Diesel Knocking When Cold - Why? And What Can You Do with This?

Diesel-powered cars are renowned for their efficiency, slower depreciation, and low carbon emissions compared to gasoline cars. Yet, they also have their drawbacks. Here we want to consider one such drawback, diesel knocking in cold weather. Diesel knocking, also called pinging or detonation is a clattering or rattling sound linked to abnormal combustion in diesel cars. Knocking in diesel engines is not uncommon.

Diesel engine problems highlights

• Level of importance:Medium
• Commonreasons:Age and mileage, aggressive driving, poor maintenance
• DIY inspection:In most cases, impossible
• DIY repair:Impossible
• Price for repair:$650 - $1,500
• Can you drive?Depends on the issue
• Ways to fix:Replace the worn-out parts, professionalrepair is usually possible only

How Do Diesel Engines Work?

There is some semblance to how gasoline and diesel engines work since they are both internal combustion engines. But there is still a notable difference between gasoline and diesel cars. Unlike gasoline engines that rely on a spark to ignite a compressed mixture of fuel and air, diesel engines rely on a compression-igniting system to turn diesel into mechanical energy for locomotion.

Diesel engines only compress air and not fuel. Air is introduced during the intake stroke and compressed during the compression stroke. Then, diesel fuel gets injected into the cylinder after air compression. Since diesel engines do not use a spark plug for ignition, the heat from the compressed air causes the fuel to ignite spontaneously.

The spontaneous ignition leads to a quick release of chemical energy and a sudden rise in cylinder pressure. In most diesel engines, diesel fuel tends to be injected towards the end of the compression stroke. The combustion process is exact and requires fuel to enter the cylinders at the right time. A delay in the combustion process may lead to sudden high pressures above the piston, which produce a knocking sound. In more detail, the high pressure causes the piston to strike against the crankshaft's walls. Diesel knocking noises may sound like clattering or rattling.

How Can Cold Contribute to Knocking in Diesel Engines?

As already stated, diesel engine knocking is not unusual. In fact, manufacturers of diesel engines have to account for the spontaneous increases in pressure that cause the knocking sound in the design and development of the engine. So, diesel knocking can happen as part of routine combustion. However, the knocking should only last briefly and stop under 15 minutes after starting the engine. Outside of routine combustion, other things, including cold weather, can make the engine knock longer and more intensely than usual.

One reason diesel engines knock more at low temperatures is the increased viscosity of the fuel. Viscosity refers to the stickiness or thickness of fluids. The viscosity of fluids affects how they move and flow. Different liquids have differing viscosities. Diesel fuel is denser and contains more oil than gasoline/petrol. However, low external temperatures can make the already thick fuel even thicker. As such, more viscous diesel fuel will take longer to pass through your vehicle's fuel system and into the engine's cylinders for combustion.

Remember, the ignition process in all internal combustion engines needs to be precise. So, suppose the diesel fuel becomes viscous due to low temperatures or cold. In that case, it might take longer for the already compressed air to ignite the fuel as it enters the cylinders. This situation may cause your diesel engine to knock.

Further, knocking in diesel engines may occur because the compressed air is not hot enough for combustion. If the weather is too cold, the compression process in a diesel engine may struggle to raise the temperature of the air to a level where it can ignite the fuel immediately after it enters the cylinders. So, for an engine to operate optimally, it needs to warm up quickly. Yet cold weather conditions can prevent this from happening.

Low oil levels can worsen the combustion heating problem because oil circulation throughout the engine helps to provide warmth for its parts. In such a case, the engine may produce that knocking sound over and again.

Some engine designs, as well as fuel injector mechanisms, are also more prone to knocking than others. For instance, indirect fuel injection systems are less prone to engine knocking than direct fuel injection systems. Also, electric-powered common-rail direct fuel injection systems cause fewer engine knocks. As a result, cold weather will induce or increase engine knocks in some cars more than others because of the engine design and fuel injection mechanism.

