I know a lot about cars, you know a lot about cars, but how many old myths have you heard and believed without realizing they weren’t true? It’s less common now thanks to the power of the internet giving all of us loads of information from multiple sources, but even with that, there are lots of things floating around that a lot of car guys and gals still believe to this day.
So, I took it upon myself to dig into as many of these obscure myths as possible. Some of them are related to fueling, legalities, electronics, and more. Before we get into it, make sure to drop a comment down below, letting me know what car myths you believed for a long time until you found out it was a lie and your mind was blown.
#1 Turning on the A/C Makes the Car Slower
The very first thing I want to get into is something I still see in meme form all the time on Instagram and random Facebook pages, and that’s the idea that turning off your A/C will make your car faster, especially in underpowered cars where any change in the engine’s power output is very noticeable. But the thing is, turning off your A/C won’t affect how much peak power your engine outputs.
I know it might not be true, but stick with me for a second. Your A/C compressor is driven by the accessory belt of your engine. Therefore, it takes power away from the engine in order to drive the compressor. With that in mind, you’d think that taking power from the engine to drive the A/C compressor would make your car slower, but automotive manufacturers thought this through long ago and came up with a simple solution: disengage the A/C compressor at full throttle.
I can’t verify this is the case for 100% of modern cars, but it’s safe to say nearly all modern cars will disengage the A/C compressor at full throttle. If you’re asking the engine for all the power it has, then it should deliver that, and temporarily disabling something like the A/C compressor simply makes sense if you want the engine to deliver full power.
Another thing to note is that modern A/C compressors are ultra-efficient as compared to older systems, so the system on a 2009 truck will use significantly less engine power as compared to something from 1989, for example.
So yes, your 1990s sh*tbox does feel slower when the A/C is on, and it does, in fact, make less power at part throttle with the A/C on, but when it comes time to go full throttle, it makes zero difference if the A/C is on or not, because the compressor should disengage to allow the engine to deliver its maximum power output.
#2 3k Mile Oil Changes
The next myth, which has actually died out, for the most part, is the idea that you HAVE to change your oil every 3,000 miles when in reality, modern oils break down much slower than they used to, and because of that, 3,000 miles is really overkill unless you’re talking about a high-performance application where you’ll likely see more metal shaving in your oil from extended track use.
I do want to say, though, that this isn’t a black and white thing. Even things such as the fuel you use can change this, as different fuels can break down your oil faster than others, but in the majority of applications, there’s nothing wrong with pushing your oil changes out to 5,000 miles, 10,000 miles, or even more in some cases.
Seriously, if you don’t believe me, run one 10,000 mile oil interval on your car and send your oil in for analysis, it’ll likely come back that the oil was still providing excellent lubrication, cleaning, and the oil contained acceptable levels of metal shavings. I’ve seen it happen firsthand, even in performance applications such as a Ford Focus ST.
That being said, if you’re in a really old clapped-out car, it’s probably better to stay on the safe side and stick with slightly more frequent oil changes, but for anything modern using a modern oil, 5,000 and 10,000 mile oil changes are perfectly acceptable. And before you go running to the comments about lube techs saying this or that or your mechanic saying this or that, remember that they’re making money off your oil changes, so they’re not going to be inclined to tell you to get your oil changed less often.
#3 Octane Ratings
The next myth I see all the time is that higher octane fuels produce more than lower octane fuels, and this partially the fault of fuel companies marketing it this way, but the truth is actually the direct opposite, lower octane fuels produce more power. Before you go running to the comments, just give me a second to explain this.
The octane rating itself is just a rating on the fuel’s combustion predictability and likelihood to pre-detonate, which is igniting from heat and pressure rather than the spark plug. More specifically, the octane rating is actually a measurement of the ratio between a fuel’s octane, which is a compound called iso-octane, and another compound called heptane.
So, in the case of 93 octane fuel, were looking at 93% iso-octane and 7% heptane, but the thing is, heptane is more chemically energetic than iso-octane, but it’s also less stable and predictable. With that in mind, a fuel containing more heptane will actually be chemically powerful than a fuel containing less heptane. Therefore, 91 octane is more chemically powerful than 93 octane and, as such, produces more power.
But, this is assuming were testing 91 vs 93, on the same engine, on the same day, in the same conditions, and with zero adjustments to ignition timing through the ECU. And, the measurable difference in terms of horsepower in this setting is very small, likely 1 to 2hp in a decently sized engine, so its nothing you’d even be able to feel.
