I had a 1971 Ford Maverick with a 250 cubic inch 6 cylinder engine. I used Sunoco 10W-40 oil and after I had the valve stem seals replaced, I got about 1000 miles per quart of oil. One day, I saw Valvoline on sale for 25 cents a quart in the 10W-40 viscosity. I couldn’t resist, and gave the Valvoline a shot. The oil consumption dropped to a quart every 1250 miles. I bought an Oldsmobile Cutlass with a 260 V-8 brand new in 1978. In the 33 years and 240,000 miles I owned the car, I probably used every brand of 10W-30 oil in the car. It never used a drop between changes. I found Citgo oil on sale once and with the mail-in rebate, the oil was 0 cents per quart (free motor oil)
I now have a 2011 Toyota Sienna. The dealer’s service department used Valvoline so with the free oil changes I had for two years after the purchase, Valvoline went into the crankcase. Now that my independent shop services the Sienna, it still gets Valvoline. In the case of my Sienna, the oil required is synthetic 0W-20.
I learned that the brand of oil doesn’t matter from a U-Haul dealer where I rented a truck. At each gas stop, the oil was to be checked. I was told what viscosity to use. When I asked about the brand, the dealer said that oils have to be compatible if the oil refiners want to sell oil to the government which they all do. The important thing is to not let the engine get low on oil. I was told to keep the receipt for any oil that was added and it would be taken off the bill. That was a good thing. I rented the truck on a return basis and drove 125 miles to our apartment when we went to graduate school. We unloaded the truck and proceeded to a cut rate gas station to fill the tank. When the oil was checked, it was 2 quarts low, so I had 2 quarts put in the truck. When I returned the truck, the U-Haul dealer filled the tank and checked the oil again. It was 2 quarts low. I gave him my receipt for the oil which he honored, and then looked at me and grinned and said, “The truck uses a little oil”.