Base oils have not changed but the formulation and synthetics have changed the oil world. All oils are good but the protection the synthetics offer is superior to regular blended motor oil. When we consider which weight of motor oil to use, some of the important specifications are the pour point, the flash point and viscosity Index. When we compare a synthetic to conventional motor oil weight the numbers tell the story. Just picking a popular brand like Valvoline conventional oil and their synthetic oil, in the 20w-50 and 10w-30 oils
Concerning the numbers: 1. Pour point-the lower the better 2. Flash point-the higher the better 3. Viscosity index-important number-oil consistency to flow, again the higher numbers better, indicates a low change at temperature.

-------------------- Pour pt. Flash pt. Viscosity Index
20w-50
Conventional All Climate -10F____430F___125
Valvoline Synthetic ___ -40F____ 465F__ 146

10w-30
Conventional All Climate -26F___410F____130
Valvoline Synthetic ____-40F___450F____140

And Mobil a popular oil with MB owners
20w-50.
Conventional. ________-17F___392F___124
Synthetic 15w-50 ____-45F___ 446F___153

10w-30
Conventional _________-33F___392F___134
Synthetic ____________-45F___471F__ 147
Synthetic 0w-40 ______-54F__ 471F___187

As I mention, for me synthetic oil’s is the best lubrication for your engine, and by reviewing the numbers you can use any synthetic weight in your car all year. But if I lived in a extreme cold climate area my old ways would say use a 10 or 5w- 30 oil, or most likely use one of the new weight oils 0w-40, 5w-40 or 5w-50. It seems in my readings that Oil Company’s in the last couple of years are producing improved engine oils. What weight, I’ve always used Mobil 1 15w-50, but I'm considering the switch to 0W-40, better start-up protection, better protection at high temperatures-and yes better mpg, and that high viscosity number of 187 for overall lubrication.
Enjoy your drive, timreid

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timreid
1992 400E
euro lights
500E sway bars
210 16in wheels