Blowby in Engine (Symptoms, Causes, and Fixes)
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Blowby is a term used to describe the leakage of combustion gases, along with unburnt fuel and oil, from the combustion chamber of an internal combustion engine into the crankcase.
Blowby is an inevitable byproduct of the engine's combustion process. It occurs when some of the compressed air and fuel mixture in the combustion chamber leaks past the piston rings and into the engine's crankcase.
Blowby is a common problem in engines, especially in older or high-mileage engines, and can result in reduced engine performance, increased oil consumption, and engine damage.
Blowby can also cause the engine to produce excessive smoke and emissions, contributing to environmental pollution.
The engines have various devices, such as PCV (positive crankcase ventilation) valves and oil separators, which help regulate the pressure inside the crankcase and minimize the harmful effects of blowby.
Regular maintenance, such as oil changes and air filter replacements, can also help to reduce the occurrence of blowby and extend the life of an engine.
Table of Contents
What Causes Blowby in Engine?
There are several potential causes of blowby in engines, each of which can impact the engine's performance and health differently.
1. Worn Piston Rings
One of the most common causes is worn piston rings. Over time, the piston rings can become worn or damaged, preventing them from creating a tight seal between the piston and the cylinder wall.
This can allow gases and other combustion products to escape past the rings and into the crankcase, leading to increased oil consumption and reduced engine power.
2. Damaged Cylinders
Another common cause of blowby is damaged cylinders. When the cylinder walls become scored or damaged, they can no longer provide a smooth surface for the piston rings to glide against, which can lead to blowby.
This is due to various factors, including poor lubrication, overheating, or debris entering the engine.
3. Poor Ventilation Systems
Poor ventilation systems can prevent the crankcase from properly venting excess gases and pressure and high engine temperatures.
This can cause the piston rings to become distorted and lose their ability to create a tight seal.
4. Quality of the engine oil
Finally, the quality of the engine oil can also play a role in blowby. Using low-quality or improperly formulated engine oil can cause the piston rings to become gummed up or rusted, preventing them from creating a tight seal and leading to blowby.
Symptoms of Blowby in Engine
1. Excessive Oil Consumption
One of the most common symptoms of blowby is excessive oil consumption. When gases escape past the piston rings and into the crankcase, they can cause the oil to become contaminated and burned, leading to increased oil consumption.
If not addressed promptly, this can cause the oil level to drop quickly, leading to potential engine damage or failure.
2. Reduced Engine Power
Another symptom of blowby is reduced engine power. Gases escaping past the piston rings can reduce the pressure generated during the power stroke, leading to reduced power and acceleration.
This can be especially noticeable when accelerating from a stop or driving up steep hills or inclines.
3. Excessive Smoke
Excessive smoke is another common symptom of blowby. When combustion gases and other byproducts enter the crankcase, they can mix with the engine oil and create a thick, dark smoke often visible from the tailpipe.
This can signify that blowby is occurring and that the engine requires attention.
4. Poor Engine
The poor engine idle is another symptom of blowby. As combustion gases escape past the piston rings, they can create an uneven idle or cause the engine to stall. This can make it challenging to start the engine or keep running smoothly at low speeds.
5. Increased Engine Noise
Finally, blowby can also cause increased engine noise. As gases escape past the piston rings and enter the crankcase, they can create additional noise and vibration that can be noticed while driving.
How To Prevent Blowby
Preventing blowby in your engine is essential to keep your vehicle running smoothly and efficiently.
Blowby occurs when gases leak past the piston rings and into the crankcase, leading to decreased engine performance and increased wear on engine components.
Fortunately, there are several steps you can take to prevent blowby and keep your engine running strong.
1. Regular Maintenance
Regular maintenance is one of the most important things you can do to prevent blowby. This includes regularly changing the oil and air filter and checking and maintaining proper engine compression.
Keeping the engine clean and free of dirt and debris can also help prevent blowby by ensuring the proper functioning of engine components.
2. Use High-Quality Engine Oil
Ensure usage of high-quality engine oil that meets the manufacturer's specifications and can also help prevent blowby.
The right engine oil can reduce friction and wear on engine components, including the piston rings.
It can also help keep the engine clean and prevent deposits from forming, which can lead to blowby.
3. Avoid Overheating
Overheating can damage engine components and lead to blowby. To prevent overheating, ensure the engine is maintained correctly, including proper coolant levels and a functioning radiator. Also, avoid driving in high temperatures or stop-and-go traffic for long periods.
