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Why Does a Mustang Use Less Fuel Using Mobil 1 0W-40?
Ask Your Stickiest Question. . . Or ask us something you’ve always wanted to know about using our products. We’ll sort through all the submissions and present the best questions to our automotive experts. We'll share the questions and their answers here.
Why Does a Mustang Use Less Fuel Using Mobil 1 0W-40?
After reading many tech articles about oil, the API and European ACEA standards, I decided to start using Mobil 1 0W-40 in my Mustang GT instead of Mobil 1 5W-20. I like to rev it, and put a different high octane high performance tune in it. The European ACEA A4/ B4 tougher HS/HT standard gives me more peace of mind. I know ILSAC GF-5 stands for fuel economy. But why is it that since I started using 0W-40, my car actually uses remarkably less fuel?
-- Hans Smaling, Potomac, MD
Don’t mess with success, but technically this makes no sense. The Mobil 1 5W-20 synthetic oil should provide better fuel economy than the 0W-40.  The SAE 20 grade is less viscous under operating temperatures than the SAE 40 grade.
Updated April 2012
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