Using a lower octane fuel than recommended

[The Critic]

Does anyone use a lower octane fuel than the one recommended by the vehicle manufacturer?

Theoretically, any situation where the ECU has to pull timing in order to prevent detonation should have some impact on efficiency. However, I am curious if there are any applications where the savings from running a lower octane still outweighs any increase in fuel consumption.

 

[Malo83]

Not recommended.

 

[Ed_Flecko]

I never do this, but I'm one of "those people" that thinks if the owners manual recommends it...I folllow it. I think the engineers must have had a good reason for people to follow their guidelines.

But...that's me.



Ed

 

[Brian123]

I did this 1 time since the gas station near me was out of 89 and 93, my car calls for 91. I was low on gas and filled up with 87, car ran ok but it seemed low on power.

 

[walterjay]

The opposite here. My 1.6 Turbo Hyundai recommends 87. Runs poorly on it and I use 89 and the difference is incredible, especially pulling a hill.

 

[Jimmy_Russells]

Pretty much any modern car will deal with it, but you'll make less power and potentially have other issues with LSPI or similar. For the few bucks a tank, why even worry about it?

 

[aquariuscsm]

I tried it in my 300ZX one time and the engine pinged like crazy.

Don't do it.

 

[slacktide_bitog]

Early 4th gen Maximas recommended premium (recommended, but not required). I always used regular and had no problems at all

 

[FZ1]

Does anyone use a lower octane fuel than the one recommended by the vehicle manufacturer?

Theoretically, any situation where the ECU has to pull timing in order to prevent detonation should have some impact on efficiency. However, I am curious if there are any applications where the savings from running a lower octane still outweighs any increase in fuel consumption.

Lots of tests of premium vs. regular gas. No real difference in mpg. Regular burns a little hotter.

 

[The Critic]

Pretty much any modern car will deal with it, but you'll make less power and potentially have other issues with LSPI or similar. For the few bucks a tank, why even worry about it?

Mainly because it is difficult to prove any longevity issues due to the lower octane. If the financial savings support the decision and the driver is not concerned about driveability, there is a case.

Also, the knock sensors only detect the knock under conditions where the ECU has knock detection turned on....which is not under all conditions.

 

[Kira]

The wisdom I grew up hearing was, "the proper fuel results in a cooler burn".

Because I regularly take highway trips, I have proven the improved economy and brighter operation from proper fuel (designated octane) many times.

 

[javacontour]

Just rental cars at higher elevations.

As long as I'm not driving it hard, probably no damage done.

 

[kschachn]

Lower octane fuel does not burn hotter nor cooler, have more or less energy content, burn faster or slower, burn less or more completely, ignite less or more easily, nor does it make you dinner. A required octane rating in the owner's manual is what the engine design requires as a minimum and if the ECU is able to alter the ignition timing then it may be able to make use of a higher octane gasoline to be more efficient. Where that efficiency increase falls in relation to the higher price for the fuel is hard to determine since AFAIK no one publishes efficiency numbers in their owner's manual.

 

[Zee09]

I was trying to escape the $1 more a gallon but on 93 octane my car gets the best mpg and is absolutely far nicer to drive and I did get the price down to about 30 cents more a gallon than 87 octane.

But top tier Exxon gives the best results so far.
It cost what it cost and I decided to just suck it up.

My car does require premium to be clear.

 

[skyactiv]

Guys, this is why the auto makers want a new high octane standard fuel. If you want to buy a new gas vehicle down the road, it will need to run on a higher octane gas than the 87 octane we are addicted to. There is more to it than I have time to say at the moment.

 

[WylieCoyote]

Knock sensors tell the ECU when to pull timing, to keep detonation under control. But, detonation has to occur before the knock sensors will act.

Detonation is akin to striking the tops of the pistons with a hammer. Do you really want this happening repeatedly during a drive, to save a few bucks?

 

[kschachn]

Guys, this is why the auto makers want a new high octane standard fuel. If you want to buy a new gas vehicle down the road, it will need to run on a higher octane gas than the 87 octane we are addicted to. There is more to it than I have time to say at the moment.

Higher compression leads to better thermodynamic efficiency because the corresponding expansion ratio is higher. It is a legitimate means of increasing efficiency but at a cost for the fuel.

 

[Zee09]

Sunoco offers the 91 octane here but you save only 10 cents a gallon over 93... Not worth it to me as once I get to a half tank I top it off.

 

[BMWTurboDzl]

No.

 

[MRC01]

Lower octane fuel does not ... have more or less energy content ...

Most of your statement was true, but this part is questionable. Some of the additives added to gasoline to increase its octane (such as ethanol) have less energy per unit volume than the gasoline they displace. Gasoline is around 115k BTU/gallon. Ethanol is around 76k. So ethanol has higher octane but less energy. Blending more ethanol into the gas increases its octane but lowers its energy content.

PS: If the engine can take advantage of the higher octane to use more aggressive timing (valve or spark) to increase power, it offsets (whether completely or partially) the lower energy per volume of higher octane gas. Higher efficiency means squeezing more out of less. But only if the engine is designed to do that - otherwise, higher octane fuel is giving reduced efficiency & power. Generally speaking, I advise using the lowest octane gasoline that enables your engine to run at peak efficiency without pinging. If it wasn't designed for high octane, then running high octane has no benefit, and might actually reduce efficiency & power, not to mention costing more.