oil advice

[moss]

i have been using shell rotella synthetic 5w40 in my 1997 e320 mercedes for the last 40k miles, but i feel like i would get better gas mileage if i went with Mobil 1 0w40. engine has almost 200k miles, smooth as silk and doesn't use a drop of oil between changes. i have always been getting 17-18mpg all city and 27-28mpg all highway, but my friend with same year/model gets 20mpg city and 30mpg highway and he uses Mobil 1 0w40. what do you guys think, would it make a difference if i switched oils, or just stick with what i have been using?
my engine takes 7liters of oil, and i still have 1 gallon of rotella 5w40. is it ok to mix it with Mobil 1 0w40?

 

[Steve S]

Don't mix the oil. It is o.k. to do so but how can you tell if there is an improvement with the oils mixed. I do not think the difference in viscosity would make much of a difference unless it is really cold but you might like the Mobil 1 oil.

 

[Rand]

Its probably driving style, climate, what driving he does or something similar..

even the best oil would only net you < 1mpg

I'm talking switching from say.. 20w50 to 5w20 = 1 mpg or less

certain exceptions apply.
like say you made all 2mile trips in the winter etc

 

[moss]

thanx for the quick reply. you think Mobil 1 0w40 is a better oil and would be better for my engine at start ups during cold winter months?

 

[Petrou]

i think so. not really a big change but still better for cold startup