The Octane Misconception

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#1638870 22-Sep-2016 16:49

The video at
http://autoexpert.com.au/buying-a-car/should-i-use-premium-petrol
explains it pretty well.
Warning: John Cadogan uses colourful language in the video and doesn't pull punches. References the Australian market, but the facts are just as relevant here.

And if you like that there is also "which fuel drives your dollar further" by the same author on YouTube.

Edit: Mods, I know this thread was originated prior to the being a car forum, but would suit being moved to it.

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#1638986 22-Sep-2016 20:29

richms:

My MR-S hates 91. Again, lent it, someone filled it with that and then bought it back saying they thought something was wrong with it. Totally different car with that stuff in it.

My 1ZZ-FE Corolla (Same engine) was fine on 91.

Cars can only pull the timing so much before they still start to pre-ignite and stick a nice big hole in a piston. If you're running a JDM Turbo on 91 that was designed for 100, you're asking for trouble. If you run an econobox that was designed for 91, you'll be fine.

I know older direct injection cars can struggle with 91 also, like Mitsi GDI and Toyota D4 engines.

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#1638989 22-Sep-2016 20:34

Question: are the additives in 98 BP fuel better? Is the 98 BP fuel cleaner?

Reason i ask is the new cars with direct fuel injection apparently suffer from carbon build up because the fuel bring injected bypasses something causing that thing to build up with carbon (?? Valves is it i think

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#1639092 22-Sep-2016 23:48

My Land Rover handbook lists 95 as the minimum, 98 upwards as the preference.

I've put 91 in it when there was no choice but it certainly seems to like 98 better. I actually had to ring my fuel card provider and ask them to get prices from BP for 98 as they did not list it! At the moment I use the other card that has discount on the pump price, but sometimes fixed price is cheaper in the bundu.

Not sure if they still do, but BP were offering 102 RON fuel in the UK.

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#1639098 23-Sep-2016 00:22

joker97: Question: are the additives in 98 BP fuel better? Is the 98 BP fuel cleaner?

Reason i ask is the new cars with direct fuel injection apparently suffer from carbon build up because the fuel bring injected bypasses something causing that thing to build up with carbon (?? Valves is it i think

No.

The video @Dingbatt posted above explains really well

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#1639105 23-Sep-2016 05:52

ajobbins:
joker97: Question: are the additives in 98 BP fuel better? Is the 98 BP fuel cleaner?

Reason i ask is the new cars with direct fuel injection apparently suffer from carbon build up because the fuel bring injected bypasses something causing that thing to build up with carbon (?? Valves is it i think

No.

The video @Dingbatt posted above explains really well

That's not what the AA says (paragraph 3). I'm not saying the AA os definitely correct, but how do you know the guy on the video is not wrong?

Ok dumb keyboard not working

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#1639106 23-Sep-2016 05:53

http://www.aa.co.nz/membership/aa-directions/driver/fuel-duel-2/

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#1639148 23-Sep-2016 08:04

joker97:
ajobbins:
joker97: Question: are the additives in 98 BP fuel better? Is the 98 BP fuel cleaner?

Reason i ask is the new cars with direct fuel injection apparently suffer from carbon build up because the fuel bring injected bypasses something causing that thing to build up with carbon (?? Valves is it i think

No.

The video @Dingbatt posted above explains really well

That's not what the AA says (paragraph 3). I'm not saying the AA os definitely correct, but how do you know the guy on the video is not wrong?

Ok dumb keyboard not working

From memory, Mr Cadogan is a qualified engineer and has been a motoring journalist for many years. Most of the stuff he comments on has been fastidiously fact checked, lest he get sued by the car companies he regularly criticises. Funny how the same piece of writing can be differently interpreted though. I thought the NZ AA article pretty much confirmed what was said in the video. But last time I compared at my local Z station, the difference between 91 and 95 petrol was 12c, not the 8c quoted in the AA comparison.

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#1639157 23-Sep-2016 08:21

I understand he's a qualified engineer. I'm not asking engineering questions but what BP puts into their 98 fuel to combat the problems caused by direct fuel injection - read here.

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#1639159 23-Sep-2016 08:27

Hmm edit button out of screen
Either way it doesn't worry me my car's recommended fuel could be anywhere between 95-100RON ... Subaru JP do not reply to English emails.

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#1639160 23-Sep-2016 08:34

Have you read the Japanese manual? (assuming your car came with one or is JDM hence your need to make contact in Japan)

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#1639163 23-Sep-2016 08:40

joker97: I understand he's a qualified engineer. I'm not asking engineering questions but what BP puts into their 98 fuel to combat the problems caused by direct fuel injection

http://www.goauto.com.au/mellor/mellor.nsf/story2/0065CFE44AAA997DCA257F7A002297AE

It's a higher octane = higher flash point = less prone to detonation issues.

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#1639164 23-Sep-2016 08:40

Didn't come with manual. English ones e.g. NZ say at least 95

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#1639186 23-Sep-2016 08:47

Thanks lsxw i understand octane.

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#1639344 23-Sep-2016 12:16

joker97: http://www.aa.co.nz/membership/aa-directions/driver/fuel-duel-2/

That article is riddled with inaccuracies and odd statements.

Just a couple of examples (there are more):

Unfortunately for motorists, it’s often unclear which ‘premium’ fuel (95 or 98 octane) is sold at which service station, as retailers are not required to display the price on the price board – only at the pump. On occasion, that means some motorists may unintentionally spend an extra eight cents per litre buying a higher octane fuel than the one they actually need.

That makes no sense. Why would the fact only the 91 price being displayed on the board someone make them fill their car up with a higher grade fuel than they need? I have never, ever seen a pump in New Zealand or Australia that doesn't have the octane grade displayed at the pump, along with the price. Sure, some may only have one either of 95 or 98, but it always has the octane rating (and the price) at the pump.

High-octane mineral fuels do have marginally higher energy levels than lower grades, so fuel economy may improve slightly.

And then

To see if there was any difference in economy, we ran a car designed to use 91 octane on 15 litres of that grade to measure its fuel consumption and then, when the car had completely run out of fuel and wouldn’t re-start, we refilled it with 15 litres of 95 octane and repeated the route until it too ran out. Our expectation was that, as higher octane fuels contain marginally more energy, there would be a slight improvement.

NO. That is the whole misconception and even the AA are perpetuating it *facepalm*

In Europe, 95 and 98 octane are the two most common grades; in Japan it’s 91 and 96/98 octane. In the USA, the fuel grades range between 87-91octane. Australia mostly uses 91 or 95 octane.

No mention of the fact that they aren't comparing things equally (I doubt they even know the difference by the rest of the article). The USA figures are AKI and the rest will be RON.

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