I have a 2005 ML 350 i now have about 78,000 mi on her i been using mobil 1 5/30 oil my question is which grade of oil should i be using

Probably one the the MOST frequent questions!

To me that depends on how long you are going between oil changes.
My fleet gets fresh oil & filter every 5K miles & I always use synthetic oil. (5W-30 or 0W-30).

I know the oil will last longer! BUT since I know how much it costs to replace an engine!!
My cars will get fresh oil before the old oil is shot.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I'm using diesel oil in my new to me 99 s320.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

You should be using motor oil that meets Mercedes specification 229.3 or 229.5

No other numbers on the oil bottle are as important as these, and the other numbers are in fact essentially meaningless.

Oil that doesn't have the Mercedes approval printed on the bottle is not suitable.

The easiest to find conforming oil is Mobil 1 European Formula 0W-40.

Because one version of Mobil 1 meets the requirement does not in any way mean they all do.

This information is in your owners manual, and if you don't have an owners manual you can get one at your dealer or by calling 800.for.merc.

See http://www.startekinfo.com/StarTek/outside/9511/?requestedDocId=9511

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Thanks for your info on the oil issue . I have been changing my oil about every 3 to 4000 miles.......

And you're not doing your engine or the environment any favors doing so.

Follow the factory recommended 10K miles interval, which is in fact VERY conservative.

It's the 21st century.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Ditto, Ikchris. Syn oil only, of course.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback