hi moontan, for the past three and a half years I have worked as a mechanic at my family owned business (which my father has ran for 25 years) and I have seen a lot of cars with internal engine problems, but to make this story short one incident that I remember was with a 1986 Chevy S-10 4x4 with a 2.8 V-6. It came in with a blown motor and the owner didn't know why. After we got the engine out we were going to drain the oil in it as we do in all engines we take out and when I took the drain plug out nothing came out. After it sat there for about 15 or so minutes big glops of grease or so we thought started to come out. At first we thought that this person just never changed his oil. Later when the person came to get his truck we told him of our incident and asked him how often he changed his oil and he told us that he changed it every 3,000 or less miles and he even proceded to show us the bills that he kept in his truck that he had for his records. But what caught our eyes was that the place he took it featured Pennzoil and Quaker State which are the same company.So to conclude our theory we figured since when he got his oil changed the truck engine was hot the oil was thinner and when the oil cooled down it became thick like grease. So from that day on he has never used either brand in in all truth I don't recommend it either. If you were to ask me what to use I would say either Castrol or Mobil (I own a 1999 Subaru Impreza and I use Castrol Syntec 5w-30 in it) Just stay away from Pennzoil and Quaker State!