By Lake Speed, Jr. – Certified Lubrication Specialist at Driven Racing Oil
If you want to start an argument among car guys just bring up the topic of motor oil. Near religious fervor accompanies these “discussions,” but there never seems to be a resolution to the eternal question of “which is the best oil?” Each person’s favorite brand seems to have provided “good luck” when it comes to lubrication. But how can this be?
The reason for the lack of a clear answer is two-fold. First, there is no “best oil.” The idea of a one-size-fits-all motor oil is a myth. All oils are application-specific in their formulation. “The best” diesel motor oil is still a terrible two-stroke oil.
Second, it is the wrong question to ask. As just described, oils are application-specific by nature. What you really need to determine is which oil best suits your application.
Simply put, all oils lubricate. The most important question then is, “for how long and under what conditions can they do so?”
A perfect example is Castor bean oil. Castor oil has great lubricity, but it does not stand up to temperature extremes. As a result, it is an excellent two-stroke oil, but it would be a terrible diesel oil.
Another modern example is automatic transmission fluid. Each major transmission manufacturer now has specific viscosity and frictional requirements for their transmissions, and all of these specifications are impossible to meet with a single fluid.
But you are thinking that you’ve seen (maybe even used) Multi-Vehicle ATF and people have had “good luck” with it. Again, how can this be?
What you need to remember here is that you have to determine how long the oil will lubricate and under what conditions.
A Multi-Vehicle ATF may work fine in a mild climate under mild driving conditions, but will it still work towing a trailer in Arizona?
Harsh environments and severe service demand more of the lubricant, and an automatic transmission requires different properties than a diesel engine. So while a diesel motor oil can lubricate an automatic transmission, the question remains – for how long and under what conditions? Obviously a diesel motor oil in an automatic transmission is a disaster waiting to happen. The viscosity is all wrong, so the transmission likely would not function properly at low temperatures. Purpose-built lubricants are designed to handle severe service in specific applications, especially in extreme conditions.
Please note that “extreme conditions” do not always mean towing a trailer through Death Valley, CA. In fact, sometimes grandma’s grocery getter in Green Bay is more “extreme” in terms of taxing the oil and the potential damage to the engine. Short trip driving can cause way more sludge than operating in desert environments, especially in cold climates where the engine oil struggles to get over 200°F.
That is where motor oils can get confusing. While a racing oil sounds like an oil that is perfect for extreme conditions, it is a bad choice for a daily driver. Using a racing oil in a daily-driven street car is not just overkill; it is just the wrong type of lubricant for a daily driver. Even if your daily driver is a pushrod V8, the racing oil NASCAR teams use in their pushrod V8 engines is not designed for the rigors of daily driving.
NASCAR engines run high engine speeds and high temperatures, both of which require generous amounts of exotic friction modifiers. While this chemistry is perfect for a race engine, these same friction modifiers that reduce wear and oil temperatures at 9,000 RPM also clog emissions system equipment in your daily driver at 3,000 RPM.
The examples are nearly endless, but the point is still the same. When you choose an oil for your transmission, motor or lawn mower, think about the application before you think about the brand. Once you think about what your application requires, you can then find oils that meet those requirements and are the correct viscosity for the application. Finally, you can choose a brand you trust to deliver the right chemistry in the right viscosity.
A great example of this process is what I do with my wife’s mini-van. To select the right oil I look at the owner’s manual and find what spec is required. In this case it is API SN/GF-5.
Next I look up the recommended viscosity. Her owner’s manual lists 0W-20 as the recommended viscosity grade, so now I choose a brand I trust to deliver API SN/GF-5 performance in a 0W-20 viscosity grade every time I open a quart.
I do the same thing when I select an oil for my four-stroke racing engine. I already know I need a racing spec oil instead of an API spec oil, so the next thing to determine is which viscosity grade racing oil I should use. Based on the operating oil temperature and bearing oil clearances, I see that I need to be running a 0W-20 viscosity.
While both engines ended up running a 0W-20 viscosity grade, the oils needed for each are chemically very different. However each lubricant is the best fit for its specific application. As a result, my wife gets good gas mileage and my race motor makes more horsepower.