Subaru requires Subaru  Synthetic 0W-20 motor oil(or equivalent) for the new non-turbocharged engine in the 2011 Forester and requires Subaru Synthetic 5W-30 motor oil (or equivalent) for its 2011 turbocharged vehicles. Here’s why.


Challenges Posed by the Modern Engines


The new FB SUBARU BOXER four-cylinder non-turbocharged engine in the 2011 Forester was designed and engineered for improved fuel economy, a wider range of power, and improved response. The design puts different demands on engine oil. (See “The All-New Subaru FB Engine” article in Winter 2011 Drive.)


Turbocharged engines also place unique demands on motor oil, exposing it to extreme heat and high engine speeds. These tend to break down conventional oil more quickly. Turbochargers operate at higher temperatures, which can lead to restricted oil passageways and deposits on the turbine shafts if the engine is not maintained properly.



As a result, Subaru 0W-20 synthetic motor oil (or equivalent) is required for the FB engine and Subaru 5W-30 synthetic motor oil for Subaru 2011 turbocharged engines. Subaru synthetic 0W-20 is uniquely formulated to handle the low-friction design of the FB engine, while Subaru synthetic 5W-30 is formulated specifically to address the harsh demands of a turbocharged engine. For 2010 and earlier turbocharged engines, Subaru also recommends the Subaru synthetic 5W-30 motor oil.


Synthetic Oil – More Refined


Conventional and synthetic oil both are produced from crude oil. Their differences lie in how they’re refined.


A synthetic base oil can be produced by using two different processes. Both processes start with crude oil. The first process separates and breaks crude oil into small molecules and then uses polymerizations (forming larger molecules from two or more molecules by a chemical reaction) to derive a synthetic oil base from crude. The second process refines crude oil into conventional base oil and then undergoes hydrocracking (breaking crude oil’s heavy hydrocarbons into lighter products in the presence of hydrogen) and hydroisomerizing (changing hydrocarbon compounds into a different molecular form).


Additives mixed with the synthetic base oil enhance its performance. In its final form, synthetic oil is approximately 80 percent synthetic base oil and 20 percent additives.

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