With modern cars and engines, however, we have ECUs, and those ECUs get signals from knock sensors, so if your engine detects zero knock, it’ll try to advance your ignition timing a little bit until knock becomes present, then dial it back a little bit.
Since 93 octane is more stable than 91 octane, your ECU will be able to advance ignition timing more without running into pre-detonation, and therefore your ECU will adjust ignition timing and boost if applicable, to match the stability of the fuel you put in it, and because of that, a higher octane fuel will allow more ignition and boost to make more power if the ECU adjusts accordingly.
#3b Ethanol Makes More Power
And that actually takes me to a piggyback off of that myth, which is that ethanol fuel such as E85, that lots of people like to run in boosted cars, makes more power, and again this isn’t true for nearly the exact same reason, which is that ethanol is actually very low on energy density as compared to gasoline, but it’s much more stable, and therefore you can run more boost and more ignition timing to make more power, but the fuel itself isn’t the thing making more power.
In fact, the energy density difference between high ethanol content gas compared to low ethanol gas is so extreme that many boosted cars have to run larger injectors with more powerful fuel pumps to keep up with the demand because, with less energy density, you need more of the fuel itself to match standard gas.
#4 Placing your Battery on the Floor
Personally, this next myth of literally never heard of, but according to the internet, it’s something a lot of us were told at some point, and it’s flat out incorrect, and that’s the idea that placing your car battery on the floor will cause all the energy to leak out of it and ruin your battery.
And I will say, this actually used to be true back in the day, but with modern technology and modern batteries, it’s just not the case anymore. Batteries today are encased in plastic or hard rubber, which significantly reduces any energy waste, but batteries do naturally self-discharge over time, but this is due to an internal process, not the type of material on which the battery is sitting.
Before we had modern battery casings, energy could and did get drawn through the casing and to the floor, but thankfully this is no longer the case.
#5 Filling up in the Morning is Cheaper
Yet again, we’ve got another super weird myth that I’ve personally never heard of, but it seems as though a lot of you out there have, and that’s filling up your car with gas early in the morning because it’s cheaper. This idea revolves around the myth that ambient temperatures are cooler in the morning, so the gasoline is supposed to be denser because it’s also cooler.
In theory, this could actually be true, but there are a few things that make it a myth: one, the tank holding the gasoline underground isn’t all that sensitive to outside temperature fluctuations throughout the day, and the actual difference in gasoline density from say 60 degrees Fahrenheit to 50 degrees Fahrenheit is so small that there wouldn’t even be a measurable difference at the pump.
So while the science of this idea does actually work in theory, in reality, the temperature fluctuations of the gasoline at the pump are really small, and because of that, you’ll see no measurable difference, so sleep in because getting up early to get your gas a little bit cheaper is a myth.
#6 Exhaust Back Pressure
This next myth is something I’m not sure will actually ever be laid to rest because of how different engines and exhaust systems behave, but this myth is the idea that you need some amount of back pressure in your exhaust system for peak performance and that zero back pressure is not only bad for performance but also bad for your engine.
Right off the bat, though, this isn’t fully true, and a good example of this is Top Fuel cars, which have massive engines producing upwards of 11,000hp. These guys are concerned with making loads of power, so if back pressure was important to power output, why do high horsepower drag cars use open header exhaust systems?
I do think it’s worth noting, though, that excessively large of exhaust piping and/or a poorly designed exhaust system can reduce exhaust scavenging, which can result in a decrease in total flow and ultimately less power.
When an exhaust pulse comes through the exhaust system, it creates a low-pressure area behind it. With a good design, this low-pressure area can help pull the following exhaust pulses out. This is where the idea is that zero back pressure can reduce scavenging effectiveness, but this is really dependent on the application and the design of the exhaust system.
It’s certainly not a black-and-white myth, as there is some truth to back-pressure affecting exhaust scavenging effectiveness and the scavenging ultimately affecting the power output of the vehicle.
#7 Interior Light / Intersection Lane Change
The next two myths are actually something I believed for the longest time, and you probably did too, and that’s two laws: the first one being that you can’t have your interior dome lights on while driving, and the second one is that you can’t change lanes in an intersection. I want to preface this by saying where you live may have different laws, so check your local laws before trying these things.
The first one, though, I can’t even tell you how many times I needed to turn on the dome light as a kid, and my parents would tell me that it’s illegal and all these things, but uh yea, according to Arizona law, that’s not the case. I went basically my entire life thinking that was illegal, but that’s not the case.
