Hello, When we were running the 1958 Impala, the only oil grade we used was 30wt Valvoline. In 1960, we, first used cans of 30 wt. in the Flathead, but at the rate of usage of oil, it got expensive real fast. So, we turned to gallon containers of 30 wt. recycled oil. That weird oil was recommended by our local Flathead mechanic. His experience had no chance against the 1940 Ford Sedan Delivery Flathead’s oil usage. It was a mystery. So, he recommended the recycled oil. Maybe he was smarter as the recycled oil was thinner and still did the fine job of lubricating the Flathead on those long drives up and down the coast. https://www.jalopyjournal.com/forum/threads/teenage-hot-rodders-cheap-tricks-in-the-60s.1081062/page-5#post-12327514 The recycled oil being thinner was supplemented by the random STP additive. We also used the STP additive in the 348 and when we built the 40 Willys coupe with the 283, then the 292 671 SBC motors, we used 30 WT. Valvoline and STP again. At the time, all of the top racers were using either Wynn’s Friction Proofing additive or the STP brand of additive to their engine oil. This is/was home away from home for a gallon+ of reclaimed/recycled oil. Jump up to the time when automotive articles were beginning to praise the double weight oils, made changes for all of us. It seemed logical to use a 10 wt / 30 wt for the motors. Then the advantage of some high powered motors called for 20/50 wt oils. It was a merry-go-round of choices for every motor in domestic and European cars. Jnaki In our 327 from our 2nd 40 Ford Sedan Delivery, we still used 30wt Valvoline. But, my wife’s high performance car required 20-50wt. oils as recommended by the factory and her mechanic. Today, people have so many choices that it is daunting. The rate of oil change all depends on your upbringing and work history. But, for the most part, the multi grades seem to be the oil of choice. My neighbor has not used anything else other than Mobil-1 since it came out. Maybe, it is because he used to work for Mobil Oil. He probably owns plenty of company stock shares... Ha!