What Causes Engine Blowing-by? Common Causes and How To Fix Them

Are you concerned that your engine is blowing by too often?

It is a pity! Blowing-by repairs can be very costly and lead to expensive repair work.

What is blow-by, and how can it be caused? Let’s find out!

Engine Blow-By: What does it mean?

The engine blow-by refers to the compressed air and fuel from the cylinder combustion chamber passing through the piston rings into crankcase ventilation. This is usually caused by worn piston rings or worn pistons.

An internal combustion engine operates by the ignition of gas and air. A blow-by happens when the explosion reaches the crankcase via the piston rings, and out the engine.

You may notice loss in horsepower if the pistons leak and cause blow-by. If left untreated, blow-by can lead to engine damage and increased oil consumption.

There are 4 common causes of blow-by

Worn piston rings, damaged pistons and damaged cylinder walls are all common reasons for blow-by. 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.

A few things can cause blow-by. Blow-by can often be a serious problem that is difficult to correct.

However, if you experience blow-by, you will want to check the crankcase breathing to make sure it’s not blocked first.

Below is a list that explains the four most frequent causes of engine failure.

1. Pistons that are worn out

The crankshaft is moved by the pistons. As the pistons wear down, the walls of the cylinders get smaller. 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.

Soon, the fuel-air mixture finds its way to the crankcase. You may also experience this problem with a knocking motor's pistons.

2. Worn piston rings

As the piston rings move in the cylinder walls, they wear out and are destroyed over time. It can lead to gas leakage, which may cause blow-by.

The piston rings may sometimes get stuck. To solve this, you can pour some diesel in the cylinder and allow it to sit for awhile. They will eventually come free and be sealed against the cylinder wall once again with a bit of luck.

They can also be replaced. This is very expensive.

3. Cylinder walls damaged

Constant movement of the pistons could cause damage or cracking to the cylinder walls. Damaged piston rings or piston pistons can cause it.

Listening for the piston slap can help you identify damaged cylinder walls. It is rare to find a deteriorated cylinder wall. It is possible to either bore out the cylinders and change the pistons or replace the engine block.

4. Ventilation from the crankcase is faulty

Sometimes, blocked crankcase ventilation can be mistaken for blow-by. This is because the crankcase ventilation works to recycle any blow-by back into your intake. You may believe that there is too much blow-by if the crankcase ventilation pipes are blocked.

Make sure to inspect the crankcase ventilation.

What can you do to fix a 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.

Blowing by is not always easy, especially if it's not your lucky day. Wearing piston rings or piston pistons are what most often cause it. There are some steps you can take to correct it.

1. Ventilation for Clean Crankcase

Check your crankcase ventilation for sludge or dirt. Try to remove a hose and blow through it to make sure it’s clear. Check the valve's PCV.

2. Oil Treatment

It happens sometimes that piston rings become stuck, and they will not fit against the cylinder walls. You can solve this problem if you're lucky by pouring diesel into your cylinders. Let them rest for several days. This can be done with special additives:

3. Piston rings can be replaced

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. A leak-down test can be done to determine whether the piston rings are the cause of the problem.

4. Replace Pistons

It is also a good idea to inspect the pistons before you change the rings. You may also need to replace the pistons if you find any damage. Resurfacing the engine block is a must when replacing a piston.

5. Repair or replace the Engine Block

Your cylinder walls may be worn or scratched. You can either repair them, bore bigger cylinders and use larger pistons. You can also replace your engine block.