Ameer Randolph
It's well known that cars tend to use more fuel in cold weather, but do diesel cars suffer more than other vehicles? The answer is yes—diesel fuel gels in cold weather, and diesel engines are harder to start when temperatures drop below freezing. This is because diesel engines rely on air compression to raise the temperature in the combustion chamber, and in cold temperatures, this takes longer. In addition, refiners have to change the composition of diesel fuel in the winter to help it function better in the cold, and this results in a lower energy value. However, some diesel owners report no noticeable difference in fuel consumption during the winter, and modern diesel engines are improving all the time.
| Characteristics | Values |
|---|---|
| Diesel fuel mileage | Lower in winter compared to summer |
| Diesel fuel in cold weather | Gels up |
| Cold weather effects | Varies by vehicle model |
| Fuel economy loss | 10% to 20% in city driving |
| Fuel economy loss | 15% to 33% on short trips |
| Fuel economy improvement | Park in a warmer place |
| Fuel economy improvement | Combine trips |
| Fuel economy improvement | Minimize idling |
| Fuel economy improvement | Use recommended oil for cold weather |
| Fuel economy improvement | Remove accessories that increase wind resistance |
| Fuel economy improvement | Use a battery warmer, an oil warmer, or a block heater |
| Fuel economy improvement | Add a diesel fuel conditioner with anti-gel |
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What You'll Learn
Diesel fuel gels in cold weather
Diesel fuel contains paraffin wax, which can cause the fuel to gel at temperatures below 32 degrees Fahrenheit (0 degrees Celsius). This occurs when the wax particles within the fuel react to cold temperatures, causing the fuel to become cloudy and eventually solidify. While gelling at 32 degrees Fahrenheit is uncommon, it is quite common for diesel fuel to gel at temperatures of 10 to 15 degrees Fahrenheit (-9 to -12 degrees Celsius) and colder.
The gelling of diesel fuel can cause significant issues for diesel vehicles, including blocked fuel filters and difficulty starting the engine. Therefore, it is essential for diesel vehicle owners, especially those in cold climates, to take steps to prevent diesel fuel from gelling. One effective method is to use diesel fuel additives or anti-gel supplements, which can lower the freezing point of diesel fuel and prevent the paraffin wax from solidifying. These additives can be mixed with the fuel before or after filling up the tank and are compatible with most diesel engines.
Another approach to preventing diesel fuel gelling is to control the temperature at which the diesel engine is stored. Storing the vehicle in a heated garage or climate-controlled structure can help maintain the fuel's flow and prevent it from solidifying. Additionally, mixing diesel fuel with kerosene can lower the temperature at which the wax crystals solidify, though it is important to use kerosene in moderation to avoid potential issues with the fuel pump.
It is worth noting that cold weather can also impact the performance of diesel vehicles beyond the gelling of fuel. Diesel engines generally take longer to warm up in cold weather, and the use of heated seats, window defrosters, and heater fans can further increase fuel consumption. Additionally, driving conditions in cold weather can affect fuel economy, as colder, denser air increases aerodynamic drag, and tire pressure decreases, leading to higher rolling resistance.
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Cold weather reduces fuel economy
Secondly, cold air is denser, increasing aerodynamic drag on a vehicle, particularly at highway speeds. This also affects fuel economy. Thirdly, winter grades of gasoline have slightly less energy per gallon than summer blends. Fourthly, tyre pressure decreases in colder temperatures, increasing rolling resistance. Finally, additional power is used by heated seats, window defrosters, and heater fans. Idling to warm up the car also gets 0 miles per gallon.
The impact of cold weather on fuel economy can be mitigated to some extent. For example, parking in a warmer place, such as a garage, will increase the initial temperature of the engine and cabin. This will also reduce the need to use the heater once the car is in motion. Similarly, combining trips will reduce the amount of driving with a cold engine. It is also recommended to minimise idling to warm up the car and instead drive off gently after 30 seconds. Using the type of oil recommended for cold weather driving by the manufacturer will also help.
Diesel fuel is particularly susceptible to cold weather. Diesel fuel contains paraffin wax components that become less and less soluble as temperatures drop, causing the fuel to gel. This problem can be mitigated by adding a diesel fuel conditioner with anti-gel, which lowers the freezing point of diesel fuel. However, refiners also change the composition of diesel fuel in the winter to improve performance in cold weather, and these blends tend to have slightly lower energy value.
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Winter diesel fuel has a lower energy value
It is a well-known fact that gas mileage decreases in winter. This is partly due to changes in the composition of winter gas, which is made more volatile to burn properly in cold weather. Diesel vehicles are also affected by this phenomenon, and users often complain about lower mileage during the winter months. This can be attributed to changes in the diesel fuel composition, specifically the need to reduce sulfur levels and improve cold gelling performance.
The process of removing sulfur from diesel results in ultra-low sulfur diesel (ULSD), which has approximately 3% less energy value than its predecessor, winter low-sulfur diesel. This reduction in energy value leads to a decrease in the number of miles travelled per gallon. To counteract this issue, refiners may mix in additional product "streams" to modify the properties of winter diesel, thereby lowering its gelling temperature. However, these modifications also contribute to a reduction in the overall energy value of the fuel.
