Quick Facts About Your Car’s Gas Requirements
- Learn about fuel requirements before buying a used car because the additional cost of premium gas means less money in your wallet.
- Spending more on high-octane fuel is a waste of money unless the car’s high-compression engine requires premium gas.
- If the owner’s manual recommends regular unleaded, premium fuel won’t make the engine run better or produce more power.
Many drivers ask these questions, and too often, they come up with the wrong answers: Will premium gasoline make your car run better? Can regular gasoline damage your engine? What about the middle — does midgrade fuel give you better gas mileage? We’re here to help you decide which kind of gas to put in your car.
- What Type of Gas Does My Car Use?
- What Octane Gas Should I Use?
- Does My Car Need Premium Fuel?
- Why Do Some Cars Need High-Octane Fuel?
- When Can I Use Regular Gas?
- Can I Choose the Kind of Fuel I Use?
- What If My Car Says RON 95 or RON 98?
- Buying Gas at High Altitudes
- Diesel and E85
What Type of Gas Does My Car Use?
Find your car’s minimum octane rating in the owner’s manual. Vehicles requiring premium fuel will usually say so on or near the gas cap and sometimes even by the fuel gauge. If your car specifies premium gas, use the high-octane pump. Otherwise, there’s usually no reason to buy anything but the lowest-priced regular gasoline.
Check on fuel requirements before buying a used car because you might need to factor in the additional cost of higher-octane fuel into your budget.
What Octane Gas Should I Use?
The best type of gas to put in your vehicle is whatever octane level the car’s owner’s manual specifies.
Generally, here’s what you need to know about octane gas types:
- Regular fuel is 87 octane
- Premium is 91 or 93
- Midgrade falls somewhere in the middle, often 89.
To understand what octane means, we first have to look at the concept of preignition. Engines compress a mixture of air and fuel and ignite them with a spark. Under certain conditions, the fuel-air mixture can prematurely ignite. This is called “preignition,” which makes a knocking sound similar to a coffee percolator. Nowadays, most cars have knock sensors that prevent preignition, so you’ll rarely hear it.
Octane measures the gasoline’s resistance to preignition; the higher the octane, the less likely it is to detonate. Contrary to what some believe, high-octane gas has the same energy content as low-octane gasoline.
MORE: What Happens if You Overfill Your Gas Tank?
Does My Car Need Premium Fuel?
If your car says “premium fuel required” and the owner’s manual specifies 91 or 93 octane, you should always fuel up with the pricey stuff. Back in the day, using low-octane gasoline in a car that required premium would likely cause damage. In a modern vehicle, the knock sensor can retune the engine on the fly to avoid preignition, but this will most likely reduce power and fuel economy. Along with showing a false economy, engine damage is still possible.
Why Do Some Cars Need High-Octane Fuel?
It’s all about the compression ratio. Some high-output engines use a higher compression ratio to produce more power. They compress the fuel-air mixture to a smaller size, creating extra heat that can cause the fuel to ignite prematurely. These high-compression engines need high-octane fuel to ensure the gasoline doesn’t combust early.
If your car has an engine that requires premium gas, it will say so in the owner’s manual. If you don’t see it in the manual, look for guidance that’s sometimes written on or near the gas cap or by the fuel gauge.
Is Gas With Higher Octane Worth the Price Difference?
Premium gas typically costs 75 cents or more per gallon than regular gas. That’s an additional $11.25 for a 15-gallon fill-up. Choosing the more expensive 89-, 91-, or 93-octane is only worth the price difference if your car requires higher-octane gasoline, such as midgrade or premium fuel. Otherwise, you would be wasting money. Always use the fuel recommended by your owner’s manual.
When Can I Use Regular Gas?
If your car manufacturer recommends regular 87-octane gas, you’re in luck. You can safely use the cheap stuff. Premium fuel won’t make the engine run better or produce more power. There’s simply no benefit to buying premium gas unless there’s a difference in the ethanol content.
