You probably don’t know what engine blow-by is. Many car owners have never even heard of the term before. Let’s change that today. Engine blow-by is a serious issue that can cause a lot of damage to your car if it’s not taken care of. In this article, we will explain engine blow-by, the symptoms to look for, and how to fix it.
Engine blow-by occurs when combustion gases escape past the piston rings into the crankcase. Excessive oil consumption, blue exhaust smoke, decreased power, and increased engine noise are all symptoms of engine blow-by.
Table of Contents
What is Engine Blow By? What Does it Mean?
Before we dwell on what is engine blow-by and what does it mean? It is important to understand the basic working of an internal combustion engine. An internal combustion engine works on the principle of igniting a fuel-air mixture inside the engine’s compression chamber using a spark plug (SI Engine) or without that (CI Engines). The expanding gases from the burning mixture push the piston towards the crankshaft. This up and down movement of the pistons turns the crankshaft during the engine’s power stroke which in turn rotates the wheels via a transmission system.
Now that we have understood how an internal combustion engine works let’s get back to our topic – engine blow-by. Engine blow-by is a condition where some of the gases that are supposed to be pushed out of the cylinders escape past the piston rings into the crankcase. These gases are a mixture of water vapor, carbon dioxide, unburned fuel, and air. This can cause several problems, including increased oil consumption, loss of power, and overheating. In severe cases, it can even lead to engine failure.
Blow-by is not a new phenomenon and has been there since the first internal combustion engine was built. However, it became more widely talked about only when high-performance aircraft engines were developed. In these engines, blow-by was found to cause deterioration and corrosion of engine parts.
Today, with better engineering and design, blow-by in modern engines is not as big an issue as it was in those early days. However, it is still something that needs to be monitored.
What are the Negative Impacts of Blow by on Your Car?
The major negative impact of engine blow-by on your car is increased wear and tear on the engine. This can lead to decreased performance and fuel efficiency, as well as increased emissions. In severe cases, it can also cause engine damage.
Another potential negative impact of blow-by is oil contamination. When blow-by occurs, it can force oil and other contaminants into the combustion chamber. This can lead to deposits forming on valves and other engine components, which can eventually cause engine failure.
Overall, the negative impacts of engine blow-by can be significant. If you suspect that your car is suffering from blow-by, it is important to have it checked out by a qualified mechanic as soon as possible. Ignoring the problem could lead to serious engine damage or even failure.
How Much Blow-by is Normal? How to Measure Engine Blow-by?
Normal blow-by levels will vary depending on the specific engine design, but in general, newer engines will have less blow-by than older engines. It is not abnormal for an engine to have blow by somewhere between 2 to 3 cfm. A bigger engine can have a higher blow-by.
Measuring blow-by can be a tricky task. Let us divide it into two parts, use of manometer and then convert that manometer reading into cfm (compatible units)
- Measuring blow-by can be done with a tool called a manometer, which measures pressure differential.
- To use a manometer, attach one end to the crankcase vent and the other to a vacuum source.
- Start the engine and let it idle for several minutes.
- Then, turn off the engine and read the manometer.
- Note down the reading in inches of water.
Now the second task is how to convert this reading into compatible units. It involves some nasty mathematical equation but let me make it easy for you:
- You can easily find correlation charts between inches of water and velocity inside the duct in feet per second.
- Find velocity from that cart against the value you noted in inches of water.
- Take that velocity reading and multiply it by 3.14.
- Now multiply this number with the radius of your manometer duct.
- Again multiply the result with the radius of your manometer duct.
- At last, multiply it by 60, and the final result is the value of engine blow-by in cfm.
- As a thumb rule, divide your engine’s horsepower by 48 to get an exact range for normal blow-by.
- For example, Toyota Yaris with 130 hp will have 130/48 = 2.7 cfm blow by normally.
Symptoms of Engine Blow By
As we have seen, engine blow-by can cause several problems. But how do you know if your car is suffering from it? Here are some symptoms to look out for:
- Blue Smoke From Exhaust
- Knocking Noise From Engine Bay
- Increased Fuel Consumption
- Milky Exhaust Fumes
- Engine Misfires
- Sooty Substance on Engine Head
- Poor Performance of Engine
- Engine Failure
Let us see these symptoms in a bit detail:
1. Blue Smoke From Exhaust:
Blue exhaust smoke is typically an indication of engine blow-by. When an engine experiences blow-by, it means that combustion gases are escaping past the piston rings and into the crankcase. This can cause a build-up of pressure within the crankcase, eventually leading to engine damage.
If you see blue smoke coming from your car’s exhaust, it is important to have it checked out by a qualified mechanic as soon as possible.
