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.
What is Engine Blow by?
To understand blow-by, you need to understand how car engines work. Standard cars use internal combustion, a mixture of air and fuel gets sparked and essentially explodes with the power to move crankshafts and pistons.
Naturally, this process can have some unintended by-products. Specifically, the force of the combustion can push some of the pressurized gas, as well as any oil and still-liquid fuel mixed in with it, past the piston rings and into the crankcase where it does not belong.
This unwanted fluid that blows by the piston and into that crankcase is known as blow-by. Now, this in itself is not necessarily a problem, because your car has something called a PVC, Positive Crankcase Ventilation, system.
Without such a system, the combustion could pressurize the crankcase, which could divert power from the engine and lead to oil leaks. The PCV system works by pulling that blow-by back from the crankcase, where it ends up in the air intake.
Oil/gas blow-by in the air intake isn’t much better than blow-by in the crankcase, which is why you also have an air-oil separator in the system.
Unfortunately, this separator may not be 100 percent effective, especially over time, which is why you may eventually find yourself with a blow-by problem to deal with.
Types Of Blown Engines
What are the reasons behind a blown engine? As the term isn’t completely explicit about the specific fault, multiple failures can be connected to a blown engine. These are some of the more common ones:
#1. Blown Piston.
Piston problems are a common reason behind a blown engine. Interestingly enough, the piston rings are more prone to failure than the piston itself.
These metal rings secure the piston against the wall of the cylinder and keep the engine oil inside the crankcase, away from the combustion chamber. Moreover, they keep the combustion contained in the cylinder.
A blown piston could also mean a cracked or partially melted piston. Regardless of the reason, low compression is created in the cylinder.
#2. Hole In Engine Block.
A hole in the engine block warrants fear. It’s an obvious indicator of damaging impact, whether outside or inside. This is common in high-performance engines if something breaks inside the crankcase, like a connecting rod, and the result pushes the rod.
#3. Blown Rod.
A rod thrown by an engine rarely breaks the block. Although, it does cause internal damages. A “blown” or broken rod can result from high resistance or an over-revving engine.
Occasionally, the wrist pin connecting the piston and connecting rod falls out or breaks, and the rod moves around inside the machine, harming everything it comes in contact with.
#4. Seized Engine.
The first factor to consider with a seized engine is the lack of lubrication. But, that’s not always the only cause.
Oil starvation on moving metal surfaces and bearings generates overwhelming heat and friction, essentially welding the inner parts together. As the engine cannot rotate, it seizes.
#5. Broken Timing Chain Or Belt.
A steel chain or rubber belt ties the crankshaft to the camshaft. Its job is to maintain engine timing. If the timing chain or belt breaks, valves inside the cylinder head flop around.
In some engines, a timing belt break when the engine is running can make the valves negatively impact the pistons.
How to Check Engine Blow by?
It is effortless to make your blow by measuring tool. One of the recommended blow-by tools is a tee with a 15/64-in outlet. One end of the tee is connected to the end of the blow-by tube. On the other end of the tee outlet, put a manometer.
A simple manometer can be improvised by looping 6-feet of clear tubing into a ‘U’ with water in it. Measuring how high the water level rises using a tape measure, multiply the result by two, and then convert to LPMs. Roughly, 1” = 27 lpm.
Another easy way is blocking the blow by tube with a 0.5” pipe nipple with a cap. The cap should have a 15/64 hole drilled. Use a 3/8” id clear tubing with water inside slipped over an oil dipstick tube.
The other tubing end ought to remain open — Mark out the water level using a sharp-tipped marker while the engine is turned off.
A helper should help you start an already warm engine and then run the RPMs while marking at each stage, up to 2.2, 2.5, and 2.8k RPMs. Measure the distances from the first engine off the mark and then multiply each of the results by two.
You have to know how much blow-by is normal to know when your engine is not efficiently functioning.
Common Causes of Engine Blow-by
The most common causes of blow-by are worn-out piston rings, worn pistons, or damaged cylinder walls.
In some cases, you may mistake blocked crankcase ventilation for blow-by, so it’s good the check for clogged crankcase ventilation before checking for blow-by.
There are a few different things that could cause blow-by. Blow-by is a bad thing and often not easy or cheap to fix.
However, if you experience blow-by, you will want to check the crankcase breathing to make sure it’s not blocked first.
Here is a more detailed list of the four most common causes of engine blow-by:
#1. Worn out pistons.
