How Cold is Too Cold for a Diesel Engine? How To Keep Your Engine Running Smoothly

Patrick Oziegbe
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If you own a diesel engine, you know that cold weather can significantly impact its performance.

While diesel engines are known for their durability and efficiency, they require extra care and attention in cold weather to ensure they start and run smoothly.

So, how cold is too cold for a diesel engine?

Diesel engines are harder to start in cold weather because they depend on high temperatures created by compression to ignite the injected fuel.

It is five times harder to start a diesel engine at 0°F (-18°C) than it is at 80°F (27°C).

Cold weather can also cause the diesel fuel to gel or solidify, potentially disrupting normal fuel flow and causing difficulties in starting the engine or hindering its performance.

It would help if you took extra precautions to keep your diesel engine running smoothly in cold weather.

I’ll show you the impact of cold weather on diesel engines, the role of glow plugs and block heaters, battery performance, fuel additives and their benefits, and more.

By the end of this article, you will better understand how to maintain your diesel engine in cold weather.

How Cold is Too Cold for a Diesel Engine

Key Takeaways

  • Diesel engines are harder to start in cold weather and can experience fuel flow disruptions.
  • Glow plugs and block heaters can help improve diesel engine performance in cold weather.
  • Fuel additives and regular maintenance can also help keep diesel engines running smoothly in cold weather.

Understanding Diesel Engines

Diesel engines are a popular choice for vehicles and equipment that require high power and efficiency.

Unlike gasoline engines, diesel engines use compression instead of spark ignition to ignite the fuel. This process is known as combustion, which produces the engine’s power.

High torque and fuel efficiency

Diesel engines are known for their high torque and fuel efficiency. This is because diesel fuel has a higher energy density than gasoline, which contains more energy per unit of volume.

It allows diesel engines to produce more power for the same amount of fuel, making them ideal for heavy-duty applications.


When it comes to diesel engines, compression is vital. The compression ratio of a diesel engine is much higher than a gasoline engine, allowing the fuel to ignite without needing a spark.

This makes diesel engines more reliable and easier to maintain than gasoline engines. However, cold weather can have a significant impact on diesel engine performance.

Temperature drops

When the temperature drops, diesel fuel can start to gel or solidify, disrupting normal fuel flow and causing difficulties in starting the engine or hindering its performance.

It’s generally considered too cold for a diesel truck when the temperature drops below 15°F (-9.5°C).

It’s essential to take extra precautions in cold weather to ensure your diesel engine performs at its best. Some measures include using a battery warmer, an oil warmer, or a block heater to keep the engine warm.

Regular maintenance, such as checking coolant regularly with a hydrometer, can also help prevent issues in colder temperatures.

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The Impact of Cold Weather on Diesel Engines

When temperatures drop, diesel engines can struggle to start. The combustion process requires heat, and if the engine is too cold, generating the necessary heat to ignite the fuel can be difficult.

It can result in poor combustion, leading to black smoke emissions and engine damage over time.

Thicker and form wax crystals

In extreme cold, diesel fuel can also become thicker and form wax crystals, causing fuel filters to clog and engines to stall.

To prevent this, use winter blended fuel, less likely to gel, and store full portable fuel cans in a temperature-controlled area to avoid condensation.

Check for White smoke.

White smoke can also be a sign of poor combustion in cold weather. It could indicate that the fuel is not being burned efficiently, leading to harmful emissions and increased wear and tear on the engine.

To avoid these issues, use a battery warmer, an oil warmer, or a block heater to keep the engine warm. Diesel engines should not be operated below -5° C (23° F).

At such temperatures, it may be possible for the engine to start and run initially, but performance and reliability may be significantly degraded due to cold start problems.

Effects on Diesel Fuel and Oil in Cold Weather


When the temperature drops, diesel fuel can become thicker and even form crystals, a phenomenon known as gelling.

It can cause problems with fuel flow and lead to engine failure. Gelling occurs when the paraffin wax in diesel fuel solidifies, clogging fuel filters and lines.

The fuel pour point, or the lowest temperature at which the fuel can still flow, is essential to consider when dealing with cold weather.

Chemical characteristics

In addition to gelling, cold weather can also affect the chemical characteristics of diesel fuel and engine oil.

Cold temperatures can cause fuel and oil to thicken, resulting in decreased viscosity and reduced fuel efficiency.

