Volvo: Blue smoke on start-up, 850 T5, valve seals, piston rings

Question
Hello Nigel, I have recently purchased an volvo 850 T5, it was fine when I bought it up until I serviced it my-self. I carried out a standard service (filters, plugs, oil, ect...) BUT when I filled the engine with oil (shell 10/40) I overfilled it by about 1 litre without realising!!! I drove the car for about 5 miles to give it a test run, and checked the oil level when i stopped. I quickly drained the oil and filled it to just below the max line. But now, every time I start the engine, it puffs out a large amount of blue/white smoke? there is no sign of oil in the water or visa-versa? It dissapears after about 30secs of driving and the car drives perfectly.Would you have any idea what the problem is?
Thanks alot
Tom Green  

Answer
blue smoke is caused by leaking valve seals or piston rings
and you say it just started doing this, if it doesn't go away either you spilled oil on something that gets hot or you damaged a valve seal, which is kind of unlikely, white smoke is a head gasket, putting an extra quart or so of oil shouldn't damage anything BUT some saavy people/dealers sell cars that have worn engines with quite thick oil to hide blue smoke problem, if it doesn't go away you need to put 20/50 in for the summer or half and half, and 15w40 for the winter (synthetic)this scenario would make synthetic in winter absolutely mandatory