Loss of mpg on 2006 legacy Subaru
A dirty air filter will prevent adequate air from entering the engine thus reducing gas mileage. Worn spark plugs or a weak spark (defective spark coils) can do the same. A defective "upstream" oxygen sensor (in the exhasut system) can lower fuel mileage. It forces the engine computer to guess at combustion efficiency without feedback from the sensor. It will err on the "rich" side to save the engine, which means it wastes gas. A "check engine" light will be "on" if that is the problem.
In winter, more alcohol is added to gasoline in cold climates to due to the lack of photosynthesis in the region (to make oxygen for us to breath.) Reduced fuel mileage results. Alcohol burns cleaner (and cooler) but it contains less energy (BTU) per gallon than "straight" gasoline. For example, E85 won't take you as far as a tank of regular gasoline.
If your car is designed to use 87 octane fuel, there is no need to use higher octane fuel. Higher octane fuels are for "high performance" engines with increased compression ratios. High octane fuel burns "slower" in the cylinder (to help avoid "detonation") so that the engine can take advantage is its greater compression ratio and advanced igntion timing to make more power. If your Legacy has a turbo, it will likely require the use of premium gasoline to avoid "detonation" under boost. Otherwise, "cheap", 87 octane gas is fine.
Feb 11, 2015 |
2006 Subaru Legacy