Pistons are vital for moving the crankshaft. When the pistons start wearing out, they become smaller while the cylinder walls become larger.
Pistons are mostly made from aluminum, which happens to be a soft metal. When it wears out, it creates grooves in the piston while deposit accumulation occurs on the cylinder walls.
The fuel-air mixture soon finds its way into the crankcase. It can also be due to holes in the pistons from a knocking engine.
#2. Worn piston rings.
The piston rings are continuously being pushed back and forth in the cylinder wall, and with time they become worn and destroyed. This leads to leakage of gases, which causes blow-by.
Sometimes, the piston rings can get stuck, and this will often be solved by pouring some diesel into the cylinder and letting it sit for a while. With a little luck, they will come loose and seal against the cylinder wall again.
If not, the only way is to replace them, which is a very costly repair.
#3. Damaged cylinder walls.
The continuous movement of the pistons will, with time, lead to damaged cylinder walls. It can also come from damaged pistons or piston rings.
You can often notice damaged cylinder walls by listening for piston slap. Luckily, worn-out cylinder walls are not very common. If that happens, you either need to bore the cylinders to a bigger size and replace the pistons, or you have to replace the engine block.
#4. Faulty Crankcase ventilation.
In some cases, you can mistake blocked crankcase ventilation for blow-by. The crankcase ventilation’s job is to recycle blow-by into the intake again.
If the crankcase ventilation hoses are blocked, it will push it out from the oil cap once you open it, and you may think that your engine has a lot of blow-by.
Check the crankcase ventilation and make sure it is clear of any dirt.
Engine Blow by Symptoms
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.
Effects of Engine Blow By
Blow by effects most diesel engines. When the mixture of fuel and air escapes into the crankcase, pressure builds up, thus leading to a decrease in engine power. If the issue is not solved promptly, it leads to increased pressure that eventually destroys your engine.
In certain circumstances, the engine may knock or fail to start, which necessitates a replacement of the entire engine. A blown engine also leads to white or blue exhaust fumes, as this could mean that raw oil is being deposited into the combustion chamber.
Blow-by is also dangerous because it coats parts of the intake with both fuel and oil. After the cylinder walls and piston rings undergo degradation, more air, fuel, or moisture slips into the crankcase.
This, in turn, prevents the effective pushing of the piston down to enable the engine to produce enough output during the engine’s power stroke.
Most parts of an automotive engine are made of metal; hence expansion occurs due to heat.
A Subaru blow-by inhibits the overall performance due to the loss of compression. Moreover, the engines produce more irritating noise and may exhaust fumes that move out through the engine vents.
Blown engines also have increased fuel consumption. When fluids such as fuel, air, and moisture sip into the crankcase, contamination occurs on the oil, causing dilution.
In case there are any remnants of unburnt fuel, moisture, soot, gases, and Sulphur dioxide, they adhere to your engine’s compression chamber. These contaminants may cause extensive damage to your engine.
In simple terms, an engine blow-by decreases the efficiency of your engine, resulting in quite expensive and time-intensive repairs.
In the long run, if not promptly acted on, the result may be irreparable damage. Thus it is advisable to ensure proper maintenance of your engine to prevent a blow-by from occurring.
Blow by Treatment
A blow-By decreases the efficiency by increasing the consumption of fuel and oil in the engine.
Many a time, the entire engine has to be taken apart in order to solve the issue. However, there are certain things you could do to enable your motor vehicle to run for a while longer.
#1. Flushing Oil Concentrate.
You do not have to buy a new engine if it suffers from a blow-by. One of the most effective engine blow-by fixes is flushing an oil concentrate that cleans the engine.
The oil concentrate is usually mixed with hard-baked carbon. The mixture is run via the engine’s movable parts. It helps remove the engine sludge and effectively reduces blow-by and smoke, restores compression, and frees the piston rings.
Oil Treatment
Oil treatment helps reduce blow-by. As your vehicle’s engine ages, gaps are created in the movable parts. Combustion gases tend to leak from piston rings. This improves the engine’s performance.
While performing an oil treatment, you should avoid doing it if the engine is still hot. Also, ensure that the car is in parking gear and that the emergency brake is on. After you put the oil in the oil filter, start the engine and allow it to idle for a few minutes.
#2. FTC Decarbonized.
