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Milledgeville, GA

1 recommendation

reply to Kearnstd

Re: [Tech] Which grade of fuel should I use

said by Kearnstd:

most 2000+ cars even if they state premium will adapt to lower octanes. A good example is my parents run their Outback XT on 89 instead of the manual's 93(premium) and the mechanic at the dealer said no harm would be done.

Nooooo! Your dealer mechanic is an idiot. Turbo Subarus have a pretty bad tune from the factory and can knock even on 93 octane. Running 87 octane on it will definitely shorten the life of the ring lands. It's also silly to buy a top model turbo vehicle and then be too cheap to spend the extra $2 per fillup. When something fails (and that's when, not if) the complaints will be all about how Subaru made a crap engine and not that it was fueled with water its entire life. I hope that mechanic can fix 'em because he clearly doesn't know how they're operated.

Saying cars will adapt to low octane is true but it is misleading. It's like saying your body will adapt to work on half its required caloric intake. Sure it will -- for a while. The factory spent all that time developing a timing map so the engine will deliver its rated performance over a wide range of operating conditions. Then there's a fallback map that makes sure you aren't stranded due to a bad tank of gas. Now you're asking the car to run on that map 24x7. They do have limits of how much timing can be pulled and you can still knock under throttle. That Subaru is probably pulling all the boost it can too. Anyone with free software & a laptop can see this in 30 seconds and I'd bet the farm that their ECU is not a happy camper.

Most garden variety v6s work fine with 87 because there's nothing special about them. Run regular in a Camry with no problem! The Hemi in my truck suggests at least midgrade but it gets 93 all the time because I'm not that cheap to fuel a higher-compression v8 with the minimum.

The OP's Stratus shouldn't require higher octane either. If it runs better with it, I'd look at Seafoam too, to get rid of deposits on the pistons that may be causing preignition.
John M - Cranky network guy

Hatboro, PA
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He didn't say that it was running on 87, he said they run the Subaru on '89. I'd be willing to bet dollars to doughnuts as well that the turbocharger gets a very light workout, so there is no harm in using 89 octane.
"from a broken heart to a hole in the sky"