H6 Octane Requirements

[rayclark]

Does the H6 3.0R engine have to use premium fuel otr can regular be used without issues?

 

Thanks

 

RC

[monk50]

Does the H6 3.0R engine have to use premium fuel otr can regular be used without issues?

 

Thanks

 

RC

 

Have 05 LL bean outback with 27000 miles on the clock. Been using midgrade without any problems to date.

 

monk50

[porcupine73]

Pretty sure the requirement is 87 octane, I don't think it's a 'high' compression engine or anything, unless you have a spec b or something then it might have 10.7:1 and be able to use 95. Plus your knock sensor might help if there's any real issues.

 

edit: i stand corrected; cars101.com says for the LLBean it's 91 octane.

[gbhrps]

My wife's Lexus ES 330 is supposed to use midgrade octane fuel. With 52 000 kms on the odometer and using only 87 octane since new, there have been no issues to date. The car is seldom asked to "get it on", and even then there is no pinging indicating pre-ignition. My 90 Nissan 300ZX with 72 000 kms gets a diet of 87 octane as well. The manual says to use only premium, but I'm long past hotdogging my toys. And the very few times that I've hammered the throttle, I have yet to hear any pre-ignition. The computers of modern cars compensate for the octane variances, and unless you drive hard and demand performance most of the time, I would think that you would be safe using a lesser octane. Just keep an ear tuned for pinging when using WOT. If you hear it, back off and change to a higher octane with your next tankful. You may well find that you can get along without the premium fuel and price.

[ShawnW]

Definately Use premium. Thats a very expensive engine to have trouble with and its not worth the risk. I know a guy that blew one of the H6 3.0's up and it cost him 10,000 dollars to have the engine replaced at the dealership.

 

Its ABSOLUTELY a high compression engine.

[Manarius]

I'd go with whatever it says in the manual.

 

I'd like to know how running 87 and not getting pinging is going to cause "problems down the road."

[ShawnW]

Low octane fuel causes carbon buildup in engine which results in the tops of the pistons becoming caked with carbon and ring landings to be plugged full of it as well. Also, the newer cars like the LLBeans and Tribeca are VERY well soundproofed and you might not even hear it pinging.

 

(and nobody listens to their stereo loud and everybody always pays attention to their engine sounds and not their fellow passengers, cell phone, navigation system, radio, CB, etc.) And do you really want to have another thing to worry about over a 3 dollar a tank difference? The world has enough stress thrown around without adding unnecessarily to it.

 

Stick with listening for clicking CV axles like the rest of Subaru owners.

[Ranger83]

Definately Use premium. Thats a very expensive engine to have trouble with and its not worth the risk. I know a guy that blew one of the H6 3.0's up and it cost him 10,000 dollars to have the engine replaced at the dealership.

 

Its ABSOLUTELY a high compression engine.

What fuel was the guy who blew up an H6 using? What year? How many miles? I searched long and hard for evidence of any problems with H6's - including searching this board. Why is this the first time I've heard of an H6 that "blew up?" Did you ever post this in an earlier thread?

 

Premium fuel is Recommended by SOA - not Required (for turbo 2.5's, it's Required). And, it makes absolutely no difference in how the H6 engine runs.

 

I have been switching back and forth between premium and regular every several thousand miles after 1,000 miles of break-in. We log all fuel use and there is no difference in fuel economy and no perceived difference in performance.

 

"Aha," you might say, "But maybe the engine management system is retarding the spark with the lower octane fuel and thus masking any performance difference."

 

That's possible. So, I brought my car to an AWD dyno facility and had them run it at full power - on regular. Then, we checked the engine logs. The spark timing was in the normal range and there was no sign of any detonation: regular has enough octane to drive the car at full throttle without problems.

 

"Aha," you might then say, "But SOA says you have to use Premium." Nope: [emphasis added]

 

Thank you for taking the time to contact us. We hope that you have been enjoying your 2006 Outback 3.0R Wagon.

 

The 3.0-liter H6 engine is designed to operate using unleaded gasoline with an octane rating of 91 AKI or higher. Regular unleaded gasoline with an octane rating of 87 AKI or higher may be used. This is not just for emergency situations. You can use regular unleaded fuel in your vehicle on a regular basis. However, for optimum engine performance and driveability, it is recommended that you use 91 AKI or higher grade unleaded gasoline.

 

You may experience reduced output, poor accelerator response, and reduced fuel economy when using gasoline with an octane rating lower than 91 AKI, depending on your driving habits and conditions.

 

If you experience any of those conditions while using a lower octane rated fuel, you may want to return to using 91 AKI octane rated fuel as soon as possible. Additionally, if your vehicle knocks heavily or persistently, or if you are driving with heavy loads such as when towing a trailer, the use of 91 AKI or higher grade unleaded gasoline is required.

 

Thank you for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again.

 

Best wishes,

 

John J. Mergen

Subaru of America, Inc.

Customer/Dealer Services Department

 

So why would SOA recommend Premium? Possibly to get a higher hp rating. But we'll find that out as well - with another dyno run using high octane.

