What is Blow by on a Diesel

Blow by on a diesel engine is when the engine’s combustion process allows gases to escape past the piston rings and into the crankcase. This can cause a reduction in engine performance and damage to various engine components if left untreated.

When an engine runs, the pressure from combustion forces the piston down into the cylinder. However, not all of the pressure is converted into motion. Some pressure escapes past the piston rings and into the crankcase, creating what is known as “blow by”.

The blow by problem is common in diesel engines, regardless of whether they are new or old. Blow by can lead to a decrease in engine power, increased fuel consumption, higher levels of exhaust emissions and even engine damage leading to expensive repairs. Controlling blow by is possible via maintenance like replacing the piston rings or other methods.

What is Blow by on a Diesel

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Causes Of Blow By

Blow by is when diesel fuel, oil or air from the combustion of fuel leaks past piston rings into the engine crankcase. This can cause engine damage and requires careful monitoring. The primary cause of blow by is wear and tear from the engine, as well as lack of maintenance.

When the engine is not properly cared for or the air filter is dirty, dust and particles can accumulate in the engine, leading to increased wear and tear. This can cause blow by and negatively affect vehicle performance. Another critical reason for blow by is inadequate lubrication, which can cause increased friction and heat.

In addition, a malfunctioning pcv valve can also cause increased pressure in the engine and lead to blow by. Proper maintenance, regular inspection, and replacing faulty parts can help prevent blow by in diesel engines.

What Is Diesel Blow By?

Symptoms Of Blow By

Blow by on a diesel engine happens when there is an excessive amount of oil and gas that escape past the piston rings, causing a buildup of pressure in the crankcase. This can result in symptoms such as oil leaks, blue smoke from the exhaust, and decreased power.

These symptoms can be a sign of a serious issue with the engine and should be addressed promptly. Regular maintenance, including oil changes and replacing worn parts, can help prevent blow by. If you experience any of these symptoms, have your engine inspected by a qualified mechanic.

It is important to diagnose and fix any issues promptly to avoid permanent damage to the engine.

Fixing And Preventing Blow By

Blow by on a diesel engine is when combustion gasses escape from the combustion chamber and enter the crankcase. This often causes a loss in power, poor fuel economy and increased oil consumption. To fix and prevent blow by, it’s important to regularly maintain the engine, replace worn or damaged parts, ensure proper installation and tighten any loose connections.

Additionally, using high quality oil and avoiding overloading the engine can also help in preventing blow by. By following these guidelines, you can ensure your diesel engine runs smoothly and efficiently, without any blow by issues.


As a diesel engine owner, understanding the concept of blow by is crucial in maintaining the engine’s overall performance and longevity. Blow by is a common issue amongst diesel engines and can cause various complications if not addressed on time.

In this article, we’ve covered what blow by is, its causes, symptoms, and methods of prevention. By ensuring the engine oil is changed regularly, maintaining recommended oil levels, and adhering to the manufacturer’s recommendations, you can significantly reduce the risk of blow by in your diesel engine.

Blow by is a problem that should not be ignored. It is essential to recognize the symptoms early on and take the necessary measures to address it. By being knowledgeable about blow by and diesel engine maintenance, you can save yourself time, money, and the risk of costly damages.

Keep your engine healthy and performing at its best, and enjoy all the benefits that come with owning a diesel engine.