i have 1989 300ce, manual requires premium fuel but...can i use regular without harming the engine - what will happen??

 

I had the same delimna but calculated (after many highway miles!) that the extra cost of the premium fuel was more than offset by the increased fuel economy by 1-2%. Almost negligable but economically it made sense to run premium and alsonot have to worry about harming the engine with regular octane.

This was a 2000 E430.

Matt