The 5W-30 is best for cold winters. Reason being as the cold air hits the oil-pan, it starts to mildly gum up the oil in the oil pan. When you do a cold start, the oil viscocity is real low when the oil is like this and gets better once the car hits operating temps. By putting a lighter weight oil in the car, you increase the oil viscocity in colder temperatures.
For the most part, 10w-30 will suffice on older stangs as these cars have low compression engines. The 5w-30 and 5w-50 are for the higher compression engines found in Imports with 4-cylinders trying to max out 200 hp at 5000 RPM's.
I guess if you're finding your car is burning a lot of oil, I'd use the 10w-30 in the winter and in the summer I'd switch to 10w-40.
Myself, in my 1990 5.0 I've been using 10w-30 Valvoline Max Life. It's a conventional/synthetic oil blend. It offers some benefits that synthetics use like treating the old dry seals while offering the same kind of performance found in your basic conventional oils without going 100% synthetic. I have no leaking issues of any kind and have not had to "top-up" between oil changes
My engine maintains a steady 51 psi at speeds of 120km/hr. At idle I'm between 25-30 psi.
Only warning I have for you is to stay away from Penzoil. I've heard of stories that 302's sludge up on that stuff.
Motorcraft is ok, but I think you're over paying for the same quart you'd get from Castrol GX.
I continue to use Motorcraft oil filters though. I've been tempted to use the Valvoline Max Life oil filters which are made by Purolator. The word on Purolator is that in the beginning they are really effective, however, due to the pleats being so close to each other, may not decontaminate older oil as quickly as if they were new.
whats the best to go with?
