I would have to agree with most of this but I think age of the also plays into it. My 240s run better, better mpgs and smoother idles with premium fuels, especially from racetrac. The HEMI XK was also sensitive to the fuel brand I ran in it, Sunoco was best I tried. I would have to believe this is based on what/how much additives are being used. I've never heard of using higher octane to "clean" the system but have heard of using name brand fuels rather than your eco fuels. I'm also I big fan of Techron, my family has used it in all their vehicles

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