i usuaully use the standard unleaded (95) when filling up but the petrol station was out of it today so i decided to go for a tank of the 98 variety... but what's the difference? i can't really feel any when driving (diddnt drive really far as the station was close to home). also, is it ok to mix the two? because i had a tiny amount of 95 still in the tank before filling up.

 

I haven't tried mixing fuels or higher octane gas in my mcs yet. In my fathers BMW 335is we do mix fuels fairly often though. Usually do half a tank of premium(91 octane) and the other half of the tank with 100 octane racing gas and there is a huge noticeable difference in performance gains in the BMW.

 

It looks like you guys in southafrica use the EURO method of determining octane....
In the US/NORTH AMERICAN MARKET, standard octane is 87 (wcecpt in some mountan areas where 85 is ok), midgrade is usually 89, and hitest is 91-94, depenging on the region, and regulation regarding volility, clean air rules, and which refinery....but since a different test is used to rate the fuel, R+M/2, THE NUMBERS are different as are the types of fuel....in the us fuel usually has 10% ethonol, and nolead...not sure about your stuff...
The euro mini boards likly will have more info about octane levels that work best.....
In the us jst above the midlevel, 90 is recomended on the level, more like 92-94 does get more hp, especially with a pulley and/tune.

 

Problem I face is that almost all the gas stations around here sell 87, 89 and 93 while the MCS calls for 91. I'm thinking about alternating 89 and 93 filling the tank when it is about 1/3 full.

 

My mini had half a tank of what I'm sure was 87 when I got it. Have had three fills since with 93 and over 1000 miles and I'm getting 32-36 mpg with very little highway driving. Cant really comment on performance,but love the miles per gallon!

 

Folks...look at the op..
he is in SOUTH AFRICA.....
They use the euro scale of octane....
So your Northamerican numbers do not matter....
what does matter is use what the car is made for...
gen1 mini's, yes your 2004 is a gen1 mini, REQUIRES midgrade. Running too low of a octane fuel IN A GEN1 MINI can result in serious mechanical issues. If you have a pulley, more octane is better, so most folks in my area just get the highest pump fuel (non race) ypu can buy in the area...that is 93 with the NORTHAMERICAN specs for fuel...likely 98 that you tried....
Generaly octane can be mixed, fuels are usually compatible.....

 

Its call predetonation and it happens in the 2nd gen also.

OP just run what the owner's manual tells you to run in the car. If yo9u don't have one talk to a dealership and ask them.

 

That sounds like a lot more hassle than just using 93 all the time, which will have no down side.

I put 94 in my Cooper simply because it has no ethanol, while other octane ratings all have 10% ethanol here.

 

On the topic of fuel, can using a higher octane hurt the engine at all? Im in the US and have access to race fuels of all octanes near my workplace. Can and should I spend potentially a lot of extra cash for a tank of high octane fuel for a weekend of driving? How much of a power increase would I really get with these richer fuels?

 

No it will not hurt the engine but, it is like a crack addiction.

 

Oh good. If u had said heroin id be worried but i think i can handle a tank of crack every now and then

 

It will be fine but, eventually you be turning tricks so that you can get that next fix. It is really a sad lonely road to race gas addiction.

 

I am afraid that the mini itself may be enough to turn me to the streets for extra cash so for now ill take the safe route and enjoy good ol' premium, at least until i get my abs back and my street value goes up.