Right Fuel Blend Can Stop Gelling
Published: Friday, January 30, 2026
If you've ever found yourself standing next to a diesel engine that refuses to start on a cold winter morning, you know the sinking feeling that comes with it. Whether you've got a farmyard full of snow to clear or a generator keeping your business going, a frozen-up diesel engine can really put a stop to your plans in a hurry.
There are several reasons diesel fuel has issues in the winter. Before your diesel fuel gets to the engine, it's filtered to remove impurities. That filter can become a trouble spot when temperatures dip.
In No. 2 diesel fuel, there's a naturally occurring substance called paraffin wax. Under normal conditions, this wax stays in liquid form and doesn't cause any issues. But when the temperatures drop, that wax begins to solidify, forming crystals that cannot make it through the filter. This is the condition folks call "gelling."
Gelling starts at what is called the cloud point. That's the temperature at which paraffin wax starts to crystalize. You might notice a white haze or "cloud" in the fuel. For most No. 2 diesel, the cloud point is around 14 degrees F. If the temperature continues to drop, those wax crystals can build up and clog the fuel filter, starving the engine of fuel. That's when you hit what's known as the cold filter plugging point (CFPP), the temperature at which the fuel can no longer flow through a filter. For most No. 2 diesel, CFPP is just a few degrees below the cloud point.
Here's the kicker: Newer diesel engines require filters that are even finer than the ones used in CFPP tests. That means modern tractors and generators could start having trouble with gelling and plugging at higher temperatures than the CFPP ratings. So, while CFPP is a handy guideline, it's not foolproof, especially for today's high-tech filters.
Both the cloud point and CFPP are natural properties of the fuel itself, which means you can't change them. But there are steps you can take to keep your engine running, even when the temperatures drop.
You can't stop the wax from crystallizing, but there's a trick to make it easier for the wax to flow through the filter: change the shape of the crystals. This is where a cold flow improver (CFI) comes in. A CFIworks by breaking up those wax crystals into smaller, more manageable pieces, making it possible for them to flow through the filter without causing a blockage. These additives can typically keep your diesel flowing smoothly down to about 0 degrees F.
Adding a CFIis a great first step toward keeping your diesel running in the cold. But as the weather gets colder, you'll want to switch your No. 2 diesel to No. 1 diesel, which doesn't have the wax and is far better suited for freezing temperatures. Most fuel providers in our region begin blending No. 1 and No. 2 in November, but if you have some old diesel in the tank or in storage, it might be unsuited for our recent cold temps.
When the temperature dips below 35 degrees F on average, start blending about 70% No. 2 diesel with 30% No. 1 diesel, and add in that CFI. Our average low monthly temperature hits 32 degrees in November and doesn't exceed 35 degrees again until April.
Our coldest monthly average temperature in this region is 17 degrees in January. In the depths of winter, you'll want a blend of about 30% No. 2 and 70% No. 1, and still add in that CFI. For top-notch low-temp operability, look for winterized diesel blends designed specifically for cold weather.
While it's rare for us, once it gets below -30 degrees F, it's time to go straight No. 1 diesel. For maximum protection, use No. 1 diesel along with an appropriate fuel additive to keep things running smoothly.
While you're winterizing, don't forget to watch out for fuel icing. Icing can look a lot like gelling, but instead of wax crystals, it's actual water ice crystals. It's a bigger issue because it means water has gotten into your fuel system. Frozen water can expand and bust all sorts of things in your engine. The most common way water enters a fuel tank, besides poor quality fuel, is from condensation that occurs when a storage tank is near empty and the air in the tank gets cold. Keeping the tanks full can reduce the chances of icing.
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