What Is Engine Blow-by? What Does it Mean?

What Is Engine Blow-By? What Does It Mean?

Engine blow-by can affect all diesel engines, including the ones in your commercial generators. Knowing the signs and symptoms of blow-by can help you avoid this issue in the future.

What Is Blow-By on a Diesel Engine?

Engine blow-by is when a mixture of air-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.

You’ve probably seen or heard blow-by on the road as you’ve gone past a car or bus that has these signs. The same issues that happen to those cars or buses can happen with your generator engine.

How Much Blow-By Is Normal?

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.

Excessive blow-by is a sign of larger issues you’ll need to address before resuming operations.

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What Are Some Causes of Blow-By?

Blow-by happens when the internal combustion that occurs in your engine’s combustion chamber 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.

Additionally, any soot and deposits left over from incomplete combustion will collect on the rings, interfere with their seal and can further worsen engine blow-by.

Blow-by can also be caused by:

  • Bad, broken or improperly fitting piston rings
  • Piston damages or defects
  • Gaps or spaces between the piston rings

All of these issues create space where air and fluids from the engine can reach the crankcase and decrease engine compression.

How to Check for Blow-By

Your generator’s engine can give several signs of blow-by that you should be on the lookout for. Some engine blow-by symptoms include:

  • Noises: Loud or sputtering noises coming from the engine, possibly accompanied by exhaust clouds or vented fumes, are signs of blow-by.
  • White smoke: One of the most obvious signs of excessive blow-by is white smoke coming from the oil-fill tube or a valve cover.
  • Oil film: Another telltale sign is a layer of oil film around the tube, as blow-by causes unburned fuel to contaminate the oil and leak into the crankcase.
  • Increased oil and fuel consumption: If you’re noticing your generator is using more oil or fuel than normal, this could be a sign that much of it is leaking into the crankcase and causing blow-by.
  • Soot buildup: Blow-by contributes to increased incomplete combustion, which produces soot that’s retained within the cylinder walls.
  • Rough idling or misfiring: If your generator is difficult to start or keep running, blow-by might be the culprit, as blow-by affects important engine processes.

how to check for blow by

How Does Blow-By Affect Engines?

Blow-by inhibits overall engine performance due to a loss of compression. Diesel engines operate by compression ignition. They convert fuel to energy by pressurizing the cylinder, which creates heat and ignites diesel fuel.

When the cylinder has leaks, it can’t contain as much pressure, leading to misfiring and poor engine performance. Additionally, when gases expand and slip past the piston rings, they cannot effectively push the piston down to make the engine produce sufficient output during the power stroke, resulting in a drop in horsepower.

Blow-by also coats parts of the intake with oil and fuel. After wear and degradation of piston rings and cylinder walls, more air, fuel and moisture can slip into the crankcase and damage the parts.

Engines experiencing blow-by will also produce a much louder noise than normal and force polluting exhaust fumes out of the engine vents.

Blow-by will also result in increased fuel consumption. If components such as air, fuel and moisture slip into the crankcase, they can contaminate and dilute the oil. If there are any remnants of gases, unburned fuel, moisture, sulfur dioxide or soot particulates left behind in your engine’s compression chamber, these contaminants may slip into the crankcase. From there, they can seep into the engine and cause extensive damage.

Simply stated, engine blow-by can decrease your engine’s overall efficiency & performance, result in costly and time-intensive repairs or cause irreparable damage.

How to Prevent Blow-By

Whether you’ve already discovered blow-by in your diesel generator engine or are looking to avoid this issue altogether, engines without blow-by are crucial for the continued success of your business. Preventing blow-by is maybe easier than repairing the issues it causes and can save you time and money in the long run.

Some of the best ways to prevent blow-by include:

Preventative Maintenance

Proper engine maintenance is key to reducing the chances of engine blow-by. Frequently changing the engine’s oil will help remove any solid carbon buildup, which is known to erode metals. Adding treatments and detergents to the fuel and oil will help dissolve solids and buildup into liquid form so they’re easier to remove.

High-Quality Fluids

Using high-quality oils and fuels will also keep the engine running longer and will ensure combustion occurs correctly. Proper engine fluids will prevent the creation of solid byproducts like hydrocarbon combustion solids, which wear away metal.

In addition, you should regularly collect and send oil samples to a professional to have the oil checked for any foreign particulates and residue. Oil analysis can help inform you of any degradation occurring within the engine.

How to Fix Blow-By

If your engine is experiencing blow-by symptoms, major fixes may be necessary. Prioritize working on the affected engine, as blow-by issues can increase the longer they continue. A good first step would be to clean or replace piston rings, then clean or resurface the engine block cylinder walls. Alternatively, you may want to replace the engine or generator set altogether.

If you think your generator engine might be experiencing blow-by, or if you’re looking for a new, used, replacement or rental generator, please reach out to us at Woodstock Power Company!

The Woodstock Power Company Experience

Woodstock Power Company’s industry experts focus on commercial power generator sets, with in-depth knowledge to help you choose the right commercial or industrial generator for your needs.

Our experts are ready to assist you, from answering your questions about power generator sets to helping you find the best selection in our inventory based on:

  • Peak and average power requirements
  • Fuel preference for natural gas or diesel
  • Portability and stationary power
  • Prime and standby generator requirements
  • Available space and exhaust restrictions

Our experts can also help coach you on prime, continuous and standby power generators and teach you how to find the best surplus, new or used generator for your application.

We carry only the most top-rated power generator sets, providing you with generators that will fit your budget and give you great value.

Our generators have been thoroughly inspected, serviced and verified to ensure you’ll buy a quality machine you can rely on. We make all necessary repairs or modifications to our used generators to make them compliant with industry standards, and we fully test each generator before we sell it.

With our wide selection of generator sets, we’re confident you’ll find the model that best suits your operational needs.

We also buy used generators in good condition, so if you’ve already upgraded and are looking to sell your older model, get in touch with our sales team!

Feel free to contact us with any questions, concerns or inquiries to learn more about the Woodstock Power Company experience and the quality products and services we provide.

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