How to Prevent and Fix Engine Blowby

How to Prevent and Fix Engine Blowby
April 8, 2021

Diesel engines contain different internal metals that expand and contract at varying rates. While these metals are necessary for operation, gaps between various parts can lead to poor sealing and another common challenge — excessive blowby.

Read our guide or view our products to find solutions for your problems.

What Is Blowby on a Diesel Engine?

Every engine has some level of blowby, but what is blowby? Blowby is the leakage of any combustion gases or pressure into the engine’s crankcase. Most blowby occurs when exhaust gas enters the crankcase by going past the piston rings, while other sources include turbochargers. 

Blowby that passes the piston rings introduces pressure and combustion gases into the oil pan. These gases may contain fuel that hasn’t burnt properly or particulates, resulting in condensation due to temperature differences between the crankcase and the combustion gas. When engine oil combines with blowby, they create acids and sludge that can cause harm to other engine parts. Unspent fuel also dilutes your oil’s viscosity and lubricity, which can adversely impact your valve train, cylinder walls and engine bearings.

What Are the Causes of Diesel Engine Blowby?

Blowby has several causes, including:

  • Misplaced or worn out rings: Some rings break down, stick to cylinder walls, become loose through engine vibration no longer have a good seal.
  • Eroding cylinders or pistons: High mileage, constant wear and a lack of routine upkeep can cause misalignments and create gaps for engine blowby.
  • High carbon levels: Build-up is common in the piston ring’s grooves and older diesel engines without electronic fuel injectors.

Issues Blowby Can Cause

Engine blowby can cause a plethora of problems. One of the most common is cracking piston rings and ruining HEUI fuel injectors in early Powerstroke engines. Ignoring this problem could not only cost your fuel injectors, but also it more than likely will foul your turbo, EGR Valves, and DPF. These are not cheap fixes either — you’re looking at being out thousands of dollars and potentially dealing with the same problems in a few years. 

Overall you will notice a loss in engine performance and fuel economy. Air, fuel, and other contaminants will slip into the crankcase and cause all types of problems. This is because engine blowby causes gaps and cracks in the piston rings, and by that time it’s often too late, you’ll be forced to replace piston rings, an expensive repair! 

How to Identify and Test for Blowby in Your Diesel Engine

How do you know if you have excessive blowby?

One of the tell-tale signs of excessive blowby is white smoke billowing from the block oil-fill or opening on a valve cover. To check this, set the oil-filler cap upside down on the tube or opening. If it immediately blows off, there definitely is too much crankcase pressure. 

Checking the engine’s compression by performing a leak-down test is a more detailed method of diagnosing the condition and determining the amount (percentage) of blowby. The test is completed using a compressor and the specialized dual-gauge testing tool. 

While the leak-down test tells you how much pressure your engine holds, the crank compression test sees how much force it can generate. Cranking compression builds up in the cylinders when the piston moves up to compress and the valves are closed. Measure this in pounds-per-square-inch (PSI) with a compression testing gauge and monitor inconsistent results across the cylinders.

You can also measure the output from your crankcase with a blowby flow meter. Attach the tool to your crankcase vent and run your engine to force air through the meter. Compare this airflow measurement to what’s considered normal blowby for your engine — divide your engine’s maximum horsepower by 50 to get an approximate number.

How Do You Fix Blowby?

For the right fix, you need to know the cause. Some steps to take include:

  • Check your positive crankcase ventilation (PCV) valve. These valves can stick in the open position, permitting the oil to sneak past the gaskets and dirt to build up. Signs that your PCV valve may be the cause include surging, black smoke and engine sludge.
  • Consider an additive. Blowby can sometimes result from inadequate lubrication. You can improve performance and prevent rings from sticking with Hot Shot Secret’s Diesel Extreme fuel additive and the FR3 oil friction reducer.

Piston from engine

How Do You Prevent Blowby?

So is there anything you can do to prevent this from happening to your beloved truck? Actually yes, there is. 

It starts with using a high-quality oil, like Hot Shot’s Secret Blue Diamond Engine Oil. By using a high-quality oil you ensure your engine is running smoothly and reducing the friction that can cause engine blowby (caused by stiction). So using high-quality oil is step 1, step 2 is actually cleaning out what causes engine blowby, stiction. 

We recommend adding Hot Shot’s Secret Stiction Eliminator every 3rd oil change to make sure your engine is free of stiction. Hot Shot’s Stiction Eliminator was specifically designed to safely clean your engine of stiction. By cleaning the stiction, the rings will move more freely, allowing for a tighter seal between the cylinder walls and the piston. That way you can avoid devastating engine blowby and the expensive manual cleaning of your pistons or even piston replacements.

No one wants to experience engine blowby and not one soul wants to have to pay for the damages engine blowby brings with it. The old saying “you get out what you put in” holds true for your diesel engine. It always pays off in the end to take care of your engine upfront by using quality fluids and adding a little bit here and there to keep things clean and running smoothly.

Use Hot Shot’s Secret to Prevent Blowby on Your Diesel Engine

Keep your diesel engine in its best running condition with our complete line of engine fluids. At Hot Shot’s Secret, we use experience and science to bring you the best products to improve your vehicle’s performance. In addition to our Blue Diamond Engine Oil and Stiction Eliminator oil additive, you’ll find a complete line of other diesel fuel additives and specially formulated transmission fluids, all backed by our 100% satisfaction guarantee. 

Shop our products online or contact a representative for expert assistance.