Green Transport Partnership
A Glance at Clean Freight Strategies:
Low-Viscosity Lubricants
Synthetic
lubricants are a
low-cost way
to improve fuel
economy and
reduce
emissions.
What is the challenge?
Friction losses in a truck's drive train (transmission and differential) and its engine waste
energy and reduce fuel economy. Friction losses can be reduced through the use of low-
viscosity lubricants. Most manufacturers of lubricants produce "fuel economy" brands
that have lower viscosity than standard lubricants. Many fuel saving brands are
synthetic lubricants, although some mineral oils can also improve fuel economy.
What is the solution?
The American Trucking Associations' (ATA) Maintenance Council claims that synthetic
transmission and axle lubricants improve fuel economy by 0.5 percent in the summer
and two percent in the winter (when mineral lubricants experience higher viscosity).
Replacing all-mineral transmission lubricants with low-viscosity products saves fuel
with little or no additional cost. Low-viscosity lubricants have a lower resistance to
flow than standard lubricants and thus can help to inhibit the energy loss due to drag
that is common to high viscosity oils.
Use of synthetic engine lubricants also provides fuel economy benefits. Several
studies have found good results:
• A recent Society of Automotive Engineers (SAE) paper found that synthetic
lubricants used in the engine and transmission provided a five percent fuel
economy improvement, with greater gains at lower speeds.
• Another SAE paper found that synthetic gear lubricants improved fuel economy
by 2.6 to 3.3 percent.
• A study in Europe showed that single-unit freight trucks can reduce fuel
consumption by 4 percent using 10W-30 engine oil instead of 15W-40.
• Another researcher in Europe showed a 3 to 5 percent gain in truck fuel economy
using low friction engine lubricants and a 1 to 4 percent gain using low friction
transmission lubricants.
Semi-synthetic or fully-synthetic lubricants typically cost more than conventional
mineral lubricants. Truck service stations suggest that semi-synthetic oils cost about
50 percent more than conventional mineral oils. Some transmission manufacturers
recommend synthetic lubricants for all their products for reducing wear and
maintenance. Since synthetic oils usually meet the American Petroleum Institute (API)
and ASTM standards, they do not void the truck warranty. Most engine manufacturers
Office of Transportation and Air Quality • Mailcode? • October 2002 • EPA 420-F-02-020
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recommend that users follow the recommended oil change frequency with both
synthetics and conventional oils, even though many recognize that synthetic oils may
last longer. Truck owners should always check engine manufacturer specifications for
lubricants before switching engine oils.
The results are in.
The combined effect of low-viscosity synthetic engine oils and drive train lubricants
can improve fuel economy by at least three percent, saving nearly 500 gallons of fuel
per year for a typical combination truck. Factoring in the increased cost of the
synthetic oil, truck owners will still save approximately $180 per year. Switching to
low-viscosity lubricants will reduce greenhouse gas emissions by five metric tonnes
per year for each truck.
Next steps
Truck owners should consult their vehicle owner manual and engine manufacturer
specifications for acceptable lubricants before switching engine oils. Synthetic oils are
compatible with most engines and drive trains and usually provide fuel savings that
offset their higher cost. They should be utilized in accordance with engine
manufacturer recommendations for oil change frequency to achieve cost savings
while helping to reduce our dependence on foreign oil and damage to the
environment.
For further information, ATA's Technology and Maintenance Council and the Engine
Manufacturers Association can provide information about the relative benefits of
various oils. Lubricating oil manufacturers can also provide information about the
potentially less frequent need to change oil with some synthetic lubricants.
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