According to the November, 1999, issue of Lubes-n-Greases Magazine, OEM manufacturers are starting to allow equipment users to extend drains to intervals that synthetics will allow. This is clearly evident from tests of high performance lubricants conducted recently over a multi-year period by Mobil and Caterpillar. As reported in an Society of Automotive Engineers (SAE) technical paper, the companies used two grades of conventional diesel engine oil and two synthetics: one formulated to exceed API CG-4 and one to exceed CH-4, in 59 different engines. The authors report that "the premium, fully synthetic diesel oils were found to provide good engine protection with drain intervals as long as 45,000 to 60,000 miles (three to four times the engine builder's standard recommendation) depending on engine type. And engine inspections conducted after 500,000 test miles confirm that the extension of oil drain intervals with premium diesel engine oils has no negative impact on engine durability.

"In addition, the fully synthetic SAE 5W-40 oils evaluated were found to provide approximately a 3 percent reduction in fuel consumption relative to conventional counterparts."