My 500 Sport gas cap tells me that it is hungry for 91 octane. The local filling stn offers 87, 89, and 93. Do you suggest selecting the higher 93 octane or lower 89 octane for optimum engine performance and life?

I know there are many arguments about octane rating and it's benefit or lack there of. I am of the opinion that the manufacturer has designed an engine to run with fuel of specific ignition properties. Therefore, I am keen to use the fuel octane that the manufacturer suggests. But I wonder, what is best if the recommended octane isn't an option?

TrailRatedRN said:

My 500 Sport gas cap tells me that it is hungry for 91 octane. The local filling stn offers 87, 89, and 93. Do you suggest selecting the higher 93 octane or lower 89 octane for optimum engine performance and life?

I know there are many arguments about octane rating and it's benefit or lack there of. I am of the opinion that the manufacturer has designed an engine to run with fuel of specific ignition properties. Therefore, I am keen to use the fuel octane that the manufacturer suggests. But I wonder, what is best if the recommended octane isn't an option?

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Basically the octane rating given by the manufacturer is the lowest octane fuel that can safely be used without risking damage to the engine. You can safely use a higher octane rating than this without any adverse effect whatsoever.

In your case, you should be using 93 octane fuel. Using 89 octane fuel in a car designed for 91 could permanently damage the engine and will almost certainly void your warranty.

Euro readers should also be aware that these are US octane numbers, which are different from the ones we're used to dealing with.

Hey, I posted in the USA forum so I wouldn't confuse the Euros. ;p

TrailRatedRN said:

Hey, I posted in the USA forum so I wouldn't confuse the Euros. ;p

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Ah, but the Euros may still want to help, not understanding that octane ratings may not have an international standard.

Might be an idea to ensure that the Fiat recommendations are using local, US, ratings, rather than just using a standard label for all markets. But a higher rating is always ok.

So what is the fuel rating across the pond?

Our 'regular' fuel is 95 RON which suits the majority of petrol cars, although you can get 'super' with 97 and 99 RON. But you need to convert that to US ratings.

US Octane ratings are actually in AKI (Anti Knock Index), which is an average of RON and MON.

jrkitching said:

Basically the octane rating given by the manufacturer is the lowest octane fuel that can safely be used without risking damage to the engine.

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You can safely use a lower octane at altitude though

TrailRatedRN said:

My 500 Sport gas cap tells me that it is hungry for 91 octane. The local filling stn offers 87, 89, and 93. Do you suggest selecting the higher 93 octane or lower 89 octane for optimum engine performance and life?

I know there are many arguments about octane rating and it's benefit or lack there of. I am of the opinion that the manufacturer has designed an engine to run with fuel of specific ignition properties. Therefore, I am keen to use the fuel octane that the manufacturer suggests. But I wonder, what is best if the recommended octane isn't an option?

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Where I am at in Texas, you can only get 87, 89, or 93 and that's the same as ever other state that I've lived in. I've never seen a pump anywhere in the U.S. that had 91, but I haven't been to every gas station in America. If you read the owner's manual, it says you can use 87, it just *recommends* 91. I've noticed absolutely no difference between using 87 and 93 in mine and this is one of those heavily debated topics on a U.S. based Fiat board that I'm on. I noticed no difference in power, no major differences in mileage, etc.

So to answer your question, if 91 (or the equivalent wherever you live at) is not available, just use regular and you'll be fine.

I'm using 99RON (uk) Tesco Momentum in my Abarth 500, as is my sister in law in her brand new Corsa VXR, they both show a very noticeable difference to normal 95RON!

griff74 said:

I'm using 99RON (uk) Tesco Momentum in my Abarth 500, as is my sister in law in her brand new Corsa VXR, they both show a very noticeable difference to normal 95RON!

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of course your cars are turbo. on the 1.4 I have noticed absolutely no difference using the richer mix jungle juice = )

TrailRatedRN said:

So what is the fuel rating across the pond?

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95 RON is 91 AKI so that's the standard fuel we use across the pond.
98 RON is 93 AKI which is the richer jungle juice, premium.


Since gas is so cheap in the states I would just stick with 93 if you cant find 91 = )