I suspect the reason there is so much suspicion and confusion about this topic is because most the information we get on the subject is from the folks that sell oil and, the manuals we have are making references and using information that is extremely outdated. Certainly, since the DeLorean was manufactured, considerable advancements have been made in lubricating technologies. I have personally fretted about this subject until I got some engineering information from a petroleum engineer friend some years ago and then did some reading on the subject. There are many factors that go into recommendations for an engine lubricant. The engine tolerances, operating temperatures, emissions, oil capacity, circulating efficiencies in the engine just to name some. But the goals are proper flow, protection at high and low temps, and cleanliness. Getting to the bottom line ? The DeLorean engine should use 40 weight oil. Whatever W you want to use for winter or cold weather starting should be based on your local conditions. In Houston 10W-40 works most of the time. In the Northeast (NJ) I use 5W-40 Synthetic. I would say for most locations and using conventional oil, stay with 10W-40. Actually there are probably 16 or so specifications one may want to review when deciding on an engine lubricant. However, you need not be that discerning if you stick to major brands like Shell, Valvoline, Pennzoil, Exxon, Havoline, etc. and yes, full synthetic lubricants are far superior to conventional oils. My personal experience - when I lived in Houston I drove a DeLorean everyday for ten years and over 80,000 miles I used 10W-40 Exxon. My petroleum engineer friend worked for Exxon and he showed me that, in convential motor oils, the add-pack was everything and only the majors had the quality control to do it right. The oil and filter was changed every 3-6,000 miles depending on when I had the time, etc. However, today I use full synthetic 5w-40 and change the oil once a year. Last year I put about 7,000 miles on the oil. The filter is probably as important as the lubricant. Don't use discount brand filters ? there is a real difference in quality here. The original Purflux, or Purolator, Bosch, Wix, or NAPA Gold is best. I personally do not like Fram. I use NAPA Gold 1085 (a cross with the Purolator L14670) because it is a large filter (I have the 45 degree elbow on the oil sender) and I like the larger filter capacity. Harold McElraft - 3354