What are the consequences of mixing different types of fuels?. For example, say you had half a tank of Optimax (98 Ron) and topped up with standard unleaded (95 Ron) do the fuels mix and create something in between or do they remain seperated?. I really don't know much about fuels and fuel technology, but I would be interested to know more if someone could shed some light on it.

Shouldn't think there would be any reaction or separation, just a dilution of the overall octane effect. My previous Rover 1.6 16v came alive after a tankful of Optimax which I treated myself too every 3-4 fill ups. It was fun letting it wear off and enjoy the improvment again every couple of weeks!

You may be interested in the thread I started on a similar subjected - http://www.briskoda.net/forums/new-octavia/super-unleaded-97-ron-fuel-octavia-vrs-mark-ii/49914/

The consequences of mixing are minimal - they will mix but I would recommend against it. You will not get the (supposed) benefits until you fill from an empty tank, preferably the second time around using the same fuel.

I filled my car with Shell Optimax last night (into an empty tank) - http://www.briskoda.net/forums/new-octavia/fuel-gauge-how-far-can-you-go-warning-light/50067/2/. Whilst it will help improve performance, clean the engine and benefit fuel economy, I suspect that the most beneift will come from subsequent refills with the same fuel.

Have only used Optimax from new, but I was interested what the consequences of mixing fuels were.

Well, I should think a precise 50/50 amount of each would give you a nice 96.5 RON? With some good sloshing about to mix the two. (that's my logical mind coming into play)

So I'd say your performance should be somewhere between the two levels of performance.

Well' date=' I should think a precise 50/50 amount of each would give you a nice 96.5 RON? With some good sloshing about to mix the two. (that's my logical mind coming into play)

So I'd say your performance should be somewhere between the two levels of performance. [/quote']

Genius!!!, does this new accountancy job of yours mean that you are constantly trying to find stuff to calculate? :P

The mixing may not be that exact if the density of the two fuels differs.

Take a look at section 6.15 of this FAQ - http://www.faqs.org/faqs/autos/gasoline-faq/part3/

It's more important to fill up your tank at the right time (usually when it's empty) and not just put a little bit of fuel in every now and then according to how much cash you have.