I put well over 100,000 miles (maybe closer to 200,000) on my old Mustang V6 using nothing but leftover miscellaneous bottles of engine oil I got from work. Car was cheap, didn't care much about it. They were all different viscosities, ranging from 5w30 to 20w50 and about everything in between, lots of 15w40. Different brands too, and different classifications (CJ, CJ4, MA, etc). Just whatever I had leftover from oil changes. Did it do any damage? Dunno. I sold it, odometer showed a little under 400,000 when it went to the new owner.
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