Engine Blow-by: What is it and How to Fix it

All diesel engines, including those in your business generators, are susceptible to engine blow-by. Internal combustion engines are essentially controlled bombs that burn fuel and air to drive crankshafts and pistons. Although there are other byproducts of violence, power is one of them.

Increased piston pressure drives droplets of gasoline, oil, and combustion gases into the crankcase via the piston rings during the combustion process. This mixture is known as engine blow-by. A blown engine is one of the most expensive repairs that owners frequently face.Engine Blow-by: What is it and How to Fix it

Furthermore, the vehicle’s performance suffers and its oil consumption rises. Well, in this article, we’ll get to discuss the engine blow-by. That said, the answers to the following questions will be addressed:

  • What is an engine blow-by?
  • Why does blow-by occur in a car engine?
  • What are the symptoms of engine blowout?
  • How do you fix an engine blow-by?

So let’s get started!


What is an engine blow-by?

When the air and fuel in the cylinder combustion chamber pass through the piston rings and enter the crankcase ventilation, it is known as an engine blow-by. This issue is often caused by worn piston rings, worn pistons, or a damaged cylinder wall. Internal combustion engines function by igniting air and fuel. A blow-by occurs when this explosion travels to the crankcase via the piston rings and subsequently out of the engine.

You may notice a reduction of horsepower if the pistons are leaking and producing the blow-by. If not addressed, blow-by will cause more engine problems as well as increased engine oil usage. Pistons are essential for crankshaft movement. When the pistons wear out, they become smaller, while the cylinder walls grow larger.

Why does blow-by occur in a car engine?

Pistons are generally constructed of aluminum, which is a soft metal. When it wears out, it creates grooves in the piston and deposits on the cylinder walls. The fuel-air mixture quickly enters the crankcase. It could also be attributed to holes in the pistons caused by a knocking engine.

The piston rings are constantly pushed back and forth in the cylinder wall, and they wear out and are damaged over time. This generates gas leakage, which causes a blow-by. When the piston rings become stuck, it is often necessary to pour some diesel into the cylinder and let it sit for a bit. With luck, they will come loose and seal against the cylinder wall once more.

If not, the only option is to replace them, which is an extremely expensive fix. The constant movement of the pistons will eventually destroy the cylinder walls. It can also result from damaged pistons or piston rings. Listening for piston slap can typically reveal damaged cylinder walls.

Fortunately, worn-out cylinder walls are uncommon. If this occurs, you must either bore the cylinders to a larger size and replace the pistons, or you must replace the engine block. In some circumstances, you may misinterpret limited crankcase ventilation for blow-by.

The job of crankcase ventilation is to recycle blow-by back into the intake. If the crankcase ventilation hoses are clogged, when you open the oil cap, it will push it out, giving the impression that your engine has a lot of blow-by. Make sure the crankcase ventilation is clean and free of debris.

What are the symptoms of an engine blow-by?

Here are the most common symptoms of an engine blow-by:

  • Blue Smoke from Exhaust
  • White Exhaust Fumes
  • Engine Rattling or Knocking
  • Engine Oil Coolant
  • Failure of the Engine

Blue Smoke from Exhaust

A blue cloud of smoke coming from your vehicle’s exhaust pipe could indicate that the engine has blown up. This sign indicates that some raw engine oil is being spilled into the chamber where combustion occurs.

Engine Oil Coolant

The engine’s cooling systems and engine oil are always maintained sealed and in separate compartments. If you discover engine oil in the coolant or coolant in the engine oil, this could signify a fatal internal condition that must be addressed immediately.

Engine Rattling or Knocking

If you hear internal engine noises while the engine is running, this is a red flag that something has gone horribly wrong. Broken parts or worn-out bearings are common causes. In most circumstances, there is little chance of a knocking engine.

White Exhaust Fumes

Another sign of a blow-by is the release of white gases from your vehicle’s tailpipe. White emissions indicate that water or engine coolant is possibly entering the combustion chamber. This exhaust fume is often dense and, unlike other fumes, hangs in the air.

Failure of the Engine

A variety of factors might cause an engine to fail to start. A blown engine is one of these reasons. If this is the case, an engine blow-by repair is required to get your car back up and running.

How do you fix an engine blow-by?

If you’re experiencing engine blow-by, you can try one or more of the following to resolve the issue:

Ensure a Clean Crankcase Ventilation

The first step is to ensure that your crankcase ventilation system is free of sludge and grime. Remove a hose and blow through it to ensure that it is clear. Check the PCV valve as well.

Oil Treatment

Sometimes the piston rings become jammed and will not seal against the cylinder walls. If you’re lucky, pouring some diesel into the cylinders and letting them sit for a day or two will remedy the problem.

Replace the engine block or remanufacture the cylinders

If your cylinder walls have scratches and wear, you may need to resurface them or bore larger cylinders with larger pistons. The alternative is to replace the engine block.

Replace Piston Rings

If the diesel or additive does not solve your problem, you may need to replace the piston rings. To replace the piston rings, you must first remove the pistons from the engine block, which is a major repair. You can do a leak-down test to ensure that the piston rings or pistons are the source of the problem.

Replace Pistons

You should also inspect the pistons while replacing the piston rings. If you see any damage to the pistons, you may need to repair them as well. When replacing pistons, it is common practice to resurface the engine block.

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What causes a blow-by in a car engine?

The majority of blowby occurs when exhaust gas enters the crankcase via the piston rings, but additional causes include turbochargers. Blowby introduces pressure and combustion gases into the oil pan as it passes through the piston rings.

Is blow-by bad for your engine?

However, blow-by can coat your intake with oil and/or gasoline over time, drastically lowering engine efficiency. Worse, under the right conditions, blow-by can condense inside the crankcase and enter your engine’s head and cylinders. This can reduce the octane rating of your gasoline.

What are the signs of blow-by?

Loud or sputtering engine noises, possibly accompanied by exhaust clouds or released fumes, are indicators of blow-by. White smoke: White smoke emerging from the oil-fill tube or a valve cover is one of the most visible symptoms of excessive blow-by.

Can too much oil cause blow-by?

Overfilling the crankcase by half a quart or so is insufficient to cause this issue. Excessive blow-by on older engines can be caused by piston rings that are all worn down and allow too much material to pass through them. And that is a much more serious, and costly, issue.

What is the best oil treatment for Blowby?

The following two steps can help to reduce engine blowby: Step 1: Mix FTC Decarbonizer into the diesel. Step 2: When doing an oil change, use Flushing Oil Concentrate. To reduce engine blow-by, FTC Decarbonizer is added to the diesel at each fill, and you essentially just drive the engine clean!

Will thicker oil help blow-by?

In the near term, using thicker oil or oil additives to seal the ring can help. However, this will have minimal effect on reducing friction heat. When heated, oils degrade quickly. So using a heavier oil only masks the problem for a short time.

Can blow-by cause oil leaks?

If the engine produces more blow-by gases than the PCV system can handle, a rising surplus accumulates in the crankcase, causing excess pressure and, inevitably, oil leaks. When confronted with increased internal crankcase pressure, even the most perfectly sealed gaskets leak.

And that is all for this article, in which we looked at engine blow-by. Nevertheless, the answers to the following questions have been discussed:

  • What is an engine blow-by?
  • Why does blow-by occur in a car engine?
  • What are the symptoms of an engine blow-by?
  • How do you fix an engine blow-by?

Hope you learn a lot from the reading. If you do, kindly share it with others. Thank you for reading; see you around!


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