Do I really need premium gasoline?

[BlueHouse]

Gas prices are going down, but still expensive for premium gasoline.  My car's manual says I should use high-octane (91-93) gasoline.  I want the generic version.  Can I do it? 

[zz_marcello]

In most cars you can use Regular Fuel (US standard 87 Octane) even when its not recommend.
Manufacturers have to make sure that engines are not getting damaged also with this lower fuel quality.
Its best to look in your owners manual.

(US Standard 87 Octane (Regular) equals European 91 Octone standard (phased out Normal Bleifrei in Germany))

[ZiziPB]

Try medium grade and see if your car will accept it.  I had several cars in my life that required premium fuel - most were doing just fine on medium.  I did have one, however, that refused to play nice on lower octanes.  When I tried medium grade, the engine started knocking and losing power, especially going up a hill.

[Jack]

In a modern car, using lower-octane fuel generally shouldn't damage the engine (but I might still be worried if the car is turbocharged). However, it could cause timing to be retarded far enough that the loss in fuel economy cancels out the savings.

[JLee]

Gas prices are going down, but still expensive for premium gasoline.  My car's manual says I should use high-octane (91-93) gasoline.  I want the generic version.  Can I do it?

What car?

[Gone Fishing]

The question has been answered, but it reminds me of an interesting experience on a road trip to Colorado around 12 years ago in my Honda Civic.  I noticed the engine pinging a bit on steep grades.  Having never pinged before, I attributed it to the high altitudes as we were over 10,000 ft. at times.  At the next fill up I noticed that "Regular" was only 85 octane!  I paid my dime a gallon more to get 87 octane "Mid-grade" and it ran without a hiccup.   Not sure if it is still that way or not.     

[BlueMR2]

Manufacturers have to make sure that engines are not getting damaged also with this lower fuel quality.

They do so with knock sensors that retard the timing when pinging is detected.  Those sensors are fragile and prone to undetected failures as they age.  A little ping here and there likely won't kill an engine too fast, but heavy sustained pinging will.  YMMV...

[bobechs]

In a modern car, using lower-octane fuel generally shouldn't damage the engine (but I might still be worried if the car is turbocharged). However, it could cause timing to be retarded far enough that the loss in fuel economy cancels out the savings.

This is true, and the best way to know if it is happening to you is to run a test with a couple of full tanks of each grade in the same driving and climate conditions, then calculating the mpg of each option.

This will be hard if you drive little and go months between fill ups, or don't drive a standard route.  One long weekend trip pitted against daily urban commuting can radically skew results. Also, reading the ø mpg on the dashboard readout if your car has one is not a calculation.

[BlueHouse]

Thanks everyone.  I think I have my answer. 

[Fishindude]

I've done a lot of work for a guy that owns multiple convenience store / gas stations as well as a fuel hauling and distribution company.
He told me they tested the different higher grade fuels in their automobiles to see if mileage increased enough to justify the higher priced fuel.  Their findings were NO, it did not.   He said the only reason to run a  premium grade fuel is if your car runs poorly on the standard grade fuel.

[Jack]

I've done a lot of work for a guy that owns multiple convenience store / gas stations as well as a fuel hauling and distribution company.
He told me they tested the different higher grade fuels in their automobiles to see if mileage increased enough to justify the higher priced fuel.  Their findings were NO, it did not.   He said the only reason to run a  premium grade fuel is if your car runs poorly on the standard grade fuel.

If your engine was designed from the factory to use regular, then putting higher-octane fuel won't do a damn thing because the engine timing with regular octane is already as advanced as it's gonna get. If your engine was designed from the factory for premium, then running premium in it is better.

Engine computers are designed to retard engine timing when necessary, but they aren't designed to advance it beyond factory spec. You could make your designed-for-regular-octane engine benefit from premium, but you'd have to modify it (e.g. by increasing the compression ratio or supercharging) to do so.

[Giro]

What kind of car?

If you have a car that is turbo or super-charged, don't put cheap gas in it.

[Malum Prohibitum]

Gas prices are going down, but still expensive for premium gasoline.  My car's manual says I should use high-octane (91-93) gasoline.  I want the generic version.  Can I do it?

  Do you think the engineers are just playing a practical joke on you?  If they say to use 91 or higher octane, then use it.  If you have a high compression engine, using a lower octane causes detonation, what some call "spark knock." That is the sound of gasoline exploding before the spark plug lights it up.   What this means is that the gasoline burns early, and a flame front travels down to meet the piston on its way up.  You are actually hearing the result of that collision.  It is like smacking the piston with a hammer.

