ABSTRACT The US Army is currently seeking to reduce fuel consumption by utilizing fuel efficient lubricants in its ground vehicle fleet. An additional desire is for a lubricant which would consist of an all-season (arctic to desert), fuel efficient, multifunctional Single Common Powertrain Lubricant (SCPL) with extended drain capabilities. To quantify the fuel efficiency impact of a SCPL type fluid in the engine and transmission, current MIL-PRF-46167D arctic engine oil was used in place of MIL-PRF-2104G 15W-40 oil and SAE J1321 Fuel Consumption In-Service testing was conducted. Additionally, synthetic SAE 75W-140 gear oil was evaluated in the axles of the vehicles in place of an SAE J2360 80W-90 oil. The test vehicles used for the study were three M1083A1 5-Ton Cargo vehicles from the Family of Medium Tactical Vehicles (FMTV). The M1083 utilizes a Caterpillar C7 ACERT engine, an Allison MD3070PT 7- speed automatic transmission, and Rockwell/Arvin-Meritor 7.8:1 ratio, single reduction, amboid gearing, bevel wheel end reduction axles. Each test segment consisted of vehicle operation over a 67.6 km (42 mile) course at speeds of 40.2 and 80.4 km/hr (25 and 50 mph). These speeds where chosen to be representative of actual military vehicle usage in convoy type operations. Each test segment was compared to its previously run baseline for fuel consumption comparison. A fuel consumption improvement was demonstrated for reduced viscosity lubricants in both the engine and transmission test segments. INTRODUCTION The U.S. Army desires to increase the fuel efficiency of its ground vehicle fleet. One potential area for fuel consumption improvement is found in the lubricating fluids locatedthroughout the driveline. By varying the lubricating fluids used in the vehicles drivelines, a potential reduction in mechanical losses can be achieved. These mechanical losses can occur in many forms including frictional, pumping, and churning losses, and are very dependent on the fluid's chemical/physical properties and the equipment design. A small increase in the overall driveline efficiency could have a significant impact financially when multiplied over the entire U.S. Army vehicle fleet. In 2008, an average of 68 million gallons of fuel a month were consumed by military forces in Iraq and Afghanistan alone [ 1]. Increased efficiency provides both the typical financial benefits experienced by commercial users and a reduction in transportation and logistics costs in providing fuel to deployed vehicles around the world. Additionally, the extended drain capabilities of a SCPL would reduce costs associated with transportation of lubricants and man-hours for oil changes. This investigation looked at the fuel consumption effects of low viscosity, synthetic engine, transmission, and axle gear lubricants as used in 5-Ton Cargo M1083A1 variant of the Family of Medium Tactical Vehicles (FMTV). These fluids have shown fuel consumption benefits in the past [ 2,3,4]. Fuel consumption changes were determined according to the Joint TMC/SAE J1321 Fuel Consumption In-Service Test Procedure - Type II [ 5]. Information from this investigation will be used to quantify the fuel efficiency benefits of the candidate lubricants. APPROACH There are many options for testing lubricant fuel efficiency. Tests range in complexity from engine fuel economy tests, such as Sequence VIB and CEC M111 for gasoline engines, to vehicles running long-haul style routes or comprehensive field tests. For the scope and budget of the project, and the Fuel Efficiency Effects of Lubricants in Military Vehicles2010-01-2180 Published 10/25/2010 Robert Warden and Adam Brandt Southwest Research Institute Allen Comfort and Luis Villahermosa US Army RDECOM-TARDECDownloaded from SAE International by American Univ of Beirut, Sunday, July 29, 2018desire to get data that was as close to real world as possible, it was determined that in-vehicle testing would be the best option. The vehicle platform