Is it Safe to Add Two-Stroke Oil to my Diesel Fuel?

Robert Gordon wants to know, via our Facebook page, if it’s worthwhile to add AMSOIL SABER Synthetic 2-Stroke Oil to your diesel fuel.

First, thanks for the question, Robert. Second, you’re not that Robby Gordon, are you?

For the uninitiated, Robert’s question alludes to a practice among some gearheads of adding a dash of two-stroke oil to their vehicle’s fuel tank to lubricate the fuel system and upper end of the cylinders. Sometimes, people use regular motor oil, too.

The fuel system and upper end of your engine requires lubrication to resist wear and last as designed, which the diesel fuel is supposed to provide.

There are waxes in diesel fuel that lubricate the fuel pump and injectors, helping fight wear. Without them, the highly engineered components in modern diesels, particularly high-pressure common-rail (HPCR) engines, can wear out or develop deposits that interfere with an optimum spray pattern, reducing power and fuel economy.

Reduced lubricity of ULSD

The problem, however, is that today’s ultra-low-sulfur diesel fuel (ULSD) provides significantly reduced lubricity – a critical property in controlling fuel-pump and injector wear. The ASTM standard for diesel fuel, D975, controls a minimum level of lubricity. Unfortunately, it’s not as much as the Engine Manufacturers Association (EMA) would like.

Since 2006, nearly all diesel available in North America has been ULSD. Why? Because the government mandated reduced sulfur to curb harmful emissions. ULSD contains a maximum of just 15 ppm sulfur, compared to up to 5,000 ppm some diesel fuel used to contain prior to EPA regulations. ULSD also is compatible with modern exhaust treatment devices, such as diesel particulate filters (DPF), that also help reduce emissions.

I doubt anyone among us will object to cleaner air. But ULSD can have the negative side-effect of reduced lubrication for diesel fuel pumps, injectors and the upper end of the engine. Since a full-blown injector replacement can cost thousands of dollars, some enthusiasts have been known to add a little two-stroke oil to the fuel to replenish its lost lubricating properties as a precaution.

But…is it safe?

In general, yes, but it’s not recommended.

Instead, use a fuel additive designed to keep the combustion chamber clean and lubricate the fuel system, like AMSOIL All-In-One or AMSOIL Diesel Injector Clean. It works better and it’s far easier to use compared to metering out a few tablespoons of two-stroke oil and finagling it into the fuel tank without getting half of it on your beautiful truck, not to mention your pants.

Both additives are formulated to offer the following benefits, which is exactly what every diesel truck or piece of equipment needs:

  • Cleans dirty injectors
  • Lubricates pumps and injectors to reduce wear
  • Extends fuel-filter life
  • Improves fuel economy up to 8%
  • Combats fuel-system corrosion
  • Prevents wax settling during storage
  • Lowers cold filter-plugging point (CFPP) by up to 40ºF
  • Delivers maximum horsepower
  • Increases cetane up to 4 points
  • Safe for use in all diesel fuels, including biodiesel
  • Alcohol-free

So, as much as I love the “do-it-yourself” independence of concocting your own solution to the problem of insufficient diesel fuel lubrication, it’s best to leave your chemistry set in the garage and just use one of our fuel additives formulated specifically for diesel fuel.

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