How To Check Blow By In Diesel Engine?

Rough idling and misfiring, for starters, can signal a problem. White smoke pouring from the oil-fill tube or a valve cover opening is one of the telltale indications of severe blow-by. Turn the oil-filler cap upside down on the tube or opening to see if this is the case. If it blows off right away, there is clearly too much crankcase pressure. Residual oil layer around the tube is another clear identifier—it comes before the smoke, in fact. Blow-by also results in polluted, diluted oil in the engine’s crankcase (due to unburned gasoline). When there is a lot of blow-by, the mixture might cause a diesel to run away if it gets into the combustion chamber.

How do you measure Blowby on a diesel engine?

Contrary to popular belief, an engine has more blowby at idle than at higher rpms, according to one blowby flow meter manufacturer. The rings actually seal better as the speed increases, and blowby decreases.

What is the normal amount of blowby? By multiplying an engine’s maximum horsepower output by 50, you can get a rough estimate of how much blowby to expect. With normal piston rings and ring end gap tolerances, a street performance engine with roughly 500 horsepower will typically have about 10 cfm of blowby. Higher-performance engines with tighter tolerances, as well as those with gapless piston rings, are likely to have less blowby. For example, a NASCAR motor with 800 to 900 horsepower might only have 5 cfm of blowby.

How do I know if my engine has Blowby?

When air-fuel mixture or combustion gases seep between a piston and the cylinder wall into the crankcase of an automobile, this is known as engine blow-by.

Engine blow-by can be identified by loud or sputtering noises coming from the engine, which may be followed by clouds of exhaust or expelled fumes. When you’re driving or walking down the sidewalk and encounter a car or bus with these placards, you’ve undoubtedly seen or heard it. The same principle that is at work in a car or a bus is also at work in your generator engine.

So, how does this take place? It occurs when pollutants such as air, fuel, and moisture are driven past the piston rings within the crankcase during internal combustion in your engine’s combustion chamber. If your engine’s piston rings aren’t well-fitting, they won’t be able to retain the pressure created by combustion, resulting in air-fuel mixture leakage and impurities.

It should be mentioned that engine blow-by is not limited to diesel engines; it can also occur in gasoline engines.

What causes blow-by in a diesel engine?

On a diesel engine, you may need to check for any of the following signs in your cylinders to quickly repair or eliminate the problem:

  • Piston rings that are badly worn out or broken – This can happen if dirt and filth become lodged inside the pistons and the pistons grind away at them over time. Because it is impossible to fit new piston rings around old ring lands, you will need new piston rings to address this problem (the edges where the piston rests).
  • Oil weeping onto cylinder walls – This occurs when oil accumulates around the pistons instead of being equally spread throughout the cylinder wall, lubricating every portion of it. On a diesel engine, the oil will collect in little pools and leak over the walls, causing blow-by.
  • Carbon build-up — If you have an older automobile with mechanical injection systems rather than electronic ones, this might result in increased carbon build-up inside the cylinders, which can lead to issues like blow-by.

If your diesel engine’s pistons show any of these indicators, it’s probably time for some maintenance or repairs!

What Causes a Blow By in a Diesel Engine? Blow-by can occur in a diesel engine if the piston rings are damaged or smashed. Due to the back-and-forth grinding, the piston’s sealing ability deteriorates with time, causing damage. The failure of the pistons allows gases to escape to the back of the ring, resulting in blow-by of the diesel engine.

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How can you lower Blowby?

The easiest technique to reduce crankcase vapor pressure – sometimes known as blow-by – is to seal the engine as tightly as possible from cylinder pressure. Customizing the end gaps on the top two rings to meet the engine’s intended function is one technique to lessen ring end gaps.

What is the normal blow by of a diesel engine?

“Blow-by” is a word that applies to all types of engines—diesel, gas, and so on. The gas leaks past the piston rings and into the crankcase when the pressure in the oil pan is higher than the pressure in the cylinder bore.

What causes Blowby in diesel engine engines?

