I just registered, and this is my first post. First of all, I think you're doing a great job, I'm learning a lot, already. Here are some questions I have: I have a 1997 T-bird, 4.6L V8, and it just reached 80,000 miles. It has no oil leaks/oil burning etc. Since buying it at 71,000 miles, I've tried several kinds of regular oil(Motorcraft 10w-40, Valvoline Durablend 10/30-this was not good, somehow, and then Pennzoil High mile-10w/40) in it, but I'm technically not an expert to decide what's best for my car. However, I ALWAYS use Motorcraft Filters. The previous owner ran Pennzoil 10/40 in it, he says. With the Bird reaching 80,000 miles, I wanted to go synthetic, and now I have Pennzoil 10w-30 in it. After about 150 miles, I see that the oil level is good, no visible leaks, and the oil is very clear. So, 1) Have I made a good choice? Which other choices are there, which could be better? should I just use a higher mileage oil like Pennzoil HM or Valvoline? 2) Is it bad to turn to synthetics at this mileage? can I do any harm by running synthetics(leaks, etc.)? should I check the oil more often? Can I go back to regular? 3) The recommended oil is a 5w-30, is 10w-30 or 40 too thick? (I live in Tennessee, drive about 40 miles a day at an average of 65 mph(4 times a week), do not race or drive hard, change oil/filter every 3K, use Motorcraft filters, and want to keep the Bird as long as I can) 4) Which oils would you recommend? regular or synthetic at this mileage? (which brands for regular and synthetic?) 5) are there synthetic 10w-40 oils? Do I need it? Can it harm the engine?(too thick, etc.) I know it's a lot of questions, but as I said, I'm not an expert...I would much appreciate your feedback/info/answers to my questions. Thanks again, and keep up the good work.