This truck was Bulletproof for about 10 years, then all of a sudden the engine started making a really loud knocking sound. When I check the dipstick it was almost completely empty of oil. There was never any leaks or black smoke coming out of the truck. I had it serviced and they made some expensive changes that fixed nothing. I have to keep dumping a quart of oil in every 300 miles. I don't know what caused this, I get the oil changes and tune-ups regularly. This truck is carefully maintained. Too bad, this was otherwise a pretty solid truck for a long time.