Engine blow-by can be caused by a damaged or smashed piston ring. Due to the back-and-forth grinding, the piston’s sealing ability deteriorates with time, causing damage. The failure of the pistons allows gases to escape to the back of the ring, resulting in blow-by of the diesel engine.

How much Blowby is normal?

Furthermore, engine temperature and load are inextricably linked to blowby. A 12-liter engine in good mechanical condition can produce 1.5 cubic feet per minute (cfm) of blowby at idling at normal operating temperature, but 3.5 cfm when cold. The blowby at full load could be as high as 2.7 cfm.

The remaining 40% of blowby originates from sources that most people overlook, such as the turbocharger or the air brake compressor on a truck. When diagnosing an extreme blowby issue, look for any engine components that are connected to engine oil and, consequently, the crankcase.

The source of the blowby will dictate how it appears and what long-term consequences it may have. Blowby that passes through the piston rings not only pressurizes the oil pan, but also introduces unburned fuel, particulate matter, and nitrogen oxide emissions. Due to the temperature difference between the combustion gases and the crankcase, they also cause condensation.

Blowby produces sludge and acids when coupled with motor oil, which attack all engine parts. The unburned fuel dilutes the engine oil’s lubricity and viscosity, causing damage to engine bearings, valves, and cylinder walls.

When an engine brake is installed, higher-than-normal blowby is induced when the system is activated. The piston flutters and the rings flutter when evoked, causing them to loose their seal. The engine brake is intended to assist in stopping the car and reducing friction wear, however it should not be used in excess.

The oil from the piston and rings is torn away by Blowby. It vaporizes first, then turns into an aerosol, leaving a film or fumes around the crankcase vent tube.

One word sums up the key to reducing blowby: sealing. Between the piston rings and the cylinder wall, as well as other locations such as the turbocharger and, if necessary, a compressor, an effective seal must be developed and maintained. Blowby won’t be an issue if the combustion gases and pressure are kept where they should be.

The crankcase needs to breathe since every engine has some level of blowby. Because a turbocharged diesel engine cannot use a PCV valve, this is more difficult than with a normally aspirated gas engine. An open vent pipe may be present in a heavy-duty diesel, depending on its application and age. This is exactly what its name implies. Its job is to reduce crankcase pressure; it doesn’t do much to eliminate combustion gases or moisture. Separators may be used in newer engines, and this is referred regarded as a closed system. The engine oil is separated and the combustion gases are fed back into the induction system using this configuration. The oil is removed to avoid damaging the vanes on the turbocharger compressor wheel and fouling the intercooler’s heat exchange capacity. An oil separator and an open vent pipe may be seen on some engines.

How do you know if your diesel needs to be rebuilt?

There are a variety of reasons why you might need to rebuild your diesel engine. The following are some signs that you might have a problem that needs to be looked at.

Power Loss

Loss of power may suggest a problem with your camshaft, but it could also indicate a more serious problem with your engine. Fuel issues, particularly severe fuel contamination, excess buildup, injector issues, a defective turbo, or air entering the system can all cause this.

Poor Fuel Economy

If your camshaft is having problems, such as lobe wear, you may notice a drop in mileage. There’s a risk that bad driving behaviors, such as carrying too much weight or accelerating quickly, are causing a decline in fuel economy. It could also indicate that your diesel engine needs to be rebuilt. It’s possible that your gasoline is polluted, that you have a problem with your filter or injectors, or that you have a leak in your system.

Check out our 5 Simple Methods to Improve Fuel Economy if you’re seeking for ways to save money at the pump.

Excessive Oil Consumption

If your engine is using more oil than usual, you should identify the problem before it leads to a serious system breakdown. Dirty oil, too much oil in the crankcase, excessive engine vacuum, too little end clearance of piston rings, worn or damaged piston rings, oil pressure too high, lugging engine, or restricted air intake could all be contributing factors.

The piston rings become compressed in the ring groove as a result of carbon packing caused by malfunctioning EGR systems, and are no longer able to hold combustion gasses on the top side or manage the oil on the bottom side. If oil is burning or leaking, it can cause other problems and result in a more expensive repair if not addressed immediately.

We offer further information regarding high oil consumption if your rig is guzzling oil.