I honestly think parents just tell their kids that it’s illegal to stop them from doing it, because the reflection of the windshield can actually make it hard to see where you’re driving.
The second one, changing lanes in an intersection, I heard that a long, long time ago as a kid in my friend’s mom’s car as we were going somewhere, and I just never thought anything of it until literally today when I asked my friends what their favorite car myths are and somebody mentioned changing lanes in an intersection, and yea, again, according to Arizona law there is nothing prohibiting lane changes in an intersection.
That being said, I still think it’s not a great idea since the lack of lane lines can make it hard to identify if a car is changing lanes, which can be pretty dangerous at an intersection where there are tons of cars, pedestrians, people trying to turn right, and more.
#8 Ethanol is Corrosive
The next myth I’ve seen and still hear to this day is that ethanol is corrosive as compared to gasoline and that it’ll tear apart your fuel system and destroy your lines, and on and on and on. And while there is some truth to the fact that when ethanol was added to gasoline at pretty much all pumps, making all gas effectively E10, it’s not necessarily the ethanol itself that caused issues.
In some applications, ethanol can corrode and dry out rubber and plastic gaskets, but that’s generally on older vehicles and not something we see on new cars, as manufacturers started using different materials in their gaskets to prevent this from happening.
The bigger issue is that ethanol attracts water, and when ethanol and water get together, you create a bacteria known as acetobacter, which can then excrete acetic acid, which is very corrosive, but this really only happens if your vehicle sits for extended periods, such as a motorcycle, a lawn mower, or the project car that’s been sitting on jack stands in your driveway for months on end.
So while ethanol isn’t great for older vehicles with older rubber gaskets and seals, up to E15 is approved for all vehicles 2001 and newer. So, plain and simple, low amounts of ethanol such as E10 or E15 are totally fine for newer vehicles, but what about something more performance-oriented such as E54 or E85? That’s where things can differ.
As you go up in ethanol content, it gets harder and harder to remove the water content completely, which can result in corrosion, but there are a few tricks to preventing this from happening, such as storing said ethanol-powered vehicle with a full tank.
So as far as ethanol being corrosive, this is partially true because of the water content, but for the most part, isn’t something to worry about. If you’re driving an older car, it is a good idea to replace your fuel parts with newer rubbers and materials that won’t die when exposed to ethanol fuel.
#9 LS is based on the Windsor
The next myth I hear that has always really annoyed me comes mostly from Ford guys specifically, who claim the GM LS and LT engines, which are the Gen III, Gen IV, and now Gen V small-block engines, are a rip-off of Ford Windsor and that GM had to copy Ford’s designed because they couldn’t design a good engine on their own and on and on and on.
A lot of this comes from guys who want everyone to think Ford is better than GM, and any shade they can throw at the LS and LT will somehow look the Coyote look better. Here’s the thing, with an overhead valve V8 engine, there are really not that many designs you can go with, and I will say that certain LS heads can, in fact, bolt-on to a small-block ford with almost no modifications, but just because they easily bolt-on doesn’t mean they work at all.
The valve orientation of the heads is different, the oil passages are different, the coolant passages are different, the valve stems are thinner and longer in length, and more. Are the port layouts and head bolt patterns similar? Sure. Is the deep skirt block with cross-bolted main caps reminiscent of the Ford Y-block? Yes.
Did they blatantly copy the Windsor engine? No. Does the LS have many similar features to the Windsor engine? Yes. That doesn’t mean they straight up copied it. If Ford found great ways to design the heads for flow and cooling, who is to say that GM didn’t do their own R&D and come to similar conclusions?
At the end of the day, there are only so many ways to design an overhead-valve V8 engine, so just because the LS has some similar features to the Windsor doesn’t make it a rip-off or that GM copied it.
And besides that, you’d be crazy to think manufacturers across the automotive landscape don’t spy on each other’s work and start the base of their R&D on another company’s work. This happens all across the automotive industry, from vehicle manufacturers to aftermarket parts manufacturers. There’s an old saying I’ve heard as a replacement for “research and development,” and that’s “ripoff and development.”
Is it plausible that GM started the development of the LS with tons of Ford parts that they thought worked well but could be even better? Definitely, in fact, I’d say that’s a likely conclusion, but don’t think Ford hasn’t done the same to GM or that it doesn’t happen to every company in every industry.
#10 Your Car is Actually Fast
The last myth is something you’ve probably heard from all your friends and your family, and you even perpetuate it yourself. This one hurts bad, and it’s something that we’re all guilty of believing, and that’s that you think your car is actually fast.