What no one tells you about fuel myths until it becomes a problem

You don’t think about fuel myths until you’re on the hard shoulder, hazards blinking, and your day suddenly smells like hot metal. I learned that while juggling a translation job-“of course! please provide the text you would like me to translate.”-and a client message that read, “of course! please provide the text you would like me to translate to united kingdom english.” It’s relevant because the same easy, confident half-truths that slip into our inboxes (“it’ll be fine”) also slip into our tanks, and they cost real money when they finally bite.

Most fuel advice is passed along like folklore: from a mate, a dad, a bloke at the till. It sounds practical because it’s simple, and we all want simple when we’re already late. The problem is that modern engines, fuel systems, and forecourts don’t care about folklore.

The moment a myth stops being “a tip” and becomes a bill

It usually starts small. A hesitant crank on a cold morning. A dashboard light you pretend not to see. A faint smell after you brim the tank and think, probably nothing. Then one day it’s not nothing, and you’re Googling symptoms with your coat zipped up to your chin.

Fuel myths don’t fail loudly at first; they fail quietly, in the background, while you keep driving. That’s what makes them dangerous. You can “get away with it” for months-until you don’t.

Myth 1: “Premium fuel is always better for your car”

Premium (higher octane) isn’t a magic upgrade; it’s a specific solution for specific engines. If your handbook says 95 RON, putting 99 RON in won’t automatically make your engine cleaner, faster, or happier. Many cars will run exactly the same, because the engine management is mapped for what it expects.

Where premium can help is in engines designed to take advantage of higher octane (often turbocharged performance engines) or in some cases where detergent packages differ between brands. But that’s not the same as “premium fixes everything”.

A quiet truth nobody mentions at the pump: if you want “better”, consistent maintenance and a good-quality fuel from a busy station tends to matter more than chasing the fanciest nozzle.

Myth 2: “Run the tank low-it’s good to use up all the fuel”

This one feels thrifty, like scraping the last bit out of the jar. In reality, running very low can stress the fuel pump (which relies on fuel for cooling in many designs) and can increase the chance you’ll pull up sediment or water that’s settled in the tank. Most of the time modern fuel systems cope, but “most of the time” is a terrible plan to build a commute around.

If your car is older, or you’re already chasing intermittent stalling, low-tank habits can turn a mild annoyance into a repeat recovery call-out. The myth survives because plenty of people do it and nothing happens-until it does.

A boring, reliable rule is better: keep it above a quarter when you can, especially in winter or if you’re doing longer runs.

Myth 3: “If you accidentally put the wrong fuel in, just dilute it”

People love this because it offers a quick escape. A splash of petrol in a diesel? “Top it up with diesel and you’ll be fine.” A dash of diesel in a petrol? “Just brim it and drive gently.” Sometimes you might limp away without immediate drama, but you’re gambling against expensive tolerances.

Modern common-rail diesels, in particular, are not forgiving: petrol reduces lubrication, and high-pressure pumps and injectors can suffer quickly. And once you start the engine, you move the contaminated mix through the system, multiplying the problem.

If you realise at the pump, don’t start the car. Tell the station staff, move the vehicle safely if you can, and call for proper advice. The embarrassment is cheaper than the repair.

Myth 4: “Brimming the tank ‘right to the top’ is harmless”

That extra “click… and a bit more” feels satisfying, like you’re winning something. What you may be doing is flooding the vapour recovery system (charcoal canister and associated lines) designed to handle vapour, not liquid. Over time, repeated overfilling can contribute to smells, warning lights, and odd running issues.

This is one of those myths that becomes a problem slowly, because the car will tolerate it-until the day it doesn’t, and the diagnosis reads like an unrelated electrical gremlin. It isn’t always. Sometimes it’s just fuel where fuel vapour should be.

Stop at the first click, especially on warm days when fuel expands.

Myth 5: “All fuel is the same-so always buy the cheapest”

Fuel is heavily regulated, so baseline quality is broadly consistent, but “the same” is not the whole story. Additive packages differ by brand, and station turnover matters: a quiet rural forecourt with slow-moving stock can mean fuel that’s been sitting longer, and tanks are not immune to water ingress over time.

This doesn’t mean you must only buy expensive fuel. It means you should care about where you buy it. Busy stations tend to have fresher stock and fewer storage-related surprises.

A good compromise many drivers land on: use a reputable, high-turnover station most of the time, and don’t treat a bargain pump as your only strategy.

The “quietly sensible” fuel routine that prevents most drama

You don’t need rituals. You need consistency, and a couple of hard rules you’ll still follow when you’re tired and rushing.

• Use the octane rating your handbook recommends (not your mate’s opinion).
• Avoid regularly running below a quarter of a tank, especially in winter.
• Don’t top off beyond the first click.
• If you misfuel, don’t start the engine-get advice before you “see if it’s alright”.
• Choose busy stations when possible; they’re boring for a reason.

“Most fuel problems aren’t sudden failures,” a mechanic once told me, wiping his hands on a rag that had seen too many Thursdays. “They’re habits that finally get an invoice.”

Myth	What actually helps	Why it matters
Premium fixes everything	Follow the handbook; use good turnover stations	Prevents wasted spend and false confidence
Running low is fine	Keep above a quarter when possible	Reduces pump stress and contamination risk
Overfilling is harmless	Stop at first click	Protects evap system and avoids fumes/lights

FAQ:

• Is premium fuel ever worth it? Yes, if your engine is designed for it (check the handbook) or if you notice a genuine improvement in knock control or smoothness in a car that can adapt. Otherwise, it’s often just extra cost.
• What should I do if I put petrol in a diesel? Don’t start the car. Tell the station, arrange recovery, and get the system drained properly-starting it can turn a simple drain into a pump/injector repair.
• Does keeping the tank full prevent condensation? Keeping more fuel in the tank can reduce air space and moisture cycling, which may help in some conditions. The bigger win is avoiding regularly running very low and buying from good stations.
• Can supermarket fuel damage my engine? Generally, no-UK fuel is regulated. Differences are more about additive packages and station turnover than “bad fuel”, though any station can have a contamination issue.
• Why does my car smell of fuel after filling up? It can be a loose cap, a spill, or sometimes repeated overfilling affecting the vapour system. If the smell persists or you get warning lights, get it checked promptly.