London is SO expensive, but it can be done! That wage sounds pretty darn good to me!
Driveupcoffee is right - rent is what really destroys your soul when you first move here. But looking a bit outside of London helps if you're willing to spend a half hour or so on the train. We have a two bedroom semi with a big garden for the same that we'd probably pay for a one bedroom in a crummy part of London - but it's about 35 mins by train to Marylebone station....
Another thing that's helped me a lot is to do the weekly shop online 'cause then you can see what you're spending and adjust it accordingly before you actually check out.... My average weekly bill is somewhere around £40 for two people (one of them being a very big eater!
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Cocktails are going to set you back a lot - I'd aquire a taste for ale, lager, or "dry white wine" as quickly as possible (off topic - why do so many women drink "dry white wine" in the south? Visiting my friends in Leeds always makes me so aware of how uncommon it is to see girls drinking pints down here!)
You mention oil changes - I would personally avoid having a car if you're going to be IN London - it's a necessity if you're outside a big city, but in my experience London just doesn't require a car. Besides, gas/petrol is SO expensive, plus MOT (the yearly test to assure your car is road worthy), tax, and insurance - it's pretty outrageous. Public transport passes are expensive too, but pretty darn convenient.
Cheap entertainment isn't super easy to come by, but it can be done, and it's fun exploring around for reasonably priced places. I use the Itchy guide to London - it's full of restaurants, bars, etc. and has loads of great recomendations of places off the beaten path and more reasonable in price.