This is nothing like the controlled burn that happens exactly when it is supposed to happen, when the spark plug lights off the mixture, pushing down on the piston at the correct time.

Anyway, detonation can break the piston and ring lands, but, more importantly, it will hammer out the rod bearings (top half) over time.  I have personally witnessed this many times.  You tear down the engine after it starts knocking, and the top half of the rod bearings has lost all of its coating.

Bad news.

For everybody else reading, your car probably does not require 91 or 93 octane.  That is because YOUR car is designed to run on a lower octane rating. 

For you, Bluehouse, your car needs it.  They designed it expecting high octane to be used.  Lower octane will pre ignite.  It can survive this for a while, especially if you drive very easy with no hard acceleration, but over time you are hammering those rod bearings out.

If you do not like buying high octane gasoline, then just buy a car designed to run on regular gas.   Most of them are, so it will be an easy switch.

[Malum Prohibitum]

I've done a lot of work for a guy that owns multiple convenience store / gas stations as well as a fuel hauling and distribution company.
He told me they tested the different higher grade fuels in their automobiles to see if mileage increased enough to justify the higher priced fuel.  Their findings were NO, it did not.   He said the only reason to run a  premium grade fuel is if your car runs poorly on the standard grade fuel.

  It has nothing to do with mileage.  If you have an engine designed for high octane fuel, however, you will get poorer mileage using lower octane as the computer tries to pull timing (retarding the timing) to get rid of the detonation.

If your car is designed to run on 87 octane, then you will actually get your best mileage using 87 octane.

[Malum Prohibitum]

In a modern car, using lower-octane fuel generally shouldn't damage the engine (but I might still be worried if the car is turbocharged). However, it could cause timing to be retarded far enough that the loss in fuel economy cancels out the savings.

  Not so.  Some modern cars requiring 91 octane can get by for a while on 89, but long term running them on 87 is a recipe for disaster.  Preignition occurs before the spark fires, so it does not matter at a certain point when you lower the octane too far that the computer is desperately trying to retard the timing, which, yes, hurts the fuel economy, as you noted, but the damage will still be occurring.

Running 87 octane in a car that the engineers designed to run on 93 is penny wise and pound foolish.

[Guardian]

Interesting topic to read.

I have a somewhat related question.

I drive a regular gas-sucker from 1997 with 165,000 miles on it. I've been told that using mid grade (89) is better for the engine because it can burn cleaner. Especially because I have an older vehicle and haven't dropped the gas tank and cleaned it. I did recently replace the fuel filter and it was doing its job (a few chunks found in it).

- Is it true that using the higher octane is better for the older engine and burning cleaner?

I also always keep the tank over 50% full, especially during the winter.

What are the thoughts on this?

[Telecaster]

Interesting topic to read.

I have a somewhat related question.

I drive a regular gas-sucker from 1997 with 165,000 miles on it. I've been told that using mid grade (89) is better for the engine because it can burn cleaner. Especially because I have an older vehicle and haven't dropped the gas tank and cleaned it. I did recently replace the fuel filter and it was doing its job (a few chunks found in it).

- Is it true that using the higher octane is better for the older engine and burning cleaner?

No, that is not correct.  High octane gas does one thing and one thing only:  It allows your engine to run at higher compression without knocking.  Higher compression = more power.  Knocking = bad. 

But if you have a normal engine that runs at normal compression, that high octane gas does exactly zero for you.  If it runs fine on regular gas, then that's all you need.   A lot of people think that high octane gas is better, or gives you more power or something.  But in order to get any advantage from high octane gasoline, the engine must be designed for it.  Hence the gas mileage experiment up above as described by Fishindude.    If the engine isn't designed for higher compression, higher octane gas gives you zero additional performance.   

[BDWW]

Gas prices are going down, but still expensive for premium gasoline.  My car's manual says I should use high-octane (91-93) gasoline.  I want the generic version.  Can I do it?

  Do you think the engineers are just playing a practical joke on you?  If they say to use 91 or higher octane, then use it.  If you have a high compression engine, using a lower octane causes detonation, what some call "spark knock." That is the sound of gasoline exploding before the spark plug lights it up.   What this means is that the gasoline burns early, and a flame front travels down to meet the piston on its way up.  You are actually hearing the result of that collision.  It is like smacking the piston with a hammer.

This is nothing like the controlled burn that happens exactly when it is supposed to happen, when the spark plug lights off the mixture, pushing down on the piston at the correct time.

