The last time I measured oil usage, it was about a quart of oil per 250 miles. Showed it to auto mechanics (twice, so far). They changed PCV valve (just in case, saying this is the most common cause) and checked everything thoroughly. There are no oil leaks, no noticeble oil burning or anything that could give a clue for where the oil goes. They performed some tests (I did not get what exactly they did, sorry), and were not able to detect any problem. So, I do not know what to do now, after they gave up. Does it make any sense to try and find the problem on my own (then, what to look for?)? Or should I seek an expert advice? (And from whom? It is such a waste of time to have it checked over and over again and find nothing.). Thank you.