For instance, consider the comparison between normal #2 diesel fuel, which has approximately 140,000 BTUs of energy per gallon, and kerosene, which has approximately 130,000 BTUs. By blending in more kerosene, the total energy value decreases. Additionally, aromatic chemicals and naphtha, which can be added to diesel fuel by refiners, may provide a wider temperature margin before the fuel gels in cold weather. However, these additives also result in a lower energy value and, consequently, lower mileage.
The impact of cold weather on fuel economy is not limited to the fuel itself but also extends to the vehicle's performance. Colder air is denser, increasing aerodynamic drag, particularly at highway speeds. This increased drag demands more fuel to maintain the same level of balance. Furthermore, engine and transmission friction increase in cold temperatures due to the lower viscosity of engine oil and other drive-line fluids. This heightened friction prolongs the time it takes for the engine to reach its most fuel-efficient temperature, affecting shorter trips more significantly.
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Cold air is denser, increasing drag
It is a known fact that cold weather can reduce fuel economy in vehicles. This is true for both gasoline-powered and diesel-powered vehicles. While modern diesel engine technology has made it easier to start vehicles in cold weather, diesel engines still face challenges in extreme cold.
One of the main reasons for the decrease in fuel economy in cold weather is the increase in aerodynamic drag on the vehicle. Colder air is denser, which means there is more air in each cylinder. As a result, more fuel is required to reach the same balance point. This increase in density leads to higher resistance when driving, especially at highway speeds. The denser air acts as an obstacle, making it harder for the vehicle to move through the air, similar to how a person would experience more resistance when trying to walk against a strong wind.
The impact of cold air density on fuel economy is more significant in short trips or city driving. This is because the engine spends a larger proportion of the trip at less-than-optimal temperatures. The engine takes longer to reach its most fuel-efficient temperature, and the constant stops and starts in city driving prevent the engine from maintaining this temperature. As a result, the vehicle uses more fuel to maintain speed and acceleration.
Additionally, cold temperatures affect the performance of various components in the vehicle. For example, tire pressure decreases in colder weather, increasing rolling resistance. This means that the tires require more energy to turn, further reducing fuel economy. Cold temperatures also impact the engine oil and other drive-line fluids, increasing friction and reducing efficiency.
To mitigate the effects of cold weather on diesel vehicles, there are several measures that can be taken. Parking in a warmer place, such as a garage, helps increase the initial temperature of the engine and cabin. Combining trips and minimizing idling can also help reduce the amount of driving with a cold engine. Using the type of oil recommended for cold weather driving and removing accessories that increase wind resistance can also improve fuel economy.
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Engines take longer to warm up in cold weather
Diesel engines rely on air compression to raise the temperature in the combustion chamber high enough for the fuel to ignite spontaneously. In cold weather, this process becomes more difficult as the air is denser and colder, requiring more fuel to achieve combustion. This increased density also affects the vehicle's aerodynamics, increasing drag and reducing fuel efficiency.
Additionally, diesel fuel itself is more susceptible to gelling in cold weather due to its paraffin wax components becoming less soluble. This can clog fuel filters and affect engine performance, leading to increased fuel consumption. To counteract this, refiners adjust the composition of diesel fuel in winter, making it more volatile to improve cold-weather performance. However, this also results in a slight reduction in energy value, contributing to lower mileage.
The impact of cold weather on engine warm-up times is more pronounced for shorter trips, as the engine spends a larger proportion of the journey at sub-optimal temperatures. This, combined with the use of heated seats, window defrosters, and heater fans, which all draw additional power, can significantly affect fuel economy.
To mitigate these issues, diesel vehicle owners can take several measures. Parking in a warmer place, such as a garage, helps increase the initial engine temperature. Combining trips and minimizing idling can also reduce the amount of driving done with a cold engine. Using the correct type of oil for cold weather driving and ensuring proper tire pressure can further improve fuel efficiency. For extreme cold, additional measures such as battery warmers, oil warmers, or block heaters may be necessary to keep the engine warm.
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Frequently asked questions
Yes, diesel cars can use more fuel in cold weather. This is due to a combination of factors, including the gelling of diesel in cold weather, the use of heaters and heated accessories, and the increased drag caused by denser, colder air.
In cold weather, diesel fuel can gel or thicken due to the reduced solubility of its paraffin wax components. This can make it harder for the fuel to flow through the engine and affect its performance. To counter this, refiners adjust the composition of diesel fuel in winter, making it more volatile to improve cold-weather performance. However, this also results in a slightly lower energy value, leading to reduced mileage.
Here are some tips to improve the fuel economy of your diesel vehicle in cold weather:
- Park your car in a warmer place, such as a garage, to increase the initial temperature of the engine and cabin.
- Combine trips to reduce the amount of driving with a cold engine.
- Minimize idling and drive off gently after about 30 seconds to allow the engine to warm up faster.
- Avoid excessive use of seat warmers, window defrosters, and heater fans, as these use additional power.
- Maintain proper tire pressure and use tires appropriate for the season.
- Use the type of oil recommended by the manufacturer for cold-weather driving.
- Remove accessories that increase wind resistance, such as roof racks, when not in use.
