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Old 09-30-2018, 12:06 PM
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Miss Rita Miss Rita is offline
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gas mileage

My wife has a Mini Cooper S, and I have a VW GTI. Both are turbocharged, and both are an absolute blast to drive.

Premium fuel is recommended by both manufacturers, but I've been told by the respective dealers that it's OK to use mid-grade fuel, the engine computer will reduce boost and retard the timing to prevent detonation. Understandably, they will make less power. For my day to day driving I'm OK with only having 190 HP on tap instead of the full 210 HP. I get 30 mpg for daily driving, 33-34 mpg on the highway.

Question: is gas mileage decreased when I use lower octane fuel? If there's no difference, I can save $15/month if I use mid-grade instead of premium. If mileage improves by 10%, the extra 10% in cost is justified.

Last edited by Miss Rita; 09-30-2018 at 12:45 PM.
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Old 09-30-2018, 12:12 PM
slalomjunkie slalomjunkie is offline
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Quote:
Originally Posted by Miss Rita View Post
Question: is gas mileage decreased under these conditions? (I can save $15/month if I use mid-grade instead of premium. LOL!)
I've used both 93 and 87 octane in my vehicles and never noticed a difference in how many miles per tank. And no detonation. Not even in the boat.

In fact, i haven't seen a car do that since the mid 70s

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Old 09-30-2018, 12:30 PM
calebbroege calebbroege is offline
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Upper grade fuel really is only needed for serious performance vehicles like sports cars or exotics for the most part


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Old 09-30-2018, 12:39 PM
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JimN JimN is offline
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Quote:
Originally Posted by Miss Rita View Post
My wife has a Mini Cooper S, and I have a VW GTI. Both are turbocharged, and both are an absolute blast to drive.

Premium fuel is recommended by both manufacturers, but I've been told by the respective dealers that it's OK to use mid-grade fuel, the engine computer will reduce boost and retard the timing to prevent detonation. Understandably, they will make less power. For my day to day driving I'm OK with only having 190 HP on tap instead of the full 210 HP.

Question: is gas mileage decreased under these conditions? (I can save $15/month if I use mid-grade instead of premium. LOL!)
Save half a buck every day, eh?

Does your gas have Ethanol? You would be better off without that crap than worrying about high OR low octane.
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Old 09-30-2018, 12:47 PM
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Quote:
Upper grade fuel really is only needed for serious performance vehicles like sports cars or exotics
Of course! Did I mention that we drive a Cooper S and a GTI? LOL!

Last edited by Miss Rita; 10-04-2018 at 02:39 PM.
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Old 09-30-2018, 01:45 PM
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lashburn1 lashburn1 is offline
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Originally Posted by JimN View Post
Save half a buck every day, eh?

Does your gas have Ethanol? You would be better off without that crap than worrying about high OR low octane.
I was just doing the .50 a day math when I read your comments.
Funny right...I guess everything adds up if you find enough things to save a Buck or 2 on...
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Old 10-01-2018, 11:50 AM
jharmon203 jharmon203 is offline
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I would use what the manual recommends. The engine is programmed to get a certain type of fuel. If you aren't using that (especially with turbo charged engines), then you are potentially getting that much more carbon in your engine due to the need for more of a fuel requirement. If you save $15 a month, that's about 180 a year. See what is costs to get your turbo replaced and compare the differences.

I'm not a mechanic, but I have done a fair amount of reading on turbos (due to buying an f150 ecoboost) and you probably dont want to mess around with a different fuel grade other than the recommended one.
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Old 10-01-2018, 12:26 PM
roadster02 roadster02 is offline
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Fuel octane ONLY has to do with the compression ratio of the engine. There is no more power, or fouling, or carbon production in the engine, or any other "urban legend" effect caused by high or low octane. 100 octane = the same power produced as 86 octane. Higher octane fuels have additives to reduce detonation in high compression engines, that's all. If you use a low octane gas in a high compression engine you can cause "pinging" which is pre ignition of the fuel and this can damage an engine, so, higher octane gas has an additive the helps by retarding the ignition point of the gas so that the heat of higher compression will not detonate it prematurely. Use a lower octane and listen to your engine, if it pings on hard acceleration, or when pulling a load, go up in octane. Better yet, read the owners manual and just use what is recommended for your vehicle.

Last edited by roadster02; 10-01-2018 at 12:44 PM.
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Old 10-01-2018, 12:32 PM
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$15 bucks savings?


Use premium. Do not listen to your dealer, they didn’t manufacture the engine.
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  #10  
Old 10-01-2018, 01:04 PM
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neil.anderson63 neil.anderson63 is offline
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Wife drives a GTI - 100% Premium fuel. We figure it’s pennies to avoid major dollars in repair bills.
Amazing car. I think she gets higher MPG running Premium vs lower grades of fuel.
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