Your engine may require more fuel, leading to higher costs and reduced performance.

It is essential to use diesel fuel with a lower pour point and to regularly replace fuel and oil filters, to prevent gelling and other cold weather-related issues.

Additionally, using engine oil with the appropriate viscosity rating for cold weather can help ensure optimal engine performance.

The Role of Glow Plugs and Block Heaters

Heating the internal combustion chamber

Glow plugs work by heating the internal combustion chamber to suit conditions for compression and ignition.

Waiting on the glow plugs is essential to heat the combustion chamber adequately. If the glow plugs are cold, fuel sprayed on the semi-heated plugs can cause the diesel fuel to gel up and stick to the cylinder heads.

Keep the engine block warm.

Block heaters, on the other hand, are designed to keep the engine block warm, which helps ensure that the engine is at the correct operating temperature when you start it.

It can be essential in freezing weather, as diesel engines can be five times harder to start at 0°F (-17°C) than at 80°F (26°C).

If you’re wondering whether you need a block heater, the answer is simple: it depends on how cold it is outside.

Generally, if the temperature drops below 20°F (-7°C), you should consider using a block heater to ensure your engine starts smoothly.

Give the engine time to warm up.

In addition to using glow plugs and block heaters, it’s also essential to give your engine time to warm up before you start driving.

This can help prevent unnecessary wear and tear on your engine and ensure it operates at peak efficiency. A good rule of thumb is to let your engine run for at least 10 minutes before you start driving.

Properly warming your diesel engine can help ensure it starts smoothly and operates at peak efficiency, even in extremely cold weather.

Battery Performance in Cold Weather

When the temperature drops, your diesel engine’s battery performance can be affected.

Batteries can lose up to 60% of their power at 0°F, leading to electrical failure and difficulty starting your engine. Read this to learn how long to make your car batteries last longer!

To ensure your battery is working correctly, use a multimeter to check its voltage when the engine is running.

The voltage should measure between 13.7 and 14.7 volts. If the reading is below 12.6 volts, replacing the battery is time.

It’s also essential to note that if you have one battery that is three years old and another that’s eight years old, it’s best to replace both batteries.

Uneven battery ages can lead to electrical issues and reduced performance.

To keep your battery functioning correctly in cold weather, consider the following tips:

  • Keep your battery clean and free of corrosion.
  • Use a battery blanket or heater to keep it warm.
  • Turn off all electrical accessories when starting your engine.
  • If your battery is over three years old, have it checked by a professional.

Fuel Additives and Their Benefits

Cold flow properties

Diesel fuel gels at low temperatures can cause fuel starvation, loss of engine power, and stalling. Fuel additives can prevent these issues by improving the fuel’s cold flow properties.

Improve performance and efficiency.

Adding a fuel additive to your diesel fuel can also help improve engine performance, increase fuel efficiency, and reduce emissions.

Fuel additives can clean the fuel system, lubricate injectors and pumps, and protect against corrosion.

Prevent water buildup

Different fuel additives are available, each with its benefits. For example, some additives can prevent water buildup in the fuel system, while others can improve cetane levels, leading to better engine performance.

Choosing a suitable fuel additive and following the manufacturer’s instructions when using it is essential.

Using too much of an additive or misusing it can cause damage to the engine or fuel system.

Fuel additives can be valuable for diesel engine owners in cold temperatures. Fuel additives can help ensure your diesel engine runs smoothly and efficiently year-round by improving cold flow properties, engine performance and reducing emissions.

Starting a Diesel Engine in Cold Weather

Starting a diesel engine in cold weather can be challenging, but you can make it easier with the proper techniques.

Here are a few tips to help you start your diesel engine in cold weather:

  • Use glow plugs or block heaters to warm up the engine before starting it. It will help the engine reach its operating temperature faster, making starting easier.
  • Use a starting fluid if necessary, but do not overuse it, as it can damage the engine. Follow the manufacturer’s instructions carefully when using starting fluid.
  • Once the engine starts, allow it to idle for a few minutes to warm up and circulate the oil. This will help prevent engine damage and ensure smooth operation.
  • Avoid revving the engine excessively when starting it. Instead, keep the rpm low until the engine has warmed to its operating temperature.

By following these tips, you can start your diesel engine in cold weather more efficiently and avoid damaging it.

