Hi Guys/Gals. I have a very stock 1974 slant six engine in my 1974 Duster. Stock motor and heads, mix of town and highway driving. I change the oil about every 2500 miles. I use NAPA store brand 10W-40 oil in it year round, altho I don't drive it outside in our Minnesota winters. I just warm it up in my garage. The NAPA store oil that I buy is API grade SP, repackaged Valvoline oil (at half the price - $11.99 for a five quart jug). This stuff is way better than what we had back in the day when my car was new. In any case, does my car need zinc additive? I kinda thought that by 1974, they didn't need zinc rich oil any more. So I don't use racing oil with zinc, nor do I add zinc at my oil/filter changes. What do you think? Slant six Dan, if you're out there, please weigh in. Thanks all!