Besides routine combustion-induced knocking and cold weather, some of the other things that can cause diesel engine knocking include:

• Valve leak or damage
• Inappropriate fuel grade
• Exhaust leak
• Broken bolts
• Issues with the fuel injectors

Even though diesel engine knocks are not unusual in cold weather, sustained knocking after the engine warms up can cause significant problems for the engine and driving performance. Possible side effects of diesel engine knocking include:

• Noisy engine
• Black or white Smoke
• Thermal stress cracks in piston crowns
• Ring land fracture
• Piston crown fracture or distortion
• Crankshaft damage

Preventing And Managing Diesel Knocking in Cold Weather

There are some things you can do to help with cold-induced diesel knocking. We discuss them below.

1) Warm Up the Engine

The compressed air's temperature in the cylinders may not get hot enough to ignite the fuel in cold weather. So, starting up the machine before you attempt to drive the car can prevent engine knocking. Try to warm up the engine for up to five minutes before operation.

2) Keep Your Vehicle in A Warm Place

An enclosed area, such as a covered garage, can reduce help reduce the effect of cold on an engine. Garages are usually up to 20 degrees warmer than outside. Also, you can use heating tools to keep your engine warm, especially overnight or whenever you know you will not use the car for many hours. Oil warmers, battery warmers, diesel-fired coolant heaters, and block heaters will help keep the engine warm.

3) Make Use of High-Quality Fuel and Fuel Additives

Like engine oil, diesel fuel can thicken if exposed to freezing weather. If the fuel is too thick, it will take longer to reach the cylinder, creating a delay in combustion and leading to engine knocks. Diesel fuel gelling occurs at very low temperatures, below 10 degrees Fahrenheit (-12 degrees Celsius).

Winter diesel fuel or alpine diesel are fuels that can help in cold or winter conditions. The winter fuel moves faster and prevents cold starts and engine knocks.

Also, fuel additives contribute to improving the quality of fuel in vehicles. Even the most efficient diesel fuel winter blends can gel depending on how cold the weather gets. This can affect combustion. There are fuel additives designed to enhance combustion. Using such fuel additives will likely reduce diesel knocking. Many winter fuel mixes include fuel additives.

4) Maintain Fuel Injectors

Dirty or clogged fuel injectors can contribute to extended diesel knocking even without cold weather. Cold weather can make the problem more severe. Thus, getting the fuel injectors inspected and maintained regularly is imperative.

5) Change The Oil

Engine oil is critical for lubricating an engine and its moving parts. Diesel knocking can occur when the oil lubricating the valve filters becomes thick and pasty due to low external temperatures. Such a situation will prevent the oil from moving freely and introduce engine knocking with valvetrain components bouncing against each other. Besides lubrication, engine oil helps warm up the engine and enable combustion.

There are oils made explicitly for diesel engines to provide better lubrication for them that you can use. An additive is often added to diesel oils to help protect against engine knocking during cold weather. Also, lighter engine oils will circulate better in cold weather.

You should also ensure your engine's oil levels do not drop below the minimum required level.

Suppose engine knocking becomes too intense or persists for more than 15 minutes after starting your vehicle. In that case, you might have a more severe problem. In such a situation, contact your mechanic to inspect the problem thoroughly. Sustained engine knocking can damage components of the engine and even the engine in some cases.

Conclusion

While knocking in diesel engines is not unusual, cold weather can affect several things in your car and induce engine knocks. Cold weather can increase fuel and oil viscosity and limit the heat levels of compressed air. These situations can cause engine knocking in your diesel car. You can ease the cold-induced engine knocks by keeping your vehicle out of the cold and warming up your machine before use. Also, using high-quality diesel fuel and additives, among other things, will also help with the problem.

There is nothing extraordinary about diesel knocking in cold weather. However, knocking should stop after the engine runs for some time. Sustained knocking can cause severe damage. If your diesel engine continues to knock for a sustained duration, consult your mechanic for assistance.