I just buy a mazda cx7 2007 model and I ask mazda to roadworthy it for me and do a diagnosis by a qualified technician , the out come was that...

I just buy a mazda cx7 2007 model and I ask mazda to roadworthy it for me and do a diagnosis by a qualified technician , the out come was that there was some leaks and that the timing chain was on its way out , the car had only 180000, km on it , now I did plan on booking the car in , but I had my own qualified tec look at it when it got back from the roadworthy and he told me it should not have pass , I then took it back to mazda and they in formed me they made a human mistake , they then made sure the mazda tec look over it again , ( I am sure he did not do it the first time ) anyway he came back with a report that identify the problem with more oil leaks and some rubbers , now mazda fix the rubbers and did not charge me anymore as it should have been cover'ed under the roadworthy , now my daughter has been driving the car around for another 3000, km be for we could book in back in with mazda , I followed my daughters car from my house to geelong where the mazda dealership is there was no smoke coming out of the exhaust and there was no noise what so ever in all that time , this was on a Monday morning they say it would be ready by Friday , it would only take 6 hours to fix the new timing chain , come Friday they then tell me it wont be ready until the tusday but there was a added problem , the car had used 4 Lt of oil and now is making a knocking sound at the bottom end , I can only assume they had been driving it around , so the real question is can a car like that burn that much oil in only 3000, km and not blow any smoke and I do mean any smoke ?