i had just bought mobil 10w30 synthetic blend for $1.99/quart at kragen. Im planning to use it in the S420 once the next oil is due for a change, currently it has mobil 1 5w30.

It seems as though the car gets better mileage with a synthetic. And this was the same with my diesel. Back when i had the 300SD i used delo 400 15w40, performance wise it was the same clackity ol diesel. But when i switched the the 5w40 synthetic my mpg's went up and the cold starts were better.

Id say the best choice would be either a full synthetic or a synthetic blend. But a synthetic blend that wasnt done by mixing two different oils even if they were both of the same weight and brand.

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Current:
05 E320 CDI
07 GL320 CDI
08 Sprinter
05 Dodge Cummins
01 Dodge Cummins

Previous
2004 E55 AMG
2002 C32 AMG (#2)
1995 E300
1978 300D
1987 300D
2002 C32 AMG(blown motor :[
1981 300SD
1983 300SD
1987 300SDL
2002 Jetta TDI
1996 S420
1995 S500
1993 190E 2.6
1992 190E 2.3
1985 190E 2.3 5-Speed