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Regular Gas in Premium Gas Cars Won’t Save Much Money

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Mobilgas GulfWith gas prices on the rise (something that always seems happens as the weather gets warmer), everyone is trying to find ways to cut down on the cost of filling up each week. If you’re one of the many “premium” car owners, you’ve probably considered putting regular unleaded in your tank instead of the more expensive premium fuel – don’t.

You know how premium gasoline in a car that only needs regular gasoline will see no benefit? (it’s known as the high octane gas myth – premium fuel doesn’t correspond with a higher miles per gallon) Regular gasoline in a premium engine is less efficient and you don’t save as much money as you’d think. Your miles per gallon with a premium fuel in a premium engine is higher than with regular fuel in that same engine.

Autoglance did scoured the web for some self-reported figures and discovered that across eight luxury vehicles, the cost per mile saves was less than one cent per mile. The MPG with premium gasoline (91 or 93 octane), which on average cost $3.75 per gallon, was obviously higher than with regular (87 octane), average cost of $3.47 per gallon, but it was higher by a large enough margin that the cost savings per mile shrank to about half a cent. This wasn’t a scientific study and ultimately the best answer is to do the test yourself but the results show that chances are you won’t come out a winner (and it’s not a large enough difference to even warrant a test).

The lesson from this isn’t new, that you should use the fuel your car tells you to use, but it is confirmation.

Have you done any similar tests? I would give it a try except I don’t have a car that takes premium fuel (and we already know premium fuel in a regular car is meaningless).

(Photo: somegeekintn)

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15 Responses to “Regular Gas in Premium Gas Cars Won’t Save Much Money”

  1. JB says:

    I drive an Audi that takes premium, but I swiched to regular back when premium was over $4/gallon. I have not noticed a performance or MPG difference at all. I wonder how much driving style or highway vs city factors in when combined with the gas you use?

    • Mark says:

      Well don’t start complaining and blaming Audi if your engine starts getting problems…

      • Tony says:

        The folks at CarTalk did the exact same study and there will be NO DAMAGE by giving regular gas to an engine designed for premium. They backed this up by checking with the American Petroleum Institute, the American Engine Rebuilders Association and even a chemist at a major gasoline company.

  2. Alan says:

    You should also mention that putting regular gas in a Premium gas car can cause knocking and hurt your engine.

    The octane rating is for how far you can compress the gas air mixture before it combusts. The lower the rating, the lower the pressure. So if you put in 87 octane gas in a 93 octane car, the gas air mixture will combust at the wrong time screwing up the timing of your engine. Then all sorts of bad things starts to happen.

    Always use the minimum manufacture recommended octane for your car.

    • Well said. My wife sometimes forgets that my car requires higher octane gas and puts the cheap stuff in. I can tell as soon as I drive the car because it knocks like crazy.

    • tara says:

      A friend of mine filled my car with regular gas instead of premium my vw suggests, and my engine has knocked a couple times. Will I need to do anything or will just running the premium will correct the problem?

  3. Nick says:

    I drove a 1997 Geo Metro until 2009… needless to say that wasn’t a premium gas car…..

    I don’t expect to ever drive a premium car, unless I buy one more than a few years old, but the way I look at it is I won’t buy anything that I’m not prepared to support the right way.

    So I won’t go out to eat unless I’m prepared to tip at least 20% for example (of course, if the waitor spits in my drink he’s only getting 18%…haha). And I won’t buy a premium car unless I have the money to maintain it and put the appropriate gas in it.

  4. Good rule of thumb: if MPG is what you’re looking for in a car then you’re probably looking for a car that runs on regular anyway. A car running on premium is probably the type of car where MPG is not the main feature.

    That said, some new cars, like the Sonata Turbo have engine management to run on any fuel. MPG isn’t supposed to suffer, just a wee loss in power.

  5. Jason says:

    Most cars can run on most fuels due to variable valve timing and knock sensors. What you want to pay attention to is the minimum octane rating for your vehicle. The best way to save money on MPG is tire pressure. Your loosing way more in MPG if your tires are under or over inflated. The second thing to really take a look at is running better lubrication, ie engine oil, chassis lube, differential, etc. Those are all areas of friction, and to sound like a typical commercial…reduce friction and engine buildup you get more MPG. Typically the 20$ oil change specials use absolute crap oil. Spending a marginal amount more you can move into a synthetic oil that will increase mpg and more importantly reduce wear.

  6. freeby50 says:

    Interesting.

    I think the answer is not as clear cut. The article cited collected several reports from individuals. So this isn’t very scientific, its just a survey of what people said on the Internet. I’m not doubting what they say, but its not extremely rigorous.

    I looked at one of their sources and it was a message forum. I found several people there saying that they got 1 MPG difference. That 1 MPG could make 89 octane cheap gas more cost effective. For example, one person reported 23 MPG with regular and 24 MPG with premium. If premium is $3.9 and regular is $3.7 then they’d be spending less per mile on regular. (0.161 $/mile versus 0.163) But if you change the price of gas theres eventually a cross over point where that 20 cents /gal difference doesn’t matter as much as the 1 MPG improvement. If regular was $5 and premium was $5.2 then the improvement from 23 to 24 MPG would make premium cheaper.

    Some cars may compensate for lower octane by having less engine power. But the individual driver may then compensate for less power by depressing the gas more which then lowers MPG. So less power could effectively end up causing less MPG assuming the driver continues to drive the same way.

    If 20 cents a gallon matters that much to your budget then you’d usually be better served by downgrading your car.
    Generally cars that require premium gas are higher end premium cars. There are a handful of exceptions where relatively cheap cars use premium just to milk the most MPG.

    • Jim says:

      Yeah it would be nice to see a more scientific study done by maybe a Motor Trend or some car magazine with the resources to try a variety of cars.

      Good point on downgrading your car though.

  7. yourPFpro says:

    I have seen many studies that delve into this issue. The common theme I’ve seen though is that every situation is unique. There are so many different factors that come into play depending on your car, driving style etc. that you can not definitively say your car needs premium gas or doesn’t.

    So I split the difference and put in midgrade :)

  8. eric says:

    Well my Acura states premium gas and that’s what I’ve always used. There were about 2 times when regular gas was used (I lent my car to people and they didn’t know better). I did notice then that the gas would empty quicker but that’s not exactly scientific. Still, I stick with what the manual says.

  9. Scott says:

    What I have never understood is why is the price difference between regular, mid grade and premium the same ten cents no matter what the base price is? For example:
    regular 2.10 3.75
    mid grade 2.20 3.85
    Premium 2.30 3.95
    Are we to believe the additives used to create the higher grades have never changed in price over the years??? Why doesn’t the gap increase in actual dollars, and stay basically the same as a percenage. The way it is now, premium becomes more of a bargain as the base price increases, if the differnce does not increase.

  10. Anthony says:

    I drive a 2006 HHR with the 2.4L engine. The manual “reccomends” premium but the previous owner ran regular in it without any problems, and from what I’ve read, you can put regular in it without any issues as the engine will adjust its timing to prevent knocking. The vast majority of my driving is city and I was getting about 23-24mpg on regular (right where EPA estimates said I should be)

    I switched to premium just to see if there was a difference, and besides improved engine performance, my mpg went up to around 26! I didn’t change my driving habits or anything. Doing the math I figured it was actually cheaper to put premium in my car, but to the tune of a couple dollars over the course of a year.

    In the end, everyone’s car is different and the only “rule” I can come up with is that if the manual says to put premium in there, it might actually work out better


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