Mercedes-Benz E280 Engine Problems
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The Mercedes recommended fuel for the E280 is 91-octane regular unleaded, while the recommended fuel for the C180 Kompressor is 95- octane premium. While you can safely run the E280 on regular unleaded, and I suspect you could run the Kompressor on 91-ocatane, you will get better performance and economy by running them on the higher-octane fuel. Mercedes-Benz also approves the use of E10 ethanol blend fuel in both of your models, which might help you save a few pennies.