W210 E300TD Engine oil

[Parrot of Doom]

I've been recommended a 5w40 synthetic oil for my engine.

Currently it has 10w40 semi-synth in it, and after nearly 5000 miles its starting to get slightly clattery.

Just wondered what oils other people here use - and what a good oil change interval on 5w40 would be? I have 3 litres of the 10w40 left, would it be a good idea to drain 3 litres, and use what I have left to top the engine up for another 1-2 thousand miles before I change the oil?

 

[Blobcat]

Just wondered what oils other people here use - and what a good oil change interval on 5w40 would be? I have 3 litres of the 10w40 left, would it be a good idea to drain 3 litres, and use what I have left to top the engine up for another 1-2 thousand miles before I change the oil?

I use 5W40 synth (Mobil) and changes are in the 14-17K miles or every 6 months for me. ASSYST still gives me around 4K to service so it appears the oil is lasting the distance. I like 6 monthly oil changes, if I was not doing the 30-36K miles I would still do the oil changes.
Driving habits and type of journey can also have a great affect on oil quality, short journeys in cold weather will do more to 'wear out' the oil than long journeys. IMHO if you want to keep the engine going for as long as possible use decent quality Synth and change it regularly.
It cannot do any harm replacing 3 lts with your spare oil, it depends on when you were going to do the service really. You could always keep it for the mower.