#1 vs. #2 Diesel Fuel
Diesel fuel is available in two grades, #1 and #2, as well as a “winterized” blend. There are major advantages and disadvantages for each grade of fuel, though you can run both in your engine without any complications.
#2 Diesel Fuel is what’s available most of the time at your local fuel station. #2 diesel has the highest energy content and lubricity. The high energy content translates into the best possible performance and fuel economy, while the lubricity of #2 diesel protects injection pumps and other engine components. It is also less expensive than #1 diesel, as it does not require as much refinement to produce. The downside of #2 diesel is that it gels (thickens) at a higher temperature than #1 diesel. Fuel gelling leads to hard starts and related complications in cold weather.
#1 Diesel Fuel has a lower energy content (about 5%) than #2 diesel and is slightly more expensive. However, it does not gel like #2 diesel because the paraffin (wax) has been removed from the fuel. While this keeps the fuel flowing in cold weather, paraffin is an important lubricating compound found in #2 diesel. Regardless, some diesel engines are designed to operate solely on #1 diesel.
Winterized Diesel Fuel is a blend of #1 and #2 diesel fuels, typically on the order of 15-20% #1 diesel by volume. Winterized fuel blends are released when the weather becomes too cold for #2. By combining both types of diesel, the fuel contains adequate energy content and acceptable lubrication properties while reducing the risk of fuel gelling due to cold temperatures. Fuel economy typically drops slightly during the winter due to the decreased energy content of winterized fuel.
Using #1 diesel will not cause any immediate concerns, though sustained usage in an engine designed to run on #2 diesel may reduce the life of your fuel system (and injection pumps don’t come cheap!). Obviously, #1 and #2 diesel fuels can be mixed, and you shouldn’t be afraid to fill up with #1 if that is all that is available to you at the time.