Motor Oil 101. Before my real estate career began, I worked as a manufacturers' representative, selling automotive service equipment to dealerships, repair centers, tire stores, quick lube centers, etc. Some of the machines I sold were provided to those types of businesses at no charge by their bulk motor oil distributors, whereby a retail service center signed a five-year contract to buy all of their motor oil, transmission fluid, antifreeze/coolant, brake fluid, etc., etc. and in exchange for the commitment, were provided a package of service equipment that "dispensed" those fluid/chemical products. As a result, I got to work in the field demonstrating and training the use of the equipment nationally and regionally, with chemists who worked for the leading oil companies in the U.S., including Valvoline, where I garnered much of the technical/chemical knowledge I'm sharing with you now. These chemists taught me A LOT about oil, additives, detergents, friction modifiers, viscosities/liquified rubber and more.
Kirkland Motor Oil from Costco is re-packaged Mobil 1 synthetic motor oil. It's decent quality, lower end "synthetic" motor oil. A number of brands out there are re-packaged product manufactured by another company. As an example, Castrol is what in the oil industry is referred to as a "net packager," meaning that their brand is manufactured for them by another oil company, as is the case for Castrol. If you buy Castrol Syntec synthetic oil, you're getting Mobil 1 in a Castrol package. To further muddy the water, different standards apply on different continents/in different countries. There are five base stocks derived from "dinosaur oil." Group I base stock is your "regular," non-synthetic motor oil, which is being used less and less. Most auto manufacturers require, as a minimum, a "synthetic blend" motor oil, i.e. a Group II base stock. In some brands on the North Amercian continent, if a manufacturer of motor oil uses a Group II base stock with synthetic additives, detergents, etc,, it can be referred to/called synthetic oil...not to be confused with fully-synthetic motor oil...which is made with a Group III base stock. In Europe, an oil manufacturer/packager cannot call an oil synthetic with a Group II base stock, regardless of the additive package. Only Group III - Group V base stock oils can be called synthetic. For that reason, as an example, with Porsche, to keep your powertrain warranty requirement intact, you must use the euro-spec type of, for instance, Castrol motor oil...as the U.S.-spec equivalent is not deemed "good enough quality." At this point, you probably have figured out that Group I base stock is "the cheapest stuff," and Group V base stock is the "best stuff made." In a nutshell, more processing/refinement of the oil is the difference as you go up in grade (base stock). More hydrocarbons removed, more re-engineering/purification of the base stock, more polyolefins.
Ultimately, what you choose to use in your vehicles, if you have the basic knowledge and understand the basic product differences, is in my mind, a cost-benefit analysis based on 1) how long you typically keep your vehicles and 2) how hard you work your vehicle...towing or not, operating in consistently higher temperatures or consistently colder temperatures, are the key determinants of whether you will get the extra value of the extra cost of better oil. Growing up, my father changed cars about every nine months. He'd buy from the first dealer shipment of the newest model year, and it was replaced with a different vehicle by the time it had 8,000 - 9,000 miles on it. There was no return on investment in spending more for higher quality oil. I do just the opposite...I buy exactly what I want, brand new, and drive it for years, somewhere between 240,000 - 300,000 miles. I get to see the benefits of running higher-quality oil as a result. Our daughter, a high school senior, is driving what was her mother's 2008 Infiniti G-35 bought brand new with 6 miles on the odometer in March of 2008. It now has 208,000+ miles on it. The Nissan 3.5 liter VQ V-6 engine in the G-35, a great engine overall, is known to consume a lot of oil as it gets many miles on it, and the factory-fill motor oil and transmission fluid (also known to be rock-solid) was a non-synthetic, standard, Group I base stock oil in 2008. By the time you'd reach 150,000 or so on the odometer, having used regular (non-synthetic blend, non-fully-synthetic) motor oil for maintenance, it was common for a quart of oil to "disappear" every 800 miles or so. When our G-35 was new, I dropped the factory-fill oil at 3,000 miles on the odometer, and refilled with Royal Purple Fully-Synthetic motor oil (which has been purchased in recent years and is now a Calumet brand). I do oil changes with Royal Purple at 7,500 mile intervals. On the oil change cycle when the car was nine months old and there were 10,500 miles on the odometer, 1/2 quart of oil disappeared off the oil stick in that first 7,500 mile oil change cycle. Now, almost fifteen years later, it uses 1 full quart of oil during a 7,500 mile oil change interval. We lived previously in North Carolina when we bought the car, and since mid-2013, we've lived in Florida. Vehicles don't rust/get eaten up by road salt and calcium chloride down south. The replacement for the car, which our daughter loves, is likely to happen if/when she gets bored with it, or it is involved in a collision/accident with air bag deployment, which would make the car a total loss for insurance purposes. As a used car, it was worth about $6,000 years ago at 150,000 miles, and today with 208,000 miles, it's still worth about $6,000.
Obviously my go-to brand of fully-synthetic motor oil I use in all of our vehicles, as I have for twenty-six years, is Royal Purple. Today I can buy it at Walmart. When I first started buying it, I had to order it from Nichols Performance in Eastern Tennessee, a warehouse distribution company that sells primarily racing car parts. The API certified oil is manufactured with a Group IV base stock. If your powertrain warranty has expired, and you want to go next level with performance, their HP series oil, which has among other things in the formulation, extra zinc for the ultimate in valvetrain protection, is manufactured with a Group V base stock. I have seen a new Chevrolet V-8 crate motor on a dyno broken in with regular, Group I base stock oil. The oil was then drained, and it was refilled with Royal Purple HP Group V base stock fully-synthetic motor oil, started and run on the dyno again. The engine produced an extra 20 horsepower with the Royal Purple installed. By the way, a 5-quart container of the API spec GF-5 Royal Purple sells at retail for somewhere between $37 and $40 depending on whether you buy it at Walmart or one of the chain auto parts stores.
The competition for Royal Purple is Amsoil, with very limited distribution channels by design, and at a retail price that I personally just cannot justify...but it is manufactured with a Group V base stock.
These days I don't do a lot of the maintenance I used to do myself. My 2020 Ascent Touring gets serviced at the local Subaru dealership where I bought it, and I bring in a 5-quart container of Royal Purple with me for the lube tech to install when I'm there for service. I pay for the labor and the oil filter from the service department. I've never received any push-back from staff about providing the premium oil I want to use in my vehicle.
