Originally Posted By: Mark_Hone
Hello: New member here (long time lurker) and I have a question. I have a 1966 289 4bbl Mustang auto. I store it in the winter and drive it in the summer. I put about 5000 miles during the summer and the car runs like a dream. The compression is not bad (120ish), the bearings might not be as tight as they once were, the lifters and valve seem ok, a couple of small oil leaks ( rear bearing a couple of drops a week), and burns about 1 quart over the summer. It's just an old car, great shape but not a trailer queen. I have been using Mobil1 10w30 for years (the car called for 10w30 back in /66) and a Ford oil filter. I put new oil in at the start of the driving season. Question: do you think I should stick with the thinner oil (oil pressure is about 5-10lbs when hot) or change to a heavier oil (20w50). I don't understand the theory of thinner oil flow vs heavier oil filling up any spaces between bearings, lifters & pistons. Or maybe I am just over thinking the whole subject. The car has 100,000+ miles and I drive city and highway speeds. Thanks in advance. Mark Hone.
Welcome to the forums!
Considering that you just drive the car normally (based on your description above) and don't drive it in the winter, any 30 or 40 grade oil would technically work well. Since the car is not new and, as you pointed out, it may have some lower end wear, a 40 grade is not a bad thing. I personally wouldn't jump all the way to a 50 grade, but certainly any synthetic 40 grade of your choice would be fine.
Don't get too hung up on the first number (especially since its not winter driven). When purchasing a synthetic oil, you don't have to worry as much about shear stability in most normal street-driven applications. M1 0W40, Castrol Edge 0W40, any synthetic 5W40 or synthetic 10W40 will perform just fine for you. If you did want to get into a conventional oil, then it would be best to purchase an HD 15W40 product.
Also, I would do the oil change right at the end of the driving season, just prior to storage, so that the car is stored with new, uncontaminated oil. In the spring, you just take it out and drive as normal. Change again just prior to storage. There is likely some fuel dilution in the oil and storing it that way is less than ideal.
Hope this helps and enjoy the ride.
