I have a 2001 Ford escape with 64,000 miles. I have had my oil changed at jiffy lube the last 3 times and they have added 5W/30. My engine is now ruined, per my mechanic. The piston is firing up too high and hamering my plugs. He told me that the oil grade was most likely the issue. The vehicle is undrivable, and there is no longer a warranty on it. have there been any other cases where the wrong oil WILL damage the motor? I have treated this vehicle very well, and have not expected anything outrageous of it. Does anybody have any useful info for me? I am intending to try to get Jiffy Lube to pay for the new motor if i can, but I do need more information before going to them.