I've used Mobil 1 in 0W-40 in my Porsche for years and experienced no internal engine problems. Of course I would expect the same of any brand name full synthetic with appropriate ratings. My MB dealership uses Mobil 1 in 5W-40 in my GLA.
For premium fuel I use whichever brand is lowest price locally at the time. I've not noticed any difference in performance or MPG with any.
I haven't tried E85 in my GLA. Cost is usually less than $1 cheaper, so with E85's reduced MPG expectations, doesn't make economic sense. Anyone out there try E85 in your GLA yet? Would like to see some comments from GLA owners on their experience with E85.
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