Motor Oil Info

Because diesel fuel is a natural solvent, it causes a multitude of problems when it contaminates the oil, including reduced oil viscosity, reduced oil film strength, increased engine wear (particularly in the cylinder/ring area), increased volatility, weakened lubricant detergency, accelerated lubricant oxidation, varnish formation, acid formation/corrosion and low oil pressure.

The most notable problem associated with increased fuel contamination is reduced viscosity and the corresponding effect it has on oil performance. When combined with shearing conditions, as little as 4 percent fuel dilution is generally enough to reduce an oil’s viscosity to less than the specified viscosity grade.

AMSOIL sent five competitive synthetic CJ-4 5w-40 diesel oils to an independent laboratory for shear stability testing. Knowing the tough environment that diesels present to lubricating oils, AMSOIL doubled the standard Kurt Orbahn 90-cycle test and had the oils tested for 180 cycles. Samples were then contaminated with 2 and 4 percent ultra low sulfur diesel (ULSD) fuel. As the graph shows, even after being shear tested for twice the industry standard and contaminated with 4 percent fuel dilution, AMSOIL maintained viscosity and was the only oil to stay within an SAE 40 viscosity rating. As other oils lost viscosity due to shearing forces and fuel dilution, their ability to protect against wear was jeopardized.