masterianvii

My C55 tells me to add a quart of oil. The last time I did service, dealer sold me Mobile 1 5w-40. For some odd reason, the only oil I can find in my neighborhood is the ultra hard to find 0w-40 229.5 MB approved. (Funny how life works.)

Is it ok to mix the two? It's the same formula, just different weight. I imagine I'll end up with something like 4.5w-40 .

boschk

No issues to mix the two.

For the C55L

Engine Oil
Grade 1......SEO[1]
Performance Synthetic 5W-30 European Oil (AELQT)
Performance AMSOIL European Car Formula 100% Synthetic 5W-40 Motor Oil (AFLQT) Above 5 F......15W-40, 15W-50
Above -4 F......10W-30, 10W-40, 10W-50, 10W-60
Above 23 F......20W-40, 20W-50
All TEMPS......0W-30, 5W-30, 0W-40, 5W-40, 5W-50

M-bENZ

0W-40 all the way....just changed mine 2 hrs ago,

Autotechnica

Although 0W40 is recommended, 5W40 is used more commonly and stocked by more shops since it's a bit cheaper as well. 5W40 is used by Mercedes dealerships here in Ontario, Canada. I've contacted Mobil 1 a long time ago about using 5W40 instead of the Merc recommended 0W40. Their response was that they suggest 0W40 for the winter months for smoother start up. 5W40 is fine for summer months or in countries/states that have mostly warm weather. Remember that the number before the "W" is the rating for winter weather viscosity which simply affects cold start up. I rarely drive my C32 in the winter, so I've always used 5W40 and so has my dealership.

Anyways, mixing the two viscosities is fine.

Bry

masterianvii

Thanks. Looks like other sources on the internet also confirm that mixing oil weights is fine, as long as the difference in the weight is not significant and it's the same type of oil. For example, ok to mix 0w40 with 5w40, not ok to mix 5w30 with 20w50. The reason from what I read being that that different viscosities have different properties. I'm not a chemist, so I don't know for sure, but almost everyone I asked, and everywhere I read, this combo works. Plus it's mentioned somewhere on the mobil1 FAQ site.

ruben65

I just had my oil changed at the dealership and they used 5W-40.

The first number with the "W" refers to the oil's cold temperature viscosity rating, while the second number refers to the oil's high temperature viscosity rating.

Oil Viscosity Chart for Temperature References