What Causes Fuel Dilution In Diesel Engines?

A customer recently contacted me to inquire about our Castrol Labcheck used oil analysis program’s fuel dilution alerting limitations.

After a brief conversation with the customer to learn why he was inquiring, he revealed that he had recently purchased a new vocational vehicle that was still under warranty. His problem was that the dealership where he acquired the truck and his Labcheck used oil analysis reports gave him contradictory information.

This truck, it turns out, has an issue with diesel fuel dilution of the engine oil. The results of Labcheck used oil samples consistently show high levels of fuel dilution, but when this customer contacted his dealership, he was told that the truck manufacturer allows up to 6% fuel dilution, so the dealership service department refused to provide warranty coverage for repairing the problem.

After doing some research, I discovered that this particular dealership was in violation of current OEM rules, which places a stricter limit on fuel dilution… up to 4% in some cases. Engine OEMs and customers can set various fuel dilution alarm limits if they want, but the Labcheck program has set limitations to offer the essential warning about potentially dangerous circumstances that might lead to increased engine wear or even catastrophic failure if not addressed.

Let’s look at why fuel dilution is such a risky situation. Internal leakage of the fuel injection system causes diesel fuel dilution of the engine oil. The causes vary by engine, however they can include sealing ring failure, loose connections, defective fuel injectors, or even extended durations of idling. The concern is, regardless of how the fuel enters the engine oil, at what level is it sufficient to destroy the engine?

The first is a fall in viscosity, the second is a dilution of the oil’s additive content, and the third is the introduction of a contaminant into the oil.

First, let’s look at viscosity. The most significant property of a lubricant, according to experts, is viscosity. The viscosity of the lubricant must be appropriate for the speed and load exerted on the moving parts inside the engine in order for it to lift and separate two moving bodies and keep them from colliding.

Any specific engine has a viscosity range that will work properly, and viscosities below or over that range can cause issues. To explain why, I’ll use the term “hydrodynamic lubrication” from the industry. This is the action of lubricating oil in the lubrication regime between two moving bodies, where it generates a “wedge” of oil that elevates and separates the parts. The oil will not produce this hydrodynamic wedge if the viscosity is either too low or too high.

This is a crucial part of lubrication and the foundation of wear prevention. As previously stated, introducing diesel fuel into the oil reduces the viscosity of the oil. When the viscosity falls too low or the load is too high, contact between the parts occurs, resulting in wear. Long-term fuel dilution can cause early engine bearing failure as well as aggressive wear of high-pressure locations like the valve train and piston rings / cylinder walls. Although long-term damage is a major worry, catastrophic failure can occur in a short amount of time if the fuel dilution is severe enough.

Wear is caused by a combination of factors, including lower viscosity and dilution of additive concentration in the oil. Special chemicals are included in engine oils to help prevent wear. These “anti-wear” additives are surface active, which means they have a natural affinity for the engine’s interior surfaces. They serve as a sacrificial layer of protection, and when the oil’s film strength is insufficient to keep the moving parts separated, the layer of anti-wear additives acts as a cushion.

Instead of “metal-on-metal” contact, “additive-on-additive” contact occurs. This protects the metal from wear, but it also wears away some of the added layer as it sacrifices itself to safeguard the engine components. The concentration of these anti-wear chemicals is diluted as fuel dilution of the oil grows, as does their capacity to prevent wear.

As if that wasn’t awful enough, there’s more bad news in the form of the injection of a foreign substance into the oil. Increased oxidation of the engine oil can occur as a result of fuel dilution. Oxidation is a natural aging process that occurs in all lubricants and is the primary limiting factor in the life of lubricating oil.

As the oil oxidizes, the color darkens, the viscosity rises, and corrosive chemicals form, which can harm the engine’s internal components, particularly the delicate metals utilized in the engine bearings. Oxidation can lead to the production of sludge and varnish deposits in addition to corrosion.

Now we must consider the technology available to aid in the detection of levels of fuel dilution in oil. Regrettably, this is not a simple procedure. To begin with, we’re discussing one hydrocarbon (diesel fuel) within another hydrocarbon (oil) (engine oil). The majority of molecules in diesel fuel and lubricating oil are made up of carbon atoms bonded to hydrogen atoms. The size of the molecules, or the number of carbon atoms in each, is the fundamental difference between diesel fuel and motor oil.

So, how do we know how much of one is in a homogeneous mixture of the two once they’ve been blended together? Different laboratories employ various technologies with varying degrees of accuracy. Each method, from a basic open-cup flash test to Fourier Transform Infrared Spectroscopy to Gas Chromatography, has its own set of strengths and disadvantages, as well as its own level of accuracy. A single sample of used oil with a specified percentage of fuel dilution can yield a broad range of test results depending on the method employed and the skill of the test operator.

The true issue of gasoline evaporation makes things considerably more difficult. The volatility of diesel fuel is substantially higher than that of engine oil. This implies that as the engine warms up and the engine oil is exposed to the high temperatures of a running engine, part of the fuel in the oil will evaporate. As a result, actual fuel dilution in oil is often larger than what is measured and indicated in a used oil analysis report.

Engine manufacturers will tell you that a specific amount of gasoline dilution is allowed, but do they know which lab test method was utilized and how much fuel evaporation has occurred? Without that information, how can a random number or percent of dilution be assigned? What are the responsibilities of a fleet or heavy equipment owner/operator?

Castrol has two viewpoints on this situation: as a lubricant supplier and as a lab services provider. In both cases, fuel in the oil is a bad thing. We understand the problems that fuel dilution poses to our clients because oil is not designed with gasoline as an intended component.

