OK, I'll be the lone voice here.

We have a 1990 and a 1991 124. For all their lives I have mixed 50/50 premium/regular. I figure mid-grade is 89 octane, and my 87/93 mix makes 90 octane.

In the 400,000-plus miles between these two cars, at 10 cents a gallon or so difference, I've probably saved over $2000.

Never any serious engine work that had anything to do with fuel, but I did lose an oil pump once on the 1990 due to the carelessness of a mechanic who dropped a ball socket into the engine. Years later it finally broke thru the oil pump screen and locked up the oil pump.

Both cars have always averaged about 22 MPG.

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2012 E350
2006 Callaway SC560