Engine banging can signify a major problem with your engine, therefore it’s important not to dismiss it. Compression issues, malfunctioning fuel injectors, timing issues, failing bearings, and a failed wrist pin bushing or wrist pin are all possible reasons of engine banging.

Compression Issues

A lack of compression is one of the most obvious signs that your engine has a problem that has to be addressed. Leaking/broken valves, leaking/broken piston rings, blown head gasket, camshaft troubles, broken timing belt, or a hole in the piston or cylinder are all signs of compression problems.


Excessive smoke coming from your exhaust, especially blue or black smoke, can indicate a major problem with your engine. This could suggest a variety of issues, including malfunctioning injectors, injector pumps, air filters, EGR, turbos, carbon build-up, inefficient or incomplete combustion, worn valve guides or seals, or wear in power assembly.

How do I know if my diesel engine is healthy?

Blue smoke isn’t a nice thing. Here is a link to a complete article detailing all of the potential issues. Your engine is burning oil in some way if you see blue smoke. This is not always due to worn components, but it is a common occurrence in older engines.

If you’ve determined that the issue isn’t with the gasoline system, it’s likely that an engine component is malfunctioning. As the engine ages, you’ll notice more and more blue smoke. Over time, the clearances on the cylinder walls simply cannot be maintained, and oil accumulates on the walls of the cylinder. When the piston returns to its original position, oil is left in the chamber, where it is burned together with the fuel.

Once again, a compression check will reveal the source of the problem. It’s possible that a complete in-frame rebuild is required if it’s quite old. That oil has been traveling through those rings for a long time, as you can see below.

How do I know if my diesel has low compression?

Low power and poor fuel economy are two signs of inadequate compression that are comparable to those of fuel contamination. You might also notice that your engine is running rougher than usual, that there is a lot of blow-by, or that your exhaust is emitting white smoke. If any of these symptoms occur in your engine, a compression test should be performed to determine whether low or no compression is the source of the problem. Depending on the afflicted components of the engine, compression difficulties can often necessitate an engine rebuild.

What is good compression on a diesel engine?

Compression levels in a diesel engine should be between 275 and 400 psi. A difference of more than 10% between cylinders is generally not desirable. You should be fine if you keep these two points in mind.

How do I remove Blowby?

“FTC Decarbonizer is added to the diesel at each fill to prevent engine blow by, and then you simply drive the engine clean! The decarbonization procedure is delicate and gradual, but effective, cleaning turbos and DPFs in the process.”

To restore full cleanliness to the lower piston rings, most engines will need to be cleaned from the oil side as well. This entails flushing the engine with Flushing Oil Concentrate. It targets hard, baked-on deposits and engine sludge with detergents and, according to the producers, restores the engine “throughout “as new clean”

The longer you ignore blow-by, the more carbon builds up in your engine. Black smoke and oil soot levels are rising! The vehicle’s performance and fuel economy decline. Excess carbon on pistons can lead to premature wear. Carbon buildup in the ring grooves causes the majority of fractured piston rings. The chance of engine failure is considerably lowered by cleaning the engine and, more importantly, keeping it clean!

Engine blow by reduced

The images below are from a decade ago, when Caterpillar D11R dozers were working in Queensland’s Bowen Basin. The rebuild life was estimated to be around 11,000 hours. Many failures occurred as a result of excessive carbon buildup, with some failures occurring after only 3000-4000 hours. Rebuild intervals were typically 8,000-10,000 hours. FTC Decarbonizer was used by one 10-piece fleet that stood out! At 15,000 hours, the first engine was pulled down and determined to be in great condition. They eventually settled on 18,000-hour rebuild intervals.

Turbochargers, EGR valves, and diesel particulate filters are all clogged by increased exhaust soot. Turbo seals are chewed away by increased oil soot. Blowby is responsible for a lot of disastrous failures.

Engine blow by difficulties can be resolved, resulting in engines that are less stressed, more efficient, and last longer. The key to extending the life of Euro V emission-controlled engines is to burn the fuel cleanly for low exhaust soot and low oil soot levels.