Facing Fuel Dilution: Spotting Problems Early

antique stored (1200x675)

The engine oil in vehicles stored for the winter months or longer periods should be checked for fuel dilution, particularly if the vehicle was periodically cranked but not driven down the road.

Words by Cindy Bullion

Did you follow the generations-old rule of cranking your stored vehicle monthly this past winter, or while it was put away for an even longer period? If so, you could be facing fuel dilution issues as you wake that vehicle from its hibernation. Yes, grandpa’s advice may have steered you right into a problem situation.

While fuel dilution — the result of engine oil mixing with unburnt fuel in the crankcase — is attributable to many causes, the effects are always reduced oil viscosity and, thus, performance. Unchecked, fuel dilution can eventually lead to damaged components and engine failure.

Certified Lubrication Specialist Lake Speed Jr. of Driven Racing Oil explains as little as a 5 percent fuel dilution can lower the viscosity of an SAE 30 grade oil to SAE 20, meaning there is less of an oil film to protect surfaces, the oil is also less stable in high temperatures, and its cleaning properties are compromised. Don’t change that oil sooner than planned and you’re bound to end up with wear, or worse.

He advises fuel dilution of 4 percent or greater warrants immediate action. But, how do you know if your engine oil falls into that category? Oil analysis.

“When you take your vehicle out of storage, it’s not a bad idea to pull a sample,” says Speed, adding you may also detect severe cases of fuel dilution by checking to see if the oil level rose on the dipstick during storage. “Fuel dilution problems can be spotted before the problem becomes severe.”

If you’re unsure about whether to spend the time and bucks — $22 through Driven (PN DR100-21) or around $30 if you pick up a kit from a heavy equipment dealership — on an oil analysis, only to find out there was no fuel dilution issue, Speed recommends using one of Driven’s new Diagnostic Oil Wipes.

The wipes are designed to determine the basicity (TBN) of a small amount of engine oil, the idea being what you’d wipe off your dipstick, within one minute. If the oil does not make the wipe turn pink, then the oil is acidic. Speed says that means fuel dilution is a possible culprit, and a larger sample should be sent off to a lab for analysis.

Outside of oil analysis results, signs of severe fuel dilution (greater than 4 percent) can include a hard start or rough idle, particularly with a carbureted vehicle, stalling, and a drop in oil pressure or power.

“But, if you changed your oil in the fall and left the vehicle alone, the amount of fuel in the oil shouldn’t have increased at all,” Speed says.

Fuel Dilution Graph (750x450)

As little as 5 percent fuel dilution — considered severe — can decrease the viscosity of an SAE 30 oil to SAE 20, reducing the oil’s life and its ability to protect engine components from wear.

Cranking your vehicle’s engine during storage allows fuel to mix with the oil, as colder operating temperatures, fuel system deposits or corrosion, or excessive idling can cause incomplete combustion. Any fuel that is not vaporized and burned then enters the cylinder, runs down into the crankcase and mixes with the engine oil. This applies especially to engines tuned to deliver a “richer” air-to-fuel ratio.

Running a few tanks of a fuel additive like Driven Racing Oil’s Carb Defender can clean deposits that promote fuel dilution, and help you determine if a mechanical issue is more likely to blame for the level of dilution present.

Running a few tanks of a fuel additive like Driven Racing Oil’s Carb Defender can clean deposits that promote fuel dilution, and help you determine if a mechanical issue is more likely to blame for the level of dilution present.

Additional ways fuel and oil can end up in the same place include blow-by and Exhaust Gas Recirculation (EGR).

“Despite the best efforts of the piston rings to keep 100 percent of the intake charge and combustion gases sealed, some percentage of these gases leak past the rings,” Speed says of blow-by.

With EGR, a process employed to reduce gas emissions, exhaust gases are mixed back into the intake and, thus, reintroduce unburnt or partially burnt fuel.

Speed adds that only in diesel engines, diesel particulate filters have been observed to increase fuel dilution due to an injection of extra fuel late in the combustion cycle to burn off trapped exhaust soot.

If you find signs of fuel dilution or get it confirmed through oil analysis, there are some simple steps to address the problem — and panicking should not be one, says Speed.

“Both injectors and carburetors are prone to getting deposits that can affect atomization of the fuel, and most modern pump fuel does not have a top tier detergent package to clean the injectors or carburetors,” he says. “This is where using a fuel additive is very helpful. Run a couple of tanks with a premium injector- or carburetor-specific additive, and then take another oil sample. If the fuel dilution is still above average, then it is time for a mechanical inspection of the engine.”

Even if your engine has not fallen prey to fuel dilution during storage, Speed still recommends use of a fuel additive to clean any deposits or corrosion that may have occurred while the vehicle was out of regular operation.

“If you didn’t put in a product like Carb Defender before storing, you can easily get fuel dilution in the Spring,” he says. “The deposits formed through the period of storage can cause fuel dilution as you begin to operate the engine.”

Source: Driven Racing Oil, drivenracingoil.com

About the author

PPN Editor

Power & Performance News is the source for news, tech and products that help you get more performance from your vehicle. If powertrain performance projects and hardcore technical content are your interest, Power & Performance News is the publication designed for you. Our acclaimed editorial staff covers all aspects of engine and driveline upgrades with a mission of presenting information that is both interesting and achievable for the “average car guy”.
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