It’s not uncommon for regular gas to be up to 15% ethanol (often called ‘E15’) and the premium option to be ethanol-free. Ethanol is a less efficient fuel than gasoline, meaning ethanol-free gas will always be more efficient than gas with any ethanol in it. However, the extra cost of ethanol-free premium gas over regular E15 is often more than what you’ll save with the slight difference in fuel economy.
Can I Choose the Kind of Fuel I Use?
If your vehicle says “premium fuel recommended,” you have a choice — you can run regular, midgrade, or premium. Although the difference may be slight, these engines generally develop more power and better fuel economy on higher-octane fuel. However, using regular gas won’t damage the engine or void your warranty. We advise running a few regular and premium tanks and calculating your fuel economy. Decide for yourself if the differences in power and fuel economy, if even noticeable, are worth the extra cost of premium fuel.
Does Gasoline Go Bad?
Volatile compounds in gasoline degrade over time, and the combustibility of old gas decreases, even when properly stored. Gasoline can get contaminated by things such as dirt and rust. Refresh old gas by mixing it with a high ratio of fresh gasoline. Contaminated gas should not be used to power any equipment because it can damage the engine’s components.
What If My Car Says RON 95 or RON 98?
Some European cars specify RON 95 or RON 98 — but don’t worry, you don’t have to look for 95 or 98 octane fuel. These are European octane numbers calculated using a method different from the one used in the United States. RON 95 is equivalent to 87 octane in the U.S., and RON 98 equals 94 octane; for the latter, 93 octane fuel should be sufficient. Simply put, RON 95 means “regular,” and RON 98 means “premium.”
Buying Gas at High Altitude
When traveling at high elevations, you’ll likely see gas stations selling lower-octane fuel — for example, 85-octane regular. The old-school thinking behind this notion is that thinner air effectively lowers the engine’s compression ratio, so lower-octane fuel is suitable.
That reasoning may work for old cars with carburetors and minimal emissions systems — and we’re talking old vehicles built before 1975. But modern fuel-injected engines detect the lower oxygen content of the air and adjust themselves accordingly. Therefore, they’ll be expecting fuel of the recommended octane. These engines can compensate for lower-octane gasoline, but only so much.
So, we recommend you go by the numbers when driving at high altitudes. If your car requires 87 octane, use that, even if it means buying midgrade. If your vehicle requires premium fuel, you may not be able to find the high-octane gasoline you need. Plan ahead. Fuel up at low altitudes. If you don’t think you can make it back to lower altitudes without gassing up, buy the minimum quantity you need of the closest octane you can find.
Try to add fuel while there’s still some left in the tank; the higher-octane fuel will effectively dilute the lower-octane fuel, so the average octane in the tank will be closer to what the car needs. Fill the tank with high-octane gas as soon as it’s available.
Diesel and E85
If your car has a diesel engine, you must use diesel fuel. Diesel engines use a different process to ignite and burn fuel. They won’t run on gasoline, and fueling up with gasoline can result in expensive repairs. Most diesel vehicles say “diesel fuel only” on or near the fuel filler.
E85 is a blend of 85% ethanol and 15% gasoline. Some gasoline-powered vehicles, known as flex-fuel vehicles, can also run on E85; they usually have a bright-yellow fuel cap. A flex-fuel vehicle running on E85 pollutes less but generally gets around 30% worse fuel economy. Don’t put E85 in your car unless you’re sure it’s E85 capable. The car may run, but you’ll likely void your warranty.
TIP: Check the owner’s manual or check for labels by your gas cap to determine the fuel that the manufacturer recommends or requires and use that fuel.
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Editor’s Note: This article has been updated since its initial publication.
Put fuel cleaner in it and go to a different gas station and get regular then go back to the other gas station telling them there gas is bad and almost ruined yours car
I have a 1998 Dodge Durango 2.5
God what does this even say