Anyway, detonation can break the piston and ring lands, but, more importantly, it will hammer out the rod bearings (top half) over time.  I have personally witnessed this many times.  You tear down the engine after it starts knocking, and the top half of the rod bearings has lost all of its coating.

Bad news.

For everybody else reading, your car probably does not require 91 or 93 octane.  That is because YOUR car is designed to run on a lower octane rating. 

For you, Bluehouse, your car needs it.  They designed it expecting high octane to be used.  Lower octane will pre ignite.  It can survive this for a while, especially if you drive very easy with no hard acceleration, but over time you are hammering those rod bearings out.

If you do not like buying high octane gasoline, then just buy a car designed to run on regular gas.   Most of them are, so it will be an easy switch.

This ^!

Yes, modern cars have a knock sensor that can retard timing. Maybe it's not obvious, but if your knock sensor is sensing pre-ignition, you're already damaging your car. If it's working, and aggressive, it may prevent disastrous damage. But you're essentially depending on the fail-safe at that point. Definitely a poor decision in my opinion.

[Scandium]

How can higher octane be required/recommended in the US, but several places in Europe I've seen they don't even sell anything other than regular (91 octane?)? Can you even get it there, just in a few places?

[ZiziPB]

How can higher octane be required/recommended in the US, but several places in Europe I've seen they don't even sell anything other than regular (91 octane?)? Can you even get it there, just in a few places?

That's exactly it.  In Europe, the minimum octane is 91, so European cars like Audi, VW, BMW, etc. are designed to work at a minimum of 91 octane.  Which means that in Europe you would be using "regular" gas (91 octane) but in the US you need "premium" gas (91 octane).

[2Birds1Stone]

This sounds very penny wise, pound foolish.

[Scandium]

How can higher octane be required/recommended in the US, but several places in Europe I've seen they don't even sell anything other than regular (91 octane?)? Can you even get it there, just in a few places?

That's exactly it.  In Europe, the minimum octane is 91, so European cars like Audi, VW, BMW, etc. are designed to work at a minimum of 91 octane.  Which means that in Europe you would be using "regular" gas (91 octane) but in the US you need "premium" gas (91 octane).

Wait. Now I need to look into this. Is regular in the US lower octane than in Europe? I know the octane calcs are different. A while since I lived there, but remember there was 93, 95, and even 98 octane fuels. Neither of which I see anymore. I thought 87/regular here was same as 91 or whatever the lowest is in Europe?

edit: quick trip to wikipedia tells me regular gas in EU is usually 95 RON, equal to 91 AKI, or premium in the US. Regular (87 AKI) in the US is about 91 RON, but apparently not the most common in europe. So in general they do drive with higher octane rating there.

[Jack]

I drive a regular gas-sucker from 1997 with 165,000 miles on it. I've been told that using mid grade (89) is better for the engine because it can burn cleaner. Especially because I have an older vehicle and haven't dropped the gas tank and cleaned it. I did recently replace the fuel filter and it was doing its job (a few chunks found in it).

- Is it true that using the higher octane is better for the older engine and burning cleaner?

I also always keep the tank over 50% full, especially during the winter.

What are the thoughts on this?

I was going to say that regular was fine regardless of the vehicle's age, but then I started researching and read this:

We should note that even cars designed to run on regular fuel might require higher octane as they age. Carbon buildup inside the cylinder can create hot spots that can initiate knock. So can malfunctioning exhaust-gas-recirculation systems that raise cylinder temperatures. Hot temperatures and exceptionally low humidity can increase an engine's octane requirements as well. High altitude reduces the demand for octane.

So the answer is "maybe," but not because of gunk in the fuel tank but rather gunk in the engine itself. (In other words, to fix it you might use an additive like Seafoam -- if you think the gasoline doesn't have enough detergents already -- that you mix with the gas or spray into the intake. Cleaning out the gas tank is not necessary.)

In a modern car, using lower-octane fuel generally shouldn't damage the engine (but I might still be worried if the car is turbocharged). However, it could cause timing to be retarded far enough that the loss in fuel economy cancels out the savings.

  Not so.  Some modern cars requiring 91 octane can get by for a while on 89, but long term running them on 87 is a recipe for disaster.  Preignition occurs before the spark fires, so it does not matter at a certain point when you lower the octane too far that the computer is desperately trying to retard the timing, which, yes, hurts the fuel economy, as you noted, but the damage will still be occurring.

