Hi! My car is 1996 Subaru Legacy L AWD. I find resently the MPG of my can is very low(~15MPG). It should have a MPG of 22 in local and 27 on high way. I drive mostly in local. I have this car from Aug. 2006. I changed the oil on Aug.29, 2006, and have ~2,500 miles on it. Is the low MPG caused by the oil or the low temperature in winter? Should I change the oil every 3 month or every 3,000 miles?
There ae so many variables that can affect fuel economy. Everybody has a different opinion on oil changes.I recommend 3k or 3 months but that is a guideline. Heres the deal not all of the fuel that goes into the engine is burnt as part of the combustion process. That fuel ends up in the crankcase with the oil. As the engine warms up the fuel in the oil evaporates or is reburned by re-entering the intake manifold. In cold weather the oil in the engine has a tough time getting to the tempature needed to start that fuel evaporation process. The longer this goes on the more fuel the oil collects compounding the problem. On a Subaru the engine can collect more fuel in the oil due to the design of the engine. The best thing you can do to help fuel economy is let the engine get to full operating temp as much as possible. This is where the best fuel economy is acheived and where your car will pollute the environment less.