Many Mercs specify 98RON or higher in the handbook but "Temporarily, you may use 95RON, but this may reduce power and increase fuel consumption. Furthermore, please be advised that you should also avoid the use of full throttle should you choose to use such fuel"

Edited by Big John on 03/06/2017 at 09:09

All modern cars sold in the UK for the past 20+ years can run perfectly well on 97/98/99 octane super unleaded (apart from diesels, obviously), without any harm to the engine. Whether they get any noticeable gains in power or economy from doing so is another matter.