If you pop your car’s hood and look around a bit, you’ll likely find some text or even a brand logo near the oil fill cap. The message might indicate which oil brand you should run in the engine. For instance, the oil cap on my Range Rover says, “Castrol recommended.” In reality, my car’s engine has exactly zero awareness of Castrol…or any specific brand, for that matter.

When it comes to engine oil, a few things actually do matter. The main keys are weight and formulation. Weight is the number you’ll find in the car’s manual and on bottles of engine oil. Modern cars use multigrade oil, meaning you’ll see two numbers on their spec. For example, 5W-30. The numbers indicate the thickness of the oil when either cold or hot. The number before the “W” is its viscosity, or flow rate, cold. The number after the “W” is the viscosity at 210 degrees Fahrenheit. 

Traditionally, heavy-use industrial engine oils have a single number, or what’s called “straight” oil. It’s also called “crude” oil. Modern car oils achieve multigrade status through additives.

Automakers design their engines separately from each other. Thus, they have varying clearances and performance specs that oil must properly account for. As such, different brands and models will call for different weights and formulations.

For example, most modern Toyotas use 0W-20 full synthetic. Others might use a 5W-30 synthetic blend.

This is all to say that your car wouldn’t know if you’re running Castrol or Mobil if its life depended on it. What it would know – and get sick or even die over – is if you ran a lower-performance oil than its design allows for.

In fact, brand recommendations are simply a marketing strategy stemming from a handshake between the oil company and the automaker. Moreover, most branded oils come from just a few oil suppliers worldwide. So, you’re mostly paying for the logo stamped on the bottle.

Most independent shops buy oil in bulk drums, which is why smaller operations might be cheaper than the dealer. Many automakers have agreements with certain brands and are bound to those logos. If you want to save money on your oil changes, just make sure the weight and formula are right. You can look up any “alternate” brand’s approved model uses right on the back label or on a spec sheet available online. Don’t worry so much about the brand name.

Finally, after making sure you’re running the correct oil weight and formula for your engine, the single best maintenance you can perform to prolong your engine’s life is to change the oil regularly. I do this more often than the manufacturer suggests. I don’t care how fancy the oil additives get; once a year isn’t often enough to prevent sludge and crud buildup over time.