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I have recently purchased a 2005 Mazda6 Wagon. I am a bit confused as to which petrol type I should be using, 91, 95 or 98.

The company that sold me the car and also the local Mazda dealer suggested the higher the octane rating the better mileage. However the car sales also suggested mixing it up ie half 91 and half 95 or 98.

Is it false economy using 91 and is there a possibility of doing damage to the engine?

One BP station I went to only had 91 or 98, others have 91 or 95.

Gary

From the "Ask Jack" archives - 24 December 2009

I assume the car is fitted with the 2.3litre engine.

If this is the case the correct fuel is 95 (or higher).

One of the key fuel requirements is governed by the engine compression ratio and for this reason I would not recommend using 91 Octane.

The engine management system may well allow the lower octane fuel to be used but engine performance and fuel consumption may suffer.

The 98 Octane fuel is available for high performance engines that require a fuel rating higher than 95. I don't believe there is any advantage in using 98 over 95 in your case but this is where it gets a little complicated.

The BP stations you mention are normally the super sites which only sell 91 and 98 Octane fuel and really do take advantage of the public such as yourself. If you don't want to use 91 then 98 is the only option.

If you can find an alternative BP gas station or use another fuel brand where 95 is more readily available then I suggest you use it. Adding 98 is not going to do any harm, it simply means you are paying more than you need to for the correct fuel.

If the car has a 2.0litre engine then 91 Octane is the correct fuel to use. Once again no harm if you use a higher octane, but no benefits either in my opinion.