2. Knocking Noise From Engine Bay:
Another symptom of engine blow-by is a knocking noise coming from the engine bay. This is caused by the build-up of pressure within the crankcase, which can eventually lead to engine damage. It’s actually quite normal to hear a knocking noise from around the valve cover area as a result of an engine blow-by. This is because when the piston moves up and down, it creates a vacuum that pulls air through the gaps in the piston rings. As the air is forced through these tiny spaces, it collides with the piston and causes a knocking noise.
Although there can be multiple reasons for knocking noise from the engine. However, if you only hear it when the engine is under load or working hard, it’s most likely due to blow-by. If you hear knocking at idle, it could be due to a mechanical issue such as worn piston rings or damaged bearings. In either case, it’s best to get the vehicle checked out by a qualified mechanic to diagnose the root cause of the problem.
3. Increased Fuel Consumption:
One of the most common symptoms of engine blow-by is increased fuel consumption. When an engine burns fuel, it produces energy that turns the crankshaft. However, due to blow by, some of this energy is used to push combustion gases through the gap between the rings and the cylinder walls.
Whenever blow by allows some gases from the combustion chamber to escape into the crankcase, output power to fuel consumption is decreased. Hence, the reduced fuel efficiency. Over time, these escaping gases can build up in the crankcase and cause problems. Perhaps most importantly, they can increase your fuel consumption.
4. Milky Fumes:
When you open the oil filler cap or oil pan and see milky white fumes, it indicates water in the oil. This generally happens when there is condensation in the crankcase due to blow-by gases. The water vapor present in these gases (air-fuel mixture) can mix with the engine oil and form an emulsion. When this mixture gets hot, it turns into a white milky substance. If you see this substance on your dipstick or oil filler cap, it indicates that your car is suffering from an engine blow-by.
5. Engine Misfires:
Another symptom of engine blow-by is engine misfires. The main reason is that the pressure from the blow-by can cause the spark plugs to become fouled or damaged. If the spark plugs cannot function properly, the engine will misfire. In addition, the pressure from the blow-by can also damage the piston rings. When the piston rings are damaged, they will no longer be able to seal the combustion chamber correctly. This will also cause engine misfires.
6. Sooty Substance on Engine Head:
If you see a black sooty substance on the engine head, it’s an indication of oil burning. This generally happens when there is too much blow-by happening in the engine. When there is too much blow-by, it means that the piston rings are not able to seal the combustion chamber correctly.
This will cause some engine oil to be drawn into the combustion chamber and burned along with the fuel. The sooty substance is just engine oil that has been burned. If you see this on your engine, it indicates that you have a problem of engine blow-by.
7. Poor Performance of Engine:
If you notice that your engine is not performing as well as it used to, it could be due to blow-by. One of the most common ways an engine blow-by can cause poor vehicle performance is by causing the engine to run lean. When an engine runs lean, it means that there is not enough fuel being burned in the combustion chamber. This can lead to a number of problems, including decreased power.
Whereas, as a result of the blow by, small amounts of gases and vapors escape past the piston rings and into the crankcase. These vapors contain hydrocarbons and other pollutants that can negatively affect both air quality and your vehicle’s performance. This can also cause deposits to build up on engine components. These deposits can restrict airflow and negatively affect the engine performance.
8. Engine Failure:
One of the most serious consequences of engine blow-by is engine failure. When there is too much blow by happening in an engine, it can cause the piston rings to break. If the piston rings break, it will cause the pistons to start moving up and down in the cylinders. This will cause a lot of damage to the engine and can eventually lead to engine failure.
What Cause Engine Blow by?
There are a few different things that can cause an engine blow by. The most common causes are explained below:
1. Engine Manufacturing Defects:
A variety of factors cause blow-by during the engine manufacturing process. Poor machined surfaces, incorrect piston-to-cylinder clearances, and poor quality control can lead to blow-by. One installation or manufacturing can occur if the piston rings are not properly installed. This can cause the rings to leak, which will allow oil and other fluids to enter the combustion chamber.
Another way is if the valve seals are not properly installed, which can also cause oil and other fluids to enter the combustion chamber. Also, if there are any cracks or holes in the engine block itself, this can also cause blow-by. These manufacturing defects can ultimately lead to increased engine wear, reduced performance, and eventually engine failure.
2. Damaged Cylinder Walls:
If the cylinder walls become damaged, it can also cause the engine blow by. The most common way cylinder walls become damaged is by wear and tear. Over time, the friction between the piston and the cylinder wall wears down the material of both surfaces. This process is accelerated by high temperatures and pressures, as well as by debris and contaminants in the engine oil. Eventually, the cylinder wall becomes thin and weak and starts to develop cracks.