An FTC Decarbonized is also used to fix engine blow-by for diesel-driven vehicles. It is added into the diesel at every fill, and then you just drive the engine clean. The process of decarbonizing is quite gentle, progressive, and very efficient.
It also cleans DPFs and turbos. The more a blow-by is ignored, the more and more carbon accumulates in your engine. Excessive carbon leads to rapid wear. When you clean up the engine and maintain it that way, the risk of engine failure becomes almost insignificant!
If your vehicle’s blow-by problem does not resolve so it would be better to replace the piston rings or overhaul the Engine, this is the final treatment of your vehicle.
What is a normal blow-by?
Engine oil blow-by is when a mixture of air and fuel or combustion gases leaks between the engine’s pistons and cylinder wall into the crankcase. Engine blow-by can occur within both diesel and gas engines.
All engines have minor levels of blow-by, as piston rings aren’t completely watertight, even in new engines. For instance, a 12-liter engine in good condition may experience 1.5 cubic feet per minute (cfm) of blow-by under normal operating temperatures. That number increases to 3.5 cfm under colder temperatures.
Blowby happens when the internal combustion chamber of your engine forces contaminants such as air, fuel, and moisture past the piston rings and into the crankcase.
If your engine’s piston rings don’t have a good fit or aren’t well-sealed, they cannot contain the pressure produced from the combustion and will instead leak air-fuel mixture and contaminants.
Over time, as the engine’s pistons move up and down against the cylinders during normal engine operations, both parts wear away. The cylinders become wider, while the pistons become smaller.
The piston rings also wear away, making them less capable of maintaining a firm seal. As all the parts continue to grind against each other, these issues become more exaggerated, and the amount of blow-by can increase.
How to Identify and Check for Engine Blow By?
Your generator’s engine gives you numerous indications of it. Carrying out manual checks will reveal whether your diesel engine is experiencing any blow by.
If yes, you can then take effective measures to prevent blow by. To check it, you can carry out the following manual checks:
#1. Noises.
You can usually check the blow by based on the engine’s noise. It can be identified by loud or sputtering engine noises, which released fumes or exhaust clouds may follow.
#2. White Smoke.
One of the most evident signs of an engine blow by is White smoke billowing from the oil-fill tube or aperture on a valve cover. It also indicates that blow by is severe and needs immediate attention.
Test this by placing the oil filler cap on the tube or aperture upside down. There is too much crankcase pressure if it blows off right away.
#3. Oil film.
A coating of oil film surrounding the tube is another clear indicator. Engine blow by usually causes unburned gasoline to contaminate the oil and flow into the crankcase.
If there is too much blow by, the mixture may cause diesel to escape if it reaches the combustion chamber.
#4. Increased Oil and Fuel Consumption.
If your engine consumes more oil or fuel than usual, it might indicate that some of it leaks into the crankcase and creates blow by.
#5. Soot Buildup.
Blow by adds to increased incomplete combustion, which results in soot retention inside the cylinder walls. Excessive soot suggests the need for an oil change or may indicate more serious underlying issues.
#6. Rough Idling or Misfiring.
Blow by get in the way of critical engine functions. It makes it difficult for the generator to start. In some cases, it also makes it challenging to keep it running.
How To Diagnose A Blown Engine?
To know for sure that an engine is blown, you need expert advice. Unless you can pinpoint a hole in the engine block, there is no way to be certain of the engine’s condition without disassembling the bits and diagnosing everything separately.
A mechanic will have to check numerous things like the engine compression in every cylinder, signs of a misfire, leak inspection, and read diagnostic codes (if any) stored in the ECM.
Draining the engine oil or pulling the engine oil dipstick for inspection can be good reads (once you’ve figured out how to read oil level on dipstick).
Step 1
Check for big puddles of antifreeze or oil under the engine. Look for obvious damage symptoms like a large crack, a hole in the oil pan from the crankshaft or a rod, or a connecting rod sticking out of the block.
Step 2
Pull the dipstick and check for antifreeze or water in the oil. On a cold engine, remove the radiator cap and inspect for the opposite – a layer of oil floating on top of the antifreeze.
While either can suggest a failed head gasket, it could also mean there’s a gaping hole in the block between the water jacket and the oil galleys. There might be a hole in the cylinder wall too.
Step 3
Use the starter to turn the engine over. If the engine refuses to crank, use a socket wrench on an engine pulley to turn it over by hand.
Notice if you can hear any unnatural noises in the process. Suspect broken pistons, rods, or other serious problems if there are metallic, grinding noises as it turns.
