87 gas in 3.0 - Subaru Outback - Subaru Outback Forums
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post #1 of 9 (permalink) Old 04-26-2019, 11:09 AM Thread Starter
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87 gas in 3.0

I tried to find a thread regarding this, but I couldn’t... sorry if it’s been talked about before, but I was wondering if I can use 87 octane gas in my 2006 LL Bean edition 3.0 H6 engine.
The label on the gas tank door says
“Premmium gas RECOMMENDED”
(Not required).
Is there any negative long term effect on the engine besides reduced performance?
I’d like to hear from people who actually own 3.0 H6.

With the crazy gas price of today, every little bit of saving in running cost helps.... (the price different of 87 vs 91 gas is like 40-50cent/ gallon here...)

Thank you in advance.

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post #2 of 9 (permalink) Old 04-26-2019, 11:29 AM
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Don't.


You'll break ****.


It's expensive as all get-out, yeah, but so are internal engine repairs. lol


In all seriousness though, I believe aside from performance, I also noticed lower efficiency (<20mpg regularly) the few times I ran low-test gas. Best I can tell, too, is that premium prevents knock/pre-det and therefore overheating of some under-cooled cylinders, which will, importantly, prevent head gasket failure.


There's a link in my sig with my fuel-up history on my 3.0, but if you can't see it with your low post count (I think it does that), here's an actual link: http://www.fuelly.com/car/subaru/out...lickvdc/268019
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post #3 of 9 (permalink) Old 04-26-2019, 01:18 PM
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The great thing is you don't need to read or decide. Subaru says "Recommended" which means the door is open for 87. So, go test drive the car and see how it does for your driving with both choices and see what works for your engine condition and driving environment.

If 87 causes issues, then run premium. I run 87 95 percent of the time. I've never noticed a difference in at least 5 different Subaru H6's over 10 years including my current 270k and 190k cars.

If it's in poor running condition maybe higher octane would mitigate issues....but that's like swimming with a cheap band-aid and it needs maintenance not premium.

My daily commute is rough, low elevation, mountain switch backs so maybe that dumbs down the numbers and I don't notice small benefits, but I've seen zero difference. 27.xx mpg on flat Ohio roads a couple times a year, which is as high as average H6's will go, and again no change with premium or 87.

A time or three a year I try premium and non-ethanol premium during high load times to mitigate the engine work outs during towing/interstate/heat/humidity/mountains, usually I'm hoping to see a little difference....and I'm always disappointed..."was that better...different....faster....i think maybe..." but the gas mileage never changes. A decade and about 5 different H6 vehicles and it's been the same every time.
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post #4 of 9 (permalink) Old 04-27-2019, 01:08 PM Thread Starter
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I find it interesting one of you experienced drop in mpg where as another saw no difference at all....

Thank you for your inputs.
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post #5 of 9 (permalink) Old 04-27-2019, 01:24 PM
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if you go into high altitude you may want to pump the high octane, even if you run around on low octane. (pings is what you will get,)

I pump 93 into my 2002 H6, just trying to avoid it being a daily driver. when I have tested personally with it, going from 93 to 91 caused stumbling as it was slowly digesting the change.
(2001-2004 H6 have a more simple telemetry system, then your 2005-2009 H6,...and in my older car it takes about half a tank to smarten up to the lower octane being fed).

so yours maybe smarter on swapping back and forth for testing.

but lots of people with tunes here on their 2005-2009 H6, and good knowledge of plugs / octanes to go with the tune.
( XRT performance tuning = @west_minist is the typical tuner for the EZ30 cars,...I don't know if he has ever worked for lower octanes or fuel economy ....but maybe)

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post #6 of 9 (permalink) Old 04-27-2019, 02:48 PM
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Unless you are looking to extract max performance out of it, no reason to spend the extra money. Using clean, fresh fuel from a high volume station is just fine. The average driver won't know the difference, and the knock sensors will adjust timing if needed. Unless the ECU has been tuned using something like a Cobb, it will run just fine 99% of the time, and the other 1% the ECU will compensate. The key here is fresh fuel, 'specially if its ethanol added, as it loses octane when exposed to moisture/heat.
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post #7 of 9 (permalink) Old 04-27-2019, 05:05 PM
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I tried that and did not notice anything as it takes a while for mine to adjust. BUT when I went back to premium after first running the tank down real low there was a noticable difference in preformance after the first 3/4 of gas burned, ran the same route twice in the same day. I did not see any other differences, ie weather etc so I'm back to premium only. I run in sport# mode all the time so running in lower modes might make a difference. I can feel the difference between modes in preformance but running on the freeway with cruse control set to 70 MPH switching between modes causes a blip in the gas mileage indicator but after that it returns back to the same MPG indicated for all 3 modes. Amazing to me when you try the " intelledrive" , lowest mode, how much power is missing I would expect an significant jump in MPG, but I don't see it on my car.
I almost had an accident because if that, was passing a lumber truck uphill and at altitude. Put the pedal all the way down pulled out only to discover I was only very slowly passing the long truck. A long line of other cars behind me had filled up the lane so I tried to get by and just barely did with cars comming down the hill and the trucker blowing their horns and my GF yelling at me . Took a while to discover that the dog going back and forth between my lap and hers had stepped on the round mode dial in the center console which puts the motor in low power mode. I asked the dealer how to disconnect this as it's a safety hazard in my view and was told that kind of modification would void the extended warrenty. But jamming a piece of hard plastic under the **** switch is ok.
Is it just me or too much drama in my life ????
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Last edited by vanman; 04-27-2019 at 05:09 PM. Reason: spelling,spaces
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post #8 of 9 (permalink) Old 04-29-2019, 08:54 PM
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Run 87 most of the time. Usually switch over to 91 during the hottest months or before a 2+ hour drive. Never noticed much difference.
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post #9 of 9 (permalink) Old 04-29-2019, 09:53 PM
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I consistently record mpg. Always get 2mpg better with premium. Prob'ly not worth it, but I stick to premium.

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