine while it is running, when your truck is parked, it’s a different story. While it is not always available, storing your truck in a heated garage or climate-controlled building will certainly help prevent wax build-up. 


Mixing a specific amount of kerosene in with diesel fuels will reduce the plug point temperature and keep wax crystals from forming. Winter climate fuel suppliers sometimes offer diesel fuel pre-mixed with kerosene. 

Fuel Additives

Another step in preventing wax build-up in your diesel engine during the winter months is to add a diesel flow improver additive to your fuel. Diesel flow improver lowers the cold flow point of diesel fuel and prevents wax crystallization. These additives also change the shape and structure of the crystals that do form, preventing them from combining and overwhelming your fuel filter. When using them for preventative measures, diesel flow improver additives should be added at 10 degrees above the cloud point temperature.

Fuel Eaters

If you have already confirmed that you have fuel starvation caused by diesel fuel wax build-up, you’ll need to call in the “big guns”. Unique fuel eaters are available if your fuel has already reached the gel-like, cold filter plugging point. 

Overnight Heater

Numerous manufacturers supply plug-in, overnight cold weather heaters that warm your fuel during the evening when you are parked. Most models will use the same power outlet used for engine block heaters. 

Coolant Heaters

Coolant heaters work under the same principle as the overnight heaters but utilize heat from your coolant to warm fuel. The heat from the refrigerant is routed through the coolant manifold to heat the coolant heater, and this heat is then transferred in the engine’s fuel.  

Use Winter Fuel

Diesel fuel specifications vary widely across the country, as well as by the month of when it is produced. Therefore, diesel fuel produced during the summer will have a higher cloud point and shouldn’t be used during winter. Plan on changing over fuel by May of each year at the latest. Special “alpine diesel” is available for drivers traveling in alpine regions during winter. 

Cold Weather Lubricant

Of course, you always want to use the correct type of lubricating oil for your diesel engine to give it the maximum protection and starting power. When a diesel engine is diluted by fuel, the wax build-up can occur in the oil, causing it to solidify as well. 

Fuel Tank, Filter, and Line Insulation

One of the most cost-effective preventative measures to combat wax build-up is to insulate your fuel tank, fuel filters, and fuel lines. Left exposed, your diesel’s fuel elements cool much more quickly. 

Winterize Your Diesel Engine 

Once wax build-up in your diesel engine reaches a certain point, you may have to have fuel filters changed as older filters have a more difficult time dealing with even small amounts of wax. It might be necessary to raise the temperature of the fuel with a blow heater in emergencies. With winter weather on the way, now is the time to get your truck prepared for colder temperatures. Call Certified Diesel Solutions today to have your rig winterized or to inquire about complete fleet management services. We can be reached online or by phone at (865) 964-6598.