As a result, we’ve set fuel dilution limitations in Labcheck that we believe are suitable based on real-world data. It is, nevertheless, acceptable to define custom restrictions. If you find yourself in this circumstance, we hope that this essay will assist you in making a more educated decision.

Please keep in mind that Castrol’s team of knowledgeable field engineers is available to assist you with fuel dilution concerns or any other queries you may have about your used oil analysis or fleet maintenance programs.

How do you fix fuel dilutions?

Checking the fuel injector nozzles, in addition to regular oil checks and changes, can help to reduce the occurrence of fuel dilution—as dirty nozzles can prevent the fuel from atomizing correctly, and thus prevent the fuel from combusting efficiently—so failing to keep up with maintenance in this area is another way of causing fuel dilution.

What causes oil dilution in diesel engines?

Unburned diesel or gasoline accumulates in the crankcase of internal combustion engines, causing crankcase dilution. Excessively rich fuel mixtures or incomplete combustion allow a little quantity of fuel to enter between the pistons and cylinder walls, causing the engine oil to become diluted. In cases when fuel is injected at a very high pressure, such as in a direct-injection diesel engine, it is more common.

It is totally conceivable for fuel to condense on the cooler regions of an engine’s cylinders when a mixture of air and fuel enters the cylinder. The condensate could wash the lubricating oil off the cylinder walls, pass through the piston rings, and accumulate in the oil pan, increasing wear and diluting the lubricating oil. Because the less volatile fuel components have the highest tendency to condense, the degree of crankcase-oil dilution is proportional to the mixture’s end volatility temperatures.

How can fuel dilution be reduced?

Fuel dilution can be caused by a variety of factors, including driving conditions. There isn’t much you can do in this situation except, if possible, adjust your driving style.

  • Longer journeys should be incorporated to guarantee that the engine reaches operational temperature for several minutes.

To avoid increased wear, use a high-quality synthetic motor oil if gasoline dilution is an issue. (In any case, you should do it.) Although oil film thickness is proportional to viscosity – and excessive fuel dilution affects viscosity independent of oil quality — film strength is determined by the quality of the base oil and additives. To help preserve components from wear, AMSOIL synthetic motor oils contain high-quality base oils and additives.

Finally, follow the manufacturer’s instructions for oil changes. Severe-service vehicles are prone to gasoline dilution, therefore follow the severe-service requirements in your owner’s handbook or on the motor oil label.

What typically causes oil dilution?

One of the most common causes of oil dilution is the migration of refrigerant into a broken refrigeration system.

The refrigerant vapors move to the circuit’s lower pressure section (the coolest) and condense there. This migration process continues until the refrigerant’s pressure-to-temperature ratio is uniform throughout the system.

The affinity between oil and coolant aids migration as well. The compressor, as a massive mass of cast iron, is often the coldest portion of the refrigeration system after many hours of downtime. The refrigerant vapors condense in a certain way at the engine-compressor compartment level. Furthermore, because the oils often utilized have an affinity for the refrigerant, dilution occurs quickly if the affinity between oil and refrigerant cannot be reduced.

Most compressors have resistors on the cup to reduce this diluting effect; these resistors are meant to maintain an oil temperature of 10-20 ° C higher than room temperature; this temperature increase reduces the miscibility of the oil with the refrigerant.

The oil cup’s resistance does not keep the oil from being diluted by the refrigerant as it migrates to other parts of the refrigeration system, nor does it help to evaporate huge amounts of refrigerant that have already been diluted in the compressor.

Installing an occasional “pump down” system is a valid technique to tackle migration concerns.

What problems does oil dilution cause?

Oil dilution is another impact of fuel spilling into the crankcase. This reduces the viscosity of the lubricant, making the films formed weaker and less capable of withstanding strong stresses that can occur at certain places, such as the rod bearings and crankshaft.

What happens if the viscosity isn’t high enough? As a result of the contact between the metal surfaces, the bearings wear out quickly owing to friction.

Biofuel is a third impact of fuel going through the crankcase. Biofuels are currently included in the formulas for both diesel and gasoline (biodiesel in the first case, and bioethanol in the second).

Because the fuel is exposed to high temperatures in the crankcase, some of it evaporates, resulting in a concentration of biofuel in the case of diesel fuel. As a result, the biodiesel is less fluid and viscous than diesel fuel, causing the lubricant to thicken.

For example, with a diesel fuel containing 7% biodiesel, the diesel component evaporates in the crankcase, resulting in a biofuel concentration of more than 10% biodiesel. The viscosity of the lubricant and fuel mixture increases as a result of this impact, and bearing wear can accelerate dramatically.

How do you test for fuel dilution?

Fuel dilution can be measured using a variety of methods. Viscosity analysis is an important screening technique that is commonly used to assess the lubricants in use. Direct procedures for testing fuel dilution include gas chromatography, flash point testing, and surface acoustic wave detection.

What happens when too much oil is injected in the working cylinder?

For many years, there has been a widespread belief that the more oil used to lubricate cylinders, the better. Overlubrication of a two-stroke engine can be detrimental to the cylinder condition, resulting in excessive cylinder liner and piston ring wear, as well as piston ring breakage or jamming.

Can I put oil in my diesel fuel?

Instead, use a diesel fuel additive like AMSOIL Diesel All-In-One or AMSOIL Diesel Injector Clean to maintain the combustion chamber clean and lubricate the fuel system.

When compared to metering out a few tablespoons of 2-stroke oil and finagling it into the fuel tank without making a mess, they function better and are significantly easier to use.

They also provide a number of other advantages that help keep your diesel operating smoothly, such as…