The same article claims:

Relying on these sensors, the engine controller can keep each cylinder's spark timing advanced right to the hairy edge of knock, providing peak efficiency on any fuel and preventing the damage that knock can do to an engine.

It sounds like modern engines are designed to run in the "almost-knock" zone all the time anyway, regardless of the fuel used, so if timing can be retarded enough I think they're claiming that abnormal wear can be entirely avoided. In other words, even on the fuel the engine is designed for (but not fuel beyond what it's designed for), the computer will be advancing the timing until it starts to detect knock so you'd still get the same wear anyway.

[BlueMR2]

If your car is designed to run on 87 octane, then you will actually get your best mileage using 87 octane.

This is true.  Beware though.  If you have an older car, today's 87 octane is not the same as the 87 octane of yesteryear.  Cars designed to run on 87 octane before Ethanol was added don't all run right on today's 87 octane due to the Ethanol (decreased fuel density).  I have an older "87 octane" car that when used with E10 requires a minimum of 92 octane to avoid pinging (we have 92 and 93 octane available here currently).  On the rare instances I can actually get real unmolested by ethanol 87 octane fuel, it will run on that...

[BDWW]

If your car is designed to run on 87 octane, then you will actually get your best mileage using 87 octane.

This is true.  Beware though.  If you have an older car, today's 87 octane is not the same as the 87 octane of yesteryear.  Cars designed to run on 87 octane before Ethanol was added don't all run right on today's 87 octane due to the Ethanol (decreased fuel density).  I have an older "87 octane" car that when used with E10 requires a minimum of 92 octane to avoid pinging (we have 92 and 93 octane available here currently).  On the rare instances I can actually get real unmolested by ethanol 87 octane fuel, it will run on that...

That doesn't make sense. Not running correctly, maybe, but pinging? Ethanol is higher octane than gasoline, it also cools better(avoiding hot spots).
E10 has plenty of problems, it's less power dense and it can damage seals, but pre-ignition is generally not one of them.  I suppose there could be some tangential effect...

But as a matter of course, hot rodders often tune to run on E85 for it's significantly higher octane range. It allows you to run at higher compression ratios and/or more boost in turbo/supercharged cars. You can literally double the power of a boosted car by tuning for E85.

[MudDuck]

As everyone else said, YMMV, but my car is a 2003 Mercury and it runs terribly on anything less than 91. I live in Pittsburgh, where everywhere you go is uphill both ways, and the difference is immediately obvious.

[Syonyk]

I've done a lot of work for a guy that owns multiple convenience store / gas stations as well as a fuel hauling and distribution company.
He told me they tested the different higher grade fuels in their automobiles to see if mileage increased enough to justify the higher priced fuel.  Their findings were NO, it did not.   He said the only reason to run a  premium grade fuel is if your car runs poorly on the standard grade fuel.

Higher octane fuel will not increase your mileage.  It's more likely to reduce it.

Octane rating is essentially "Preignition/detonation resistance."  Higher octane fuel actually has less energy per unit volume.  It just doesn't like to light off as easily, which is useful with high compression engines (or boosted engines, which are basically the same thing in terms of the conditions prior to ignition).

Do you think the engineers are just playing a practical joke on you?  If they say to use 91 or higher octane, then use it.  If you have a high compression engine, using a lower octane causes detonation, what some call "spark knock." That is the sound of gasoline exploding before the spark plug lights it up.   What this means is that the gasoline burns early, and a flame front travels down to meet the piston on its way up.  You are actually hearing the result of that collision.  It is like smacking the piston with a hammer.

Technically, preignition and detonation are two different things.  Preignition is when the mixture lights off prior to the spark event (usually from a carbon hot spot, or a helicoil tang that's sticking into the cylinder, or from a hot spark plug with damaged insulation).  Detonation is when the mixture "goes off" all at once (or close to it) instead of burning smoothly.  There are actually different levels of detonation, and while light detonation may be audible, medium and heavy detonation are what put holes in pistons.  However, detonation can cause hot spots that trigger preignition, and preignition usually transitions into detonation in one hell of a hurry from the increased temperatures and pressures at top dead center.

- Is it true that using the higher octane is better for the older engine and burning cleaner?

Nope.  That's a load of crap.  If the engine runs fine on 87 and doesn't ping under load, it's fine.

Newer engines will pull timing if they're on lower octane fuel (and, interestingly, some engines are pulling timing even on premium - people have found improvements going "beyond premium" octane.

But your owner's manual is a good guide.  If it says use premium, there's a reason for it, and not doing that risks engine damage.