i have a commercial heavy construction customer with a ford truck 4.6 that just needed an engine overhaul these guys run these things until the wheels rot off.. Well he uses ONLY cheap 5w30 he buys anywhere it is on sale cheap (he has a shop for his fleet on his property) this engine overheated bad and warped the heads and it let anti freeze into the oil.. he changes oil every 5 months and whatever mileage. On the front floor i saw a quart of S.T. a quart of sears and a mobil quart( he gets the sears cheap from a friend) This engine was not the cleanest inside and burned a little oil but was not so bad either i did make a comment to him that he should change the oil with one brand and do it every 5 months or 5000 miles,,, He said to me why and i said it would be better for the engines he said this one has one of the lowest miles some of the others have more The mileage is 335,993 ... he has one that has 400+ running good... He said cheap oil is just as good as the expensive stuff because it saves him money... I could not argue with him his equipment lasts forever on the cheapest oil.. Some say oil is oil i may be one of them soon