In addition, if the engine overheats frequently, this can also cause the cylinder walls to become damaged. Another way that cylinder walls can become damaged is from corrosion. This is most commonly seen in engines that have been sitting for long periods without being used. The acids in engine coolant can eat away at the metal of the cylinder walls, causing them to become thin and weak.
Last but not least, cylinder walls can be damaged by impact. This can happen if a piece of debris gets into the engine or if the engine suffers a sudden shock (such as from a car accident). When the cylinder wall is hit, it can develop cracks or even shatter.
3. Worn Out Piston and Piston Rings:
There are several reasons why engine blow by can occur, but the most common cause is worn-out piston rings or pistons. When these parts wear out, they allow oil and other fluids to leak past them and into the combustion chamber. This can cause a build-up of pressure in the chamber, eventually leading to the engine blow by.
How to Prevent Engine Blow-by?
Now that you know what engine blow-by is and what causes it, you’re probably wondering how you can prevent it. There are a few things that you can do to help prevent engine blow-by.
1. Follow Maintenance Schedule:
One of the best ways to prevent engine blow-by is to follow the maintenance schedule for your vehicle. This will ensure that all of the parts in your engine are kept clean and lubricated. It is also important to make sure that you change your oil regularly. Dirty oil can cause a build-up of deposits on engine components, which can eventually lead to blow-by.
Another important part of following the maintenance schedule is checking your engine regularly for any signs of wear or damage. This way, you can catch any potential problems before they cause serious damage to your engine.
2. Ensure Crankcase Ventilation:
Another way to prevent engine blow-by is to ensure that your engine has proper crankcase ventilation. This ventilation system helps reinject blow-by gases into the combustion chamber, where they can be burned off.
If your engine does not have proper crankcase ventilation, blow-by gases will build up in the crankcase and eventually cause pressure to build up. This can lead to oil leaks, as well as engine damage.
3. Use High-Quality Fuel:
A good way to prevent engine blow-by is to use high-quality fuel. This fuel will help to keep your engine clean and free of deposits. It will also help improve your engine’s performance and extend its life.
How Can You Fix the Problem of Engine Blow-by? (+Fixing Cost)
If you have an engine blow-by, there are a few things that you can do to fix the problem. Some potential solutions are discussed below:
1. Flushing Oil Concentrate:
If you have an engine blow-by, one potential solution is to flush oil concentrate through your engine. This is because the oil flush helps to clean out any build-up of contaminants that may be causing the problem.
Additionally, flushing oil concentrate can also help to clear any engine sludge. It is generally a fairly inexpensive procedure. You can easily find oil concentrate flush at most auto parts stores. It will cost you between $100 and $150.
2. Replace Piston Rings:
If worn-out piston rings cause your engine blow-by, you will need to replace them. Over time piston rings can become worn or damaged, and this can cause the engine blow by. Replacing piston rings is one of the best ways to solve the problem of engine blow by.
New piston rings will provide a tighter seal between the piston and cylinder wall and help prevent blow by gases from escaping into the combustion chamber. This will help to improve engine performance and efficiency and will extend the life of your engine.
Replacing piston rings is one of the toughest and most expensive problems. On average, you can expect to pay between $1,200 and $4,000 for the parts and labor. However, if you have a luxury vehicle, the cost could be closer to $5,000.
Engine blow-by is a problem that can cause various issues for your vehicle. It is important to be aware of the symptoms of engine blow-by and to have your engine checked regularly for any signs of wear or damage.
Additionally, you can help prevent engine blow-by by following the maintenance schedule for your vehicle, using high-quality fuel, and ensuring that your engine has proper crankcase ventilation.
Frequently Asked Question
What is blow-by on diesel engines?
The blow-by on a diesel engine is the process where hot gases from the combustion chamber escape past the piston rings and into the crankcase. This can cause a build-up of pressure in the crankcase, leading to engine damage. To prevent this, many diesel engines have a breather system that allows these gases to escape before they can cause harm.
Are diesel fuel engines more prone to blow-by issues?
Yes, a diesel engine is more prone to blow-by issues because it has a higher compression ratio than gasoline engines. This higher compression ratio means the gases in the combustion chamber are under more pressure, which can cause them to escape past the piston rings and into the crankcase.
Is it safe to drive with engine blow-by symptoms?
If you’re noticing any blow-by symptoms, it’s best to get your car checked out by a mechanic as soon as possible. While it may be safe to drive with some blow-by, it’s not something that should be ignored. Left untreated, engine blow-by can lead to serious engine damage.