Chris sells auto parts through his store, Beachside Auto Parts. He also dispels automotive myths on his TikTok (@ChrisFromBeachside) with the motto “stop guessing.” Here are three of the big ones, and my take on each.

Myth 1 – Premium gasoline

“Unless your engine requires premium gas, don’t waste your money. You’re not getting better performance, better mileage, or cleaner combustion.” I agree—if your gas cap says “Premium Only,” don’t skimp out.

Chris adds that premium gasoline is “not higher quality.” It’s true that higher-octane gas doesn’t contain any extra explosive energy. So what does a higher octane rating mean? Higher-octane fuels ignite more predictably than lower-rated fuels, which means they prevent engine knocking in the rare engines that run higher compression ratios. On lower-octane fuel, these engines will “knock” or “ping,” which can damage them.

What does this mean for you with a regular engine? It may be worth running one tank of premium gasoline through your car to see if it helps mpg. Some modern engines will run with higher compression if they detect premium gas, and the result may be a net cost savings. But if you don’t immediately notice an mpg boost, and your car is safe for regular gas, don’t bother with premium.

Myth 2 – Synthetic oil makes old engines leak

Chris argues that “Modern synthetic oils are 100% safe in older engines. In fact, they usually protect better, especially in cold starts, heat, and stop-and-go driving.”

I completely agree, but the more common myth is that modern synthetic oils make old engines leak. Chris argues, “Synthetics won’t make your engine leak. If it leaks with this, it was going to anyway.”

As with many myths, this one contains a sliver of truth. If you have an old car that is already leaking oil, swapping to synthetic will probably speed up that leak. Worse yet, you probably shouldn’t swap back to conventional oil after you’ve begun using synthetic in your old engine. But the good news is that synthetic is probably better than conventional oil in every way—if your old engine isn’t already leaking.

Myth 3 – A/C uses tons of extra gasoline

Chris called out the myth that you should shut off your A/C and roll down your windows to save gasoline. “Yes, AC uses a little gas, but driving with your windows down at highway speeds destroys your aerodynamics and hurts your miles per gallon even more. If you’re sweating to save half a mile per gallon, it’s not worth it.”

In my experience, this is often true. But again, if you’re curious, you can try running a test with your car during your next road trip. Run a full tank of gas on the interstate with the windows cracked and A/C off. Track your mpg. Then for the next tank, put your windows up, turn that A/C on, and see how your mpg changes.

Chris warns that these are “three car myths that people still believe but shouldn’t. You’ve probably heard these before, from your uncle, your mechanic, or some guy on Facebook, and every one of them is wrong.” I’ll add that you shouldn’t just trust some guy on Facebook. But it’s never a bad idea to test myths yourself. It’s a great way to get to know your car better for yourself.

MotorBiscuit has reached out to @ChrisFromBeachside on TikTok for comment. You can see his original video embedded below: