Best Gasoline For Your Car Engine? Not Always Premium Gas

by Guest Blogger on 2010-02-2825

Ready for a science class? Here’s something a little different. This is a guest post by Mr. Credit Card from www.askmrcreditcard.com. Today, Mr. Credit Card is going to be talking about the difference between regular and premium gasoline and why you may actually be paying more for your gasoline than you think.

All gasoline is a combination of many different hydrocarbon molecules, ranging from heptane (seven carbon atoms and 16 hydrogen atoms) to decane (10 carbon atoms and 22 hydrogen atoms) and beyond. But the stuff we get from gas pumps is the hydrocarbon identified as octane. The octane number you see at the pump is not actually a measure of the percentage of octane in the gas itself but rather, measures how that gasoline compares with a pure mixture of octane and heptane.

What is an Octane Rating?

Octane, by definition, is the resistance to burn (e.g. detonation resistance) in a car engine. A higher rating means that the gasoline will burn slower when it is ignited in the engine. Therefore, for high compression engines, a higher rating of octane means that there is better control over the gasoline burning. So the goal for every consumer or car owner should be to choose the right octane level or rating for their car engine’s design so that their car’s consumption of gasoline is done with maximum fuel efficiency (and hopefully cleaner emission).

premium gas vs regular gas?
Image from Cagle.com


But to understand this whole concept of matching fuel type to engine, we must first understand the concept of “knock”. “Knock” is the explosion that takes place in the car engine that’s described as an “unregulated explosion”. It happens when the compression of fuel and air in your engine sets off an undesired explosion; when this happens, you’ll hear a loud noise that’s bad for your engine.

Should You Use Regular or Premium Gasoline?

So what type of fuel should you choose for your vehicle? Well it really depends on your engine, and more likely depends on when your car was manufactured.

Older Engines: Older engines use carburetors to regulate air/gas mix. Unlike modern engines which use computers and sensors, an old engine cannot accurately regulate air and gasoline levels consistently. Therefore, carburetors need adjustments during a car’s regular maintenance to ensure that they keep the proper air and gasoline proportions as specified. When adjustments are not made on a regular basis, too much fuel will be mixed with air and the gasoline that does not burn gets turned entirely into carbon deposits. To solve this problem, you could turn to using higher octane or premium gasoline to prevent the “knocking” in your engines.

Newer Engines: Modern engines use fuel injectors with computers to accurately control the air/fuel mix under all temperature levels and in any environment. However, the accuracy of the fuel injectors and computers is based on using the recommended gasoline for that engine, which depends on the engine’s compression ratio. Hence, to make sure that the fuel injector computers work properly, you’ll have to use the right type of fuel.

Most car engines are built and designed to burn regular unleaded fuels with an octane rating of 87 (i.e. regular). High performance sports cars (or higher performance cars) have higher compression ratios and need higher octane (e.g. premium 89 or 92) to avoid knocking.

If your vehicle needs a higher octane rating of 89 to 93, you should find this documentation in the owner’s manual, as well as possibly under the fuel gauge and by the fuel fill hole. Usually you will see this rating for high performance engines only.

To find out what type of gasoline to use, check your owner’s manual. Using premium gasoline isn’t going to help your engine if all you need is regular unleaded gasoline. The bottom line is to use the type of gasoline recommended for your engine. This may help you to trim gas costs.

Ending Thoughts

There have been lots of other posts discussing numerous ways to save money on car expenses. Examples include buying fuel efficient cars and avoiding gas guzzlers. There’s the debate about whether to buy new or used cars (used cars are a great deal). You could also lower your car insurance rates by choosing to own a Honda Civic rather than a BMW convertible. These are choices every car owner has to make based on his or her lifestyle and finances. But I’ve found that many folks assume that paying for “premium gasoline” will “prolong the life of their car engine”.

In some cases, you have to use “premium gasoline”. In many cases, “regular gasoline” will do. The point is, if you don’t know which type of gas you should use, then you might just end up paying a lot more for fuel in the long run. And that is really throwing money away. In addition to using the correct type of gasoline for your car, you should also try these other money-savvy moves: use a gas credit card or a cash back credit card that pays more than 1% on gasoline purchases so you can save money in the long haul.

Tip: Check your car manual right now. Knowing which type of gas to buy could very well save you a good amount of money in the long run!

Copyright © 2010 The Digerati Life. All Rights Reserved.

{ 25 comments… read them below or add one }

Manshu February 28, 2010 at 8:39 pm

This is certainly quite interesting, I just assumed a higher number was always better.

LeanLifeCoach February 28, 2010 at 8:54 pm

You are better served to spend an extra few dollars on routine service than on premium gas!

Mr Credit Card February 28, 2010 at 10:04 pm

I found out that my Honda Oddyssey needed only regular gas and we’ve been using the middle grade for quite a while!! But I also found out that the recommended gas for my Lexus 350 was premium and I had been using the middle tier one all along!!

Check your manual. Better yet, check your manual before you even buy the car!

Danielle February 28, 2010 at 11:48 pm

Great article!

My ex-husband was a Honda salesman and he always stressed to me (because, of course, I drove Hondas – and still do) that their cars ran best on the lowest octane. I’ve always remembered that and I’m thankful whenever I can save a little extra at the gas pump.

Kosmo @ The Casual Observer March 1, 2010 at 7:23 am

I’ve always used the cheapest gas (per the instructions in my cars’ manuals) and have never had a problem with the engine. Then again, I’ve always had a pretty high highway:city ratio on my miles.

kenyantykoon March 1, 2010 at 9:37 am

if there ever was an area that i am totally green in, it is cars and gas and all the science under the hood. i have never had a car, you see and since i am still here(haven’t died yet), i think i will continue using the bus for the next few years until i am in a position to buy a car whose costs i can very easily maintain

Goran Web Design March 1, 2010 at 10:14 am

Paying the premium for something that has no benefit seems rather ludicrous, yet so many of us commit this sin when it comes to purchasing fuel. Unless you’re running a forced aspiration or high performance motor car, the lower octane gas will do just dandy!

Credit girl March 1, 2010 at 3:21 pm

It’d certainly be a smart idea to check what kind of gas your car needs. That can save you lots of money at the pump! Sometimes, I just wish I could buy the lowest costing gas but my car requires premium.

Mr Credit Card March 1, 2010 at 8:26 pm

Credit Girl – just out of curiosity, what is your car?

basicmoneytips March 3, 2010 at 5:22 am

I have heard this before and actually agree with it. I drive a 2003 BMW 325 and it says to use the high octane gas (91 or 93 I think). I have been putting in 87 octane for about 2-3 years now, and it seems fine. Occasionally I will switch to 89 or 91 for a tank, but not regularly.

Knock on wood, everything seems fine. I hope that I do not harm my engine over time, but so far I see no ill effects. Not that I am advising this, just my story.

The Rat March 5, 2010 at 3:48 pm

Nice post; I always go for the regular and not the more expensive premium gas.

Eric March 22, 2010 at 4:48 am

I knew this all along but too bad my Acura TSX requires premium gas per the manual. Oh well.

Car Repair Advice April 21, 2010 at 1:23 am

Huh, this is really an important lesson for all us drivers. There are many reasons for car problems caused by bad gasoline. So every driver should be aware and should know what kind of gasoline they need for their car, and how to choose the right one.

Mike @ Arizoan Trust Deeds April 22, 2010 at 5:45 pm

Yeah, my corvette knocks a little if I try to use anything less than the highest octane.

nottingham auto centre May 25, 2010 at 9:19 am

Recently in the UK, there was a major incident when a large supermarket was supplying very low grade fuel at its pumps, cars were taken to garages to flush the system and fuel was replaced. tut tut

earnest June 7, 2010 at 9:16 pm

Gasoline or petrol has always been pretty straight forward for me, but the new fuel cells from Honda may have changed the ground rules completely. This is especially so, as they have now invented a way to get Hydrogen using solar power to refill the cars that run on hydrogen. A great article by the way, very informative. We all need to know what fuel octane rating runs best in our vehicles.

Kerin August 3, 2010 at 2:01 pm

I do think that its best to stick with well know, branded petrol stations. I’m not sure if premium is really worth it? As already mentioned, it’s best to save that few extra $’s and put it aside for your next car service or repair :)

Bill Estes December 7, 2010 at 3:23 pm

Premium gas is such a waste of money. I agree, putting money aside for your next service or repair is better than wasting it on the pump.

On a “green” note, I’ve been reading recently that several companies are experimenting with an algae based fuel. I’m not sure exactly how it works, but it certainly sounds like an interesting way to go. It’s great to see groups starting to get more environmentally active and looking for alternative fuel sources!

canuck901 April 4, 2011 at 6:06 am

You’re kidding me? you’re a fool if your car is supposed to run on premium gas and you use regular. Your engine will carbon up, ping noises, and carbon buildup over the years will affect the engine. It will cause high maintenance bills. Spend the extra money on premium gas and you can avoid expensive repair bills. If you don’t want a car that needs to run on premium fuel, then don’t buy one!

misty May 16, 2011 at 3:15 pm

I am driving a 2007 Pontiac G5 and I switched to supreme, will that ruin my engine?

Silicon Valley Blogger May 16, 2011 at 3:44 pm

I would check with the manufacturer or your dealer for the details. Each car has their own requirements after all.

akmbenz July 11, 2011 at 10:36 am

I drive a 2007 Mercedes E350. The manual calls for premium gas, A good friend of mine who is an engineer told me that the new high end automobiles have sophisticated computer systems that can sense the octane levels of the gasoline and adjust the timing accordingly to prevent knocking. The manufacturer’s urge you to use high octane fuel in order to achieve the horsepower that they boast about in their advertising. Using a lower octane fuel and retarding the timing results in less horsepower.

Interestingly enough, by using regular gas I am achieving more than a 5% increase in mpg while also saving 25 cents or more a gallon. I detect absolutely no knocking whatsoever. The comment made earlier that lower octane fuel will gum up your engine is simply not true…. all gasoline has detergents to prevent this.

Gas Man July 20, 2011 at 12:35 pm

I have people tell me all the time that i have enough gas and don’t need anymore!!

Barbie March 21, 2012 at 12:46 am

I don’t regularly tune my car, so far so good. that “Knock” thing is scary though, I don”t want to experience that. :)

Some people told me that ethanol free gasoline is much better for my carburetor type car, but it’s hard to find a station that sells that nowadays (In my country).

Thanks for sharing this though! Keep it up!

DAX June 4, 2012 at 11:52 am

In Oct 2010, I bought a brand new Honda Accord EX-4WD V/6. From day one I have been using the mid-grade gasoline in it, though according to Honda Dealer it is OK to run the car on Regular Gas. If I change now to regular, will it any way impact my engine? Please let me know.

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