Wich motor oil to buy

What are you planning on doing?
You do not "refuel" with motor oil. After a 10 second cursory browsing of your history, I can understand English is not your primary language - no worries! "Refueling" a car would refer to the adding of FUEL, which is gas/petrol or in Deutsch: Benzin/Kraftstoff. You are referring to Motoröl, which you simply "do an oil change" or "replace the oil". Saying the word "refuel" might confuse English speakers and lead them to think you are attempting to put Motoröl in your der Tank.
You forgot to include the year of your Mercedes, which is important in helping identify the oil specs. I suggest you simply go to a local Mercedes Benz dealership's "Parts Counter" or Service Desk, where you can directly order/request for parts and accessories. Give them your VIN number and they will look up the oil, and get it off the shelves and give you all the oil you need, along with the drain plug crush washer.
Drain plug is M14 so you want to get a socket wrench and maybe a cheap torque wrench from Harbor Freight so you can torque it to spec. Ask your Mercedes Benz Parts Desk clerk for the torque information as well!

Cheers.

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carb0nxl@reddit

I mean, I did use GPT for the English-to-German translations but that's it.

Where were you going with that statement?

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AdEnvironmental1953@reddit (OP)

Thanks for all the comments (instead of the liquid one :-)) Just found the last service document and found out, its 5w-40.

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If there's a Mercedes dealer near you, the actual MB 5w-40 isn't very expensive. I think it's somewhere around $7/qt and you'll be sure that it's the proper oil that way. Otherwise, Mobil 1 0w-40 should be just fine. I work on many MB.

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NewYearNewAccount165@reddit

Make sure you get the right spec and the it meets MB. You’ll want oil engineered to handle low speed pre ignition and extended intervals if you’re following just what MB says.

Personally I wouldn’t go over 8000miles on even the best synthetic oil but your driving habits are the leading factor. All city with lots of cold starts - change way early. Mostly highway and lots of time spent at operating temp - extend the interval.

I personally change my oil 8000kms/5000mi because I’m all city. Lots of fuel dilution

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mr_lab_rat@reddit

Assuming you need to top it up look for full synthetic 0w30 for European cars. It should have Mercedes Benz certification listed on it. It will say something like MB 229.71

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AirCommando12@reddit

You can’t just generalise all European cars as 0w30. In fact I’d say that would probably be wrong more often than it will be right

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C-coli85@reddit

I'm only putting this here because of your use of the word "refuel". Oil does not go in the gas tank, it goes in the engine.

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PotatoDrives@reddit

For a European car you definitely want be using EVOO

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Thatguy_9671@reddit

No i think that only applies to Alfa Romeo

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super_starfox@reddit

Are you topping off from being low? Doing a full oil change?

When it comes down to this, the year/make/model and specific engine matter. As another Redditor said, it's potentially located on the oil filler cap, but not always.

If it is, then the oil weight/viscosity would be labeled like 0w20, or similar.

Some cars, especially German (don't get me started, lol) won't have it printed directly on the cap. Other times, the filler cap gets replaced because reasons and is generic.

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SophisticatedVagrant@reddit

Should either be directly written on your oil filler cap or somewhere on a label under the hood. Otherwise, in your owners manual. Or, you could just google it...

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importfanboy@reddit

Liquid one