Lower octane = worse mpg ?

Rory · 07-16-2016, 10:56 AM

I usually use Shell V power which is 99 ron (uk). The last tank I filled up with BP Ultimate which is 97 ron.

My mpg is usually about 24/25, and now its struggling to stay at 22. I reset it every tank I fill up... it was below 20 at some points with town driving.

Does the higher octane fuel really give better mpg ?

Kevinl · 07-16-2016, 12:12 PM

You need whatever is premium in your area and yes the lower octane can decrease mileage as the ecu will retard timing to prevent detonation which will hurt performance and efficiency

CanadianTSi · 07-16-2016, 12:49 PM

97 ron is still 93 North American Octane and 99 Ron = 94, so no that's not going to cause a difference in MPG. Heck even if you filled up with 87 the car wouldn't knock just cruising around in vacuum. WOT would be a different story but nobody gets 25mpg at WOT.

07-16-2016, 10:56 AM	#1
Rory Lieutenant 93 Rep 299 Posts Drives: E92 335i SE 6MT Join Date: Aug 2013 Location: Lanarkshire, Scotland iTrader: (0) Garage List 2005 Z4 3.0 6MT [0.00] 2007 335i 6MT [0.00]	Lower octane = worse mpg ? I usually use Shell V power which is 99 ron (uk). The last tank I filled up with BP Ultimate which is 97 ron. My mpg is usually about 24/25, and now its struggling to stay at 22. I reset it every tank I fill up... it was below 20 at some points with town driving. Does the higher octane fuel really give better mpg ? __________________ 2007 E92 335i 6MT \| MHD Stage 1 + \| Mishimoto Intercooler \| Z4 Airbox mod
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07-16-2016, 12:12 PM	#2
Kevinl Lieutenant 210 Rep 563 Posts Drives: 2017 BMW M3 Alpine White 6MT Join Date: Aug 2014 Location: Phoenix iTrader: (0)	You need whatever is premium in your area and yes the lower octane can decrease mileage as the ecu will retard timing to prevent detonation which will hurt performance and efficiency
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07-16-2016, 12:49 PM	#3
CanadianTSi Captain 207 Rep 602 Posts Drives: 2014 535 xDrive Diesel Join Date: Feb 2007 Location: Alberta iTrader: (0)	97 ron is still 93 North American Octane and 99 Ron = 94, so no that's not going to cause a difference in MPG. Heck even if you filled up with 87 the car wouldn't knock just cruising around in vacuum. WOT would be a different story but nobody gets 25mpg at WOT.
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