My car is blowing blue smoke all the time. what is the problem ?

Blue smoke is oil burning. Most likely engine oil. It is commonly worn or dirty piston rings or worn valve seals causing your engine to burn excessive amounts of oil. A complete diagnoses of your engine may be necessary to determine the cause.

If it takes a while for it to start to smoke you could have clogged oil return passages that lead to the oil sitting on top of the engine and the oil going right down the valve guides or perhaps bad valve guide seals that have deteriorated over time , Fords are known for this , the for sure way is to do a compression test both dry then wet , then check the oil pressure to evaluate whether the engine is healthy or not , and another way is to read a vacuum gauge , that could tell a lot about the condition of the engine , this is almost a forgotten skill that most mechanics don't practice , hope this helps , Kevv

Check this information on blue smoke that comes out the exhaust http://www.cartechhome.com/2008/02/blue-smoke-coming-out-of-exhaust-system.html