4. Address Engine Problems Promptly
If you notice any engine problems, such as increased oil consumption or a decrease in engine performance, it's essential to address them promptly.
Delaying repairs can lead to further damage and ultimately lead to blowby. Prompt attention to engine problems can also help prevent more costly repairs.
5. Don't Overwork the Engine
Finally, it's essential to work the engine properly. This means avoiding aggressive driving, towing heavy loads beyond the vehicle's capacity, and driving at high speeds for extended periods.
Overworking the engine can lead to increased wear on engine components, including the piston rings, which can contribute to blowby.
Blowby Testing
Blowby testing is a critical procedure used to evaluate the health and performance of internal combustion engines.
By conducting a blowby test, mechanics and engine technicians can identify potential problems early on and take corrective action before they escalate.
The engine is first warmed to operating temperature to perform a blowby test. Then, a pressure gauge is attached to the engine's oil filler hole, and the engine is run at idle speed.
The pressure reading is then recorded and compared to a reference chart to determine the engine's blowby level. This level is typically measured in terms of the percentage of air pressure that leaks past the piston rings and into the crankcase.
If the blowby level is too high, the piston rings will wear or get damaged, or the cylinder wall will be scored or out of round.
In some cases, excessive blowby may also be a cause of a faulty PCV (positive crankcase ventilation) valve or breather system. By diagnosing and addressing these issues, engine technicians can improve engine performance, reduce oil consumption, and extend the engine's life.
Blowby testing is significant for diesel engines, which are more prone to blowby than gasoline engines.
This is because diesel engines operate at higher compression ratios and typically have larger bore diameters, which can increase the likelihood of blowby occurring.
Additionally, diesel engines often work in harsh conditions, such as in heavy-duty trucks and construction equipment, which can accelerate wear on the engine components.
Blowby in Different Engine Types
However, the causes and effects of blowby can vary depending on the engine type in question.
Gasoline Engines:
Blowby is less common in gasoline engines than in diesel engines, but it can still occur. In most cases, blowby in gasoline engines is caused by worn or damaged piston rings or cylinder walls.
A clogged PCV valve or breather system can also cause it. Symptoms of blowby in gasoline engines include reduced engine power, increased oil consumption, and excessive smoke from the exhaust.
Diesel Engines:
Blowby is more common in diesel engines than in gasoline engines due to the higher compression ratios and larger bore diameters of diesel engines.
Additionally, diesel engines are common in heavy-duty applications that can accelerate wear on the engine components.
Symptoms of blowby in diesel engines include reduced engine power, increased oil consumption, excessive smoke from the exhaust, and oil leaks.
Two-Stroke Engines:
Blowby is a significant issue in two-stroke engines because these engines do not have separate intake and exhaust strokes like four-stroke engines.
This means that combustion gases are more likely to escape past the piston rings and into the crankcase.
Blowby in two-stroke engines can lead to reduced engine power, increased oil consumption, and poor exhaust emissions.
Four-Stroke Engines:
Worn or damaged piston rings or cylinder walls typically cause blowby in four-stroke engines.
A clogged PCV valve or breather system can also cause it. Symptoms of blowby in four-stroke engines include reduced engine power, increased oil consumption, and excessive smoke from the exhaust.
How To Fix Blowby
Repairing a blowby in an engine can be a complex process, as it depends on the underlying cause of the problem.
However, there are several steps that engine technicians can take to address blowby and restore engine performance.
Identify the Cause:
The first step in repairing blowby is to identify the underlying cause of the problem. In most cases, blowby is caused by worn or damaged piston rings or cylinder walls.
However, it can also result from a faulty PCV valve or breather system. By conducting a blowby test and inspecting the engine components, engine technicians can determine the cause of the problem and develop a repair plan.
Replace Worn or Damaged Components:
These components must get replaced if worn or damaged piston rings or cylinder walls cause blowby.
This typically involves disassembling the engine, removing the old piston rings or cylinder walls, and installing new ones. Sometimes, the entire engine may need total rebuilding to address blowby.
Clean or Replace the PCV Valve or Breather System:
These components must undergo cleaning or replacement if the blowby is from a faulty PCV valve or breather system.
The PCV valve regulates the flow of crankcase gases, and a clogged or malfunctioning valve can lead to blowby. Similarly, a clogged breather system can prevent proper crankcase ventilation, leading to blowby.
Perform Regular Maintenance:
Preventing blowby from occurring in the first place is often the best course of action. By performing regular maintenance on the engine, such as oil changes, air filter replacements, and spark plug replacements, engine technicians can help ensure that the engine operates efficiently and reliably over the long term.
