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Thanks for the info. Is adding a Zinc supplement beneficial?

Originally Posted By: old1 By QS 10w30 with added zinc, do you mean QS Defy ?? If so, from what I have read here and elsewhere that is what I have switched my old (1950-1965-1980) vehicles to now that I have used my stash of SL rated oils. I'm not sure about the Defy... It come in a 5qt red...

Originally Posted By: 440Magnum If those engines have stock cams and lifters, then you really don't have much to worry about. You *could* use the latest SN-rated 5w30 without concern at all. I would pick by grade first, then by additive package. Any of the "high mileage" oils are a good pick...

Hi everyone. I've searched prior to posting with no luck, just confused. I have two older GM V8 powered engine cars. 1975 Pontiac GrandVille, 455 1980 Cadillac CDV. 368 I'm lost as to what spec oil I NEED. These cars sit in an unheated garage in NC, mild climate. I used the QS 10w-30 with added...