To comment on the motor oil, Voltronic 5W40 meets MB 229.5 specs. I have tried another German motor oil Addinol 5W40 on my W220 (S320), but it runs rougher and burns at least 7% more gasoline on highway driving. The Ester based Voltronic is a much better motor oil at high RPM, and the car feels lighter and much smoother.
Another thing I want to point out is the ATF used on S320. The original one is not fully synthetic, so use fully synthetic such as Voltronic 9K. The S will give much stronger acceleration, and the 5 Speed gearbox will last for 300,000 KM if change the ATF every year. Especially for the hilly roads & stop and go traffic in Hong Kong island.
Overall, this is a very good car, but the airmatic can be expensive to replace. And the earlier versions 99 or 00 have poor conditioning and is not reliable for hot climates.
The interior is not very solid, and some eco friendly plastic parts break every 2 to 3 years, although they are cheap and easy to replace.
This is a very good car for the money, and many billionaires in Hong Kong have one. You can drive this car for shopping or even fishing, or to the 5 star hotels and you are always well respected. You can park it next to the British Racing Green Rolls Royce Fleet at the Peninsula Hotel, and still do not feel out of place!
The S320 is overall a very good car for the family and business. The design is over 10 years old, but the shape still looks quite aero- dynamic and yet classic.
The V6 does run smoothly, and is quite economical for highway use. It can easily average 30 miles per gallon if cruise at 60 MPH. I switched from Mobil 1 0W40 to Voltronic 5W40 fully synthetic motor oil, and now can get 32 miles per gallon. My mechanic has told me that Voltronic (an OEM Mercedes product) also comes in 5W50 and 10W60.
This is a modern car for its period, and is still not outdated until today. A lot of first generation environmental plastic parts were introduced to this car, but they were not as durable, and they break down in a few years, but Mercedes has made better replacement parts.