[1 Lucky Texan]

What fuel was the guy who blew up an H6 using? What year? How many miles? I searched long and hard for evidence of any problems with H6's - including searching this board. Why is this the first time I've heard of an H6 that "blew up?" Did you ever post this in an earlier thread?

 

Premium fuel is Recommended by SOA - not Required (for turbo 2.5's, it's Required). And, it makes absolutely no difference in how the H6 engine runs.

 

I have been switching back and forth between premium and regular every several thousand miles after 1,000 miles of break-in. We log all fuel use and there is no difference in fuel economy and no perceived difference in performance.

 

"Aha," you might say, "But maybe the engine management system is retarding the spark with the lower octane fuel and thus masking any performance difference."

 

That's possible. So, I brought my car to an AWD dyno facility and had them run it at full power - on regular. Then, we checked the engine logs. The spark timing was in the normal range and there was no sign of any detonation: regular has enough octane to drive the car at full throttle without problems.

 

"Aha," you might then say, "But SOA says you have to use Premium." Nope: [emphasis added]

 

 

 

So why would SOA recommend Premium? Possibly to get a higher hp rating. But we'll find that out as well - with another dyno run using high octane.

 

When you were switching back and forth and dyno-ing the car, did you reset the ECU each time and allow it to adjust the timing for the fuel?

 

Carl

[Ranger83]

When you were switching back and forth and dyno-ing the car, did you reset the ECU each time and allow it to adjust the timing for the fuel?

 

Carl

No. New Subaru ECU's have some sort of non-volatile memory so they can't be reset without plugging it in. That's why I drive at least two thousand miles on each grade. That usually takes about a month.

 

In the next couple of weeks I'm taking it back to the dyno for a run on Premium, and without any air cleaner.

[Ranger83]

I'd add a caveat - some of these Regular grade fuels with the ethanol additive seem to have lower octane than rated.

 

Lately several friends have taken to buying mid-grade 89 because of detonation in several different cars.

[Ranger83]

Update. Car now has 32K miles on it. I've been using regular exclusively for at least six months. No problemo.

[Legacy777]

As Subaru said in their response, using lower octane fuels may cause poorer performance & mileage, and may cause knock under certain circumstances. Most fuels will meet and exceed their AKI rating, so if you're buying an 87 octane fuel, the chances are, it may be a few points above.

 

The way the ECU's work, they will constantly monitor the engine knock sensors, and will push timing up until the point of knock. The chances are that if you drove around on premium for a while, and then had the car dyno'd the timing trims would probably be slightly higher.

 

Also, in regards to resetting the ECU. The fuel & timing trims should be able to be erased by resetting the ECU, or pulling the battery.

[robm]

Remember that AKI or "pump octane" is an average of the octane rating measured 2 slightly different ways. One method is called "research", the other "motor". Research gives a higher number. Some fuels have a very high research number, but a lower motor figure, but they average out the same as a fuel with a high motor octane, but a low research.

 

And guess what? Usually, a real engine prefers (knocks less) with a high motor octane number compared to one with a high research octane number.

 

So, not all 87 octane fuels are created equal.

 

And guess what else? Usually, high motor octane fuels are more expensive to make than high research octane fuels.

 

So cheap gas may well be not as good for your engine, especially if it is built for a higher octane number, but a better quality low octane fuel may be just fine.

 

I learned all this many years ago, working at an oil refinery, where I was often found hanging out with the technician that measured the octane ratings of the product, and of the competitors' product.

[Phizinza]

My question would be what fuel economy do you get with 87 vs 91 octane rated? I've always found the higher octane almost (and in some cases always) pays for itself in economy.

[Ranger83]

///The way the ECU's work, they will constantly monitor the engine knock sensors, and will push timing up until the point of knock. The chances are that if you drove around on premium for a while, and then had the car dyno'd the timing trims would probably be slightly higher.

 

Also, in regards to resetting the ECU. The fuel & timing trims should be able to be erased by resetting the ECU, or pulling the battery.

Ih ad the car dyno'd on regular and there was no evidence in the logs that detonation was occuring.

 

You can reset the ECU as you describe on older Subarus buit not 2005+.

 

My question would be what fuel economy do you get with 87 vs 91 octane rated? I've always found the higher octane almost (and in some cases always) pays for itself in economy.

I have logged all fuel use since new. Last year's log was posted on subaroutback.org. I switched between grades every 2,000 miles, until I became convinced that there was no discernible difference.

 

Subaru "recommends" 91 octane but the mid grade fuel is 89 and premium 93. I've tried them all. The variation due to driving is much more than any difference in fuel. This also means it would be easy to convince yourself one particular grade of fuel got better mileage.

[Phizinza]

The variation due to driving is much more than any difference in fuel.

Yes, I get between 22 - 30 mpg in my EJ22 Brat, always on the same fuel. Some days I just like to open her up.

I personally couldn't see how a small difference in octane rating could blow up your engine. Or even leave some deposit within just say 100K miles. Make sure you run cat friendly injector cleaner and upper cylider lube every so offen as well to keep things clean and running good.

[Ranger83]

Another update. 35,000 miles, no problems, going in for another dyno run in two weeks.