Busted: 10 of the Most Common Car Care Myths

A lot of falsehoods get passed down from generation to generation. Take, for example, the idea that chicken soup will help cure a cold or that “the hair of the dog” will remedy a hangover (anyone who’s had one too many libations knows that doesn’t work).

If you’ve been driving long enough, you’ve also undoubtedly heard many car care myths, some of which you might not even be aware of are untrue. Now’s the time to set the record straight by separating fact from fiction so that you don’t waste time and money following automotive-related untruths.

10 Common Car Care Myths You Should be Aware Of

Thanks to the internet, there’s more information (and misinformation) available than ever before when it comes to car care. In fact, these days, it’s nearly impossible for a layperson to sift through the nonsense to determine what’s true and what’s not.

Following bad car care advice can be an extremely frustrating waste of resources. Let’s debunk some of the most common automotive myths so that you can make an informed decision about what’s best for your vehicle.

1. Premium Fuel is Always Better for Your Car

Many people believe that premium fuel is higher quality than regular gasoline when, in reality, premium just has a higher octane rating (resistance to spark knock or detonation). While premium provides advantages in a high-compression performance engine, there are zero benefits if your car is designed to run on regular gasoline.

That means you’re wasting money putting premium fuel into your car if the owner’s manual recommends regular. What’s more, in instances where premium fuel is recommended (but not required), you can almost always get away with using mid-grade or regular fuel, at least in a modern car.

Modern vehicles (those built within the last 30 years or so) have engine management systems that will retard ignition timing to prevent the detonation that might otherwise occur when using a lower-grade fuel in place of premium. The downside is that the retarded ignition timing reduces fuel economy and engine performance. 

In the end, the best practice is to always use the grade of fuel that’s recommended for your particular application.

2. Switching Back and Forth Between Synthetic and Regular Oil Can Ruin Your Engine

There’s a common misconception that once you switch to synthetic engine oil you can never go back to conventional (or vice versa). But actually, switching back and forth between the two types of oil is just fine, as long as you stick with the correct viscosity.

Before you switch back from synthetic to conventional, however, you might want to consider the superior performance and protection that synthetic offers. If you want the best for your car, it’s usually smart to stick with synthetic for the long haul.

3. A Poorly Running Car “Just Needs a Tune-up”

It’s not uncommon for classified ads to claim that a poorly running used car “just needs a tune-up”. While that might have been the case in the 1960s, when twisting a couple of screws on a carburetor could improve engine performance, there really isn’t such a thing as a tune-up on today’s vehicles.

Sure, there are still spark plugs to replace, but that’s about the extent of a modern tune-up. Plus, because today’s spark plugs often last more than 100,000 miles, worn-out plugs don’t lead to engine performance problems as often as they did in the past.

Truth be told, anything from a faulty sensor to an internal engine mechanical problem could cause a modern vehicle to run poorly. So, if you’re in the market for a used car, be sure to steer clear of anything that “just needs a tune-up”.

4. Diagnostic Trouble Codes Tell You Exactly What’s Wrong with a Car

When your car’s check engine light turns on, the engine computer stores one or more corresponding diagnostic trouble codes (DTCs) in its memory at the same time. Those code(s) can be retrieved using a scan tool or code reader. 

It’s a common belief that DTCs tell you exactly what’s wrong with a car. That’s not the case, though, as codes merely serve as a starting point for further troubleshooting.

For example, if your car’s computer has logged code P0131, which stands for “O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1), that doesn’t necessarily mean that the oxygen (O2) sensor is faulty and needs to be replaced.

Instead, the code only tells you that the computer has detected the oxygen sensor’s voltage signal has remained below a certain threshold for too long. The root cause of the issue could be anything from a faulty O2 sensor to a vacuum leak causing a lean running condition that forces the sensor signal low. It’s up to you (or your mechanic) to figure out the actual cause of the problem.

5. Tightening the Gas Cap Will Immediately Extinguish the Check Engine Light

While we’re on the subject of the check engine light and diagnostic trouble codes, it’s worth discussing another myth: The idea that tightening the gas cap will immediately turn off the check engine light.

It’s true that a loose gas cap can result in an evaporative emissions leak, which can trigger the check engine light. But there are also countless other reasons why the check engine light might be on, ranging from a loose wire somewhere to an internal engine concern.

Furthermore, even if the gas cap is indeed loose, tightening it will not extinguish the check engine light immediately. To turn the light off, you must either clear the codes with a code reader or wait for the engine computer to deem the problem is fixed, which can take a really long time.

6. You Should Warm Your Engine Up for Several Minutes in the Winter 

The average American believes that they should let their vehicle idle for more than five minutesbefore driving in cold temperatures. While that may have been true in the past—when vehicles relied on carbureted fuel systems that would stall out when cold—it’s not true with modern fuel-injected engines. These days, letting your car idle for more than 30 seconds does nothing for the engine, but it does waste fuel and increases harmful tailpipe emissions.

Of course, if it’s frigid outside, you might want to let the engine warm up so that the heater and defroster are working well before you take off.

7. A Misfire Means Bad Spark Plugs

An engine misfire is a problem that results from incomplete (or zero) combustion inside one or more of the engine’s cylinders. The issue can trigger the check engine light and cause your car to run rough, stumble, and lack power.

Since the problem is called a “misfire”, many people falsely believe that the spark plugs must be to blame. After all, the plugs are what “fire” to ignite the air-fuel mixture inside of the engine.

Indeed, it’s true that worn-out spark plugs can cause a misfire, but there are many other possibilities, as well. Your car’s engine needs three primary ingredients to run well: adequate spark, a precise air-fuel mixture, and good mechanical compression. If one or more of those elements is missing (due to a fuel delivery problem, engine mechanical failure, etc.), the engine will misfire.

8. Engine Overheating is No Big Deal 

In the movies, engine overheating is portrayed as a normal occurrence that can easily be cured by adding a bit of water to the radiator. In real life, however, overheating is not normal—it means there’s something seriously wrong with your car’s cooling system. 

Overheating can also quickly lead to internal engine damage, so you should never ignore the temperature gauge climbing above the normal operating range. Instead, pull over immediately, shut off the engine, and have the vehicle towed to your location of choice for repair. 

9. It’s Normal to Have to Top Off Coolant and Other Fluids

Many drivers believe that having to occasionally top off fluids, such as engine coolant and transmission oil, is a normal part of car care. But the truth is, it’s not normal because a car does not “burn” any fluids except for gasoline and possibly a small amount of engine oil (washer fluid also gets used up eventually). If you’re having to top off any of the other fluids, there’s a leak somewhere that you’ll want to address right away.

10. Any Car Problem Can Be Solved with YouTube

Perhaps one of the most prevalent (and troubling) myths is that anyone can diagnose and repair any car problem simply by following a YouTube video. While YouTube is a valuable resource, there is a lot of misinformation that you might stumble upon. What’s more, a repair video that applies to one vehicle might not pertain to the model you’re trying to fix. 

That’s why if you’re serious about DIY auto repair, it’s important to invest in a repair manual or access to a repair database so that you have quality service information for your application. Anything you find on YouTube can be used as a supplement to the genuine repair information you have on hand.  

Don’t Believe Everything You Hear (or Read Online)

Perhaps the most important piece of advice is not to believe everything you hear (or read online). Instead, do your own research or ask a professional for car care advice. Doing your homework will help you avoid falling for myths that can lead you down the wrong path, costing both time and money.