Maintaining Diesel Engines in Cold Weather

Diesel engines require special attention when the temperature drops to keep running smoothly. Here are some tips to help you maintain your diesel engine in cold weather:

  • Keep your fuel tanks and cans filled to prevent condensation from forming. Water in your fuel system can cause serious problems, especially in cold weather.
  • Use weather-appropriate fuels like winter diesel to prevent gelling and waxing. These fuels have lower cloud and pour points and are more resistant to cold weather.
  • Check your fuel filter and replace it if necessary. A clogged fuel filter can restrict fuel flow and cause starting problems.
  • Inspect your fuel lines and hoses for cracks and leaks. Cold weather can cause rubber to become brittle and crack, leading to fuel leaks.
  • Ensure your diesel exhaust fluid (DEF) tank is complete and the fluid is fresh. DEF can freeze and cause damage to your engine if it’s not maintained correctly.
  • Check your coolant level and ensure it’s the right mixture for the temperature. Too much water can cause your coolant to freeze, while too much antifreeze can reduce the coolant’s ability to transfer heat.
  • Use synthetic oil to improve flow and lubrication in cold weather. Synthetic oils are more resistant to cold temperatures and offer better wear protection than conventional oils.

These tips help ensure your diesel engine starts and runs smoothly in cold weather. For more information on maintaining your diesel engine, visit NAPA Online.

Comparing Diesel and Gasoline Engines in Cold Weather

As highlighted above, starting diesel engines in cold weather has a more challenging time than gasoline engines. It is five times harder to start a diesel engine at 0°F (-17°C) than it is to start one at 80°F (26°C).

One of the main reasons is that diesel fuel can turn into a gel-like substance in cold temperatures, causing it to clog fuel filters and prevent fuel flow to the engine.

On the other hand, gasoline engines have a much easier time starting in cold weather because gasoline is less likely to turn into a gel-like substance in cold temperatures.

Gasoline-powered engines

Gasoline-powered engines also have a more straightforward starting process than diesel engines. Gasoline engines use a spark plug to ignite a mixture of air and fuel in the engine’s cylinders, while diesel engines rely on compression to ignite the fuel.

Another factor to consider is the exhaust gas produced by diesel and gasoline engines in cold weather. Diesel engines produce more exhaust gas than gasoline engines, which can cause problems in cold weather.

The moisture in the exhaust gas can freeze and block the exhaust system, leading to reduced engine performance and potential damage to the engine.

Diesel engines have more difficulty starting and producing exhaust gas in cold weather than gasoline engines. If you live in an area with cold winters, you must take extra care of your diesel engine to ensure it starts and runs smoothly.

Frequently Asked Questions

What is the lowest temperature for winter diesel?

Winter diesel is formulated to work in temperatures as low as -15°F (-26°C) without gelling or solidifying. However, some winter diesel blends have a lower cold filter plugging point (CFPP) and can work in even colder temperatures.

How cold is too cold for a diesel engine in winter?

Diesel engines can be harder to start in cold weather, significantly below-freezing temperatures. It’s generally considered too cold for a diesel engine when the temperature drops below 15°F (-9.5°C).

The diesel fuel can gel or solidify at this temperature, potentially disrupting normal fuel flow and causing difficulties in starting the engine or hindering its performance.

At what temperature does diesel freeze?

Diesel fuel typically starts to solidify at around 17°F (-8°C) to 19°F (-7°C). However, the exact temperature at which diesel fuel freezes depends on the fuel’s composition and the presence of additives.

How to start a diesel in cold weather without a block heater?

Starting a diesel engine in cold weather without a block heater can be challenging, but you can do a few things to make it easier.

First, make sure your battery is fully charged. Second, use a fuel additive to improve the flow of diesel fuel. Third, use synthetic oil that flows better in cold temperatures. Finally, consider using an engine block heater or a battery warmer to keep your engine warm.

Diesel fuel gelling temperature chart?

A diesel fuel gelling temperature chart shows the lowest temperature at which diesel fuel can start to gel or solidify. The chart can help determine if your diesel fuel suits current weather conditions. You can find diesel fuel gelling temperature charts online or from your supplier.

Are diesel engines bad in cold weather?

Diesel engines can be harder to start in cold weather, but they are generally reliable and efficient in cold climates. Diesel engines can run smoothly in cold weather with proper maintenance and care. However, using the right fuel and following the manufacturer’s recommendations for cold weather operations is essential.


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