Step 4
Take out all the spark plugs that can still be turned over, particularly if it turns over too fast. Examine the compression.
Many experts believe that an extremely low compression in all or some of the cylinders can be directly linked to a blown engine. Get a shop to do a leak-down test to understand how bad the damage is full.
Step 5
If your vehicle’s engine can still run but knocks or belches blue exhaust smoke, connect an oil pressure tester to it. Suspect worn and main rod bearings if the pressure is below average.
Make sure to calculate the total price of repairing the blown engine before confirming the repairs. It’s time to be brutally honest with yourself about the extent of the damages.
One thing can lead to another when rebuilding or replacing major engine parts. Get a good estimate of the total bill before starting.
How do you fix a Engine blow by?
If you really think that your car’s engine has a lot of blow-by, you might want to know how to fix it.
Fixing blow-by is often not very easy, as worn pistons or piston rings are usually at fault. However, there are some things you need to do to fix it.
#1. Clean Crankcase Ventilation.
The first thing you need to do is check your crankcase ventilation to make sure it is clear of sludge and dirt. Try to remove a hose and blow through it to make sure it’s clear. Also, check the PCV valve.
#2. Oil Treatment.
Sometimes it happens that the piston rings get stuck and will not seal against the cylinder walls. If you are lucky, this can be solved by pouring some diesel into the cylinders and letting them sit for a day or two.
#3. Replace Piston Rings.
If the diesel or additive didn’t fix your problem, you might need to replace the piston rings. To replace the piston rings, you need to remove the engine block’s pistons, which is a big repair.
You can do a leak-down test to make sure the piston rings or pistons are causing the problems.
#4. Replace Pistons.
You may also want to scrutinize the pistons while you replace the piston rings. If you see any damage to the pistons, you may need to replace them as well. When you replace the pistons, you often want to resurface the engine block.
#5. Replace Engine Block or Remanufacture Cylinders.
If your cylinder walls have scratches and are worn, you may need to resurface them or bore bigger cylinders with bigger pistons. The other option is to replace the engine block instead.
How to Prevent Blow-By From Harming Your Engine?
When it comes to blow by, an ounce of prevention is worth a pound of cure. As serious as the problem is, it can be easily prevented from occurring. Three of the best ways to prevent engine blow by are:
- Regular Maintenance: Lack of maintenance is one of the top reasons behind engine blow up. To prevent it from happening in the first place, you need to carry out regular engine maintenance. It is the key to reducing the chances of engine blow-by.
- Check for Solid Carbon Buildup: Carry out frequent checks for solid carbon buildup. Once formed, it will erode metal and damage the engine over time. You can use certain treatments to break down these dangerous solids, which will then be easier to remove.
- Use of Premium Fluids: Although little expensive, top-tier oil will help you prevent solid carbon buildup and help keep the engine in great shape for longer. Frequently changing the engine’s oil will keep the engine running longer and ensure combustion occurs correctly. You should routinely collect oil samples and have them inspected for any foreign particles and residue.
FAQs.
Q: What are the potential consequences of ignoring diesel blowby?
If ignored, blowby can damage multiple engine components, resulting in such a costly fix that your diesel technician might recommend a new engine altogether. In extreme cases, blowby can cause a runaway engine.
Runaway occurs when the fuel-oil mixture in the crankcase travels back to the combustion chamber. The mixture burns and causes the RPMs to exceed standard ratings, resulting in mechanical failure.
Q: Are there any aftermarket treatments available to reduce diesel blowby in diesel engines?
An air oil separator can help reduce diesel blowby. It works by catching and separating motor oil from blowby gases before being recirculated into the intake system.
Q: Can diesel blowby be prevented or minimized?
All diesel engines experience some level of blowby. Normal measurements are 1.5 cubic feet per minute (CFM) when the engine is hot to 3 CFM when the engine is cold.
Prevent blowby from exceeding these levels through routine maintenance, high-quality fuel and manufacturer-specified motor oil.
Conclusion
Blow-by is one of the common issues that face your engine, among other engine problems. They generally reduce the performance of your engine.
You may try accelerating, but due to engine blow-by, it may not peak as before. Usually, you have to sort the issue out before it is too late.
In the long run, you may have to find a way to prevent a blow-by from occurring because prevention is always better than cure. Hopefully, this guide has been great at imparting knowledge about blow-by.