 1990 Mustang 5.0 supercharged what oil to use?
I just got a supercharged 1990 mustang 5.0. It has 145,000mi at the moment and I was looking at the window sticker from the last oil change and noticed it had been serviced with 20W-50. Is this a good weight for a supercharged car or sould I use 10W-40 or 30? I also heard if a heavier weight oil has been used for a long time it isn't good to switch back to a lesser weight is there any truth to that? Thanks in advance
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