Will my M Roadster run on 95 unleaded?

[AllTorque]

Anyone done it?

[Smartie]

it's all ours ever got and we had no problems. Our current E36 M3 gets that too and seems happy enough!

[rich_b]

It'll probably run a bit rough and not produce quite as much power, but it'll still run.

>> Edited by rich_b on Tuesday 28th September 22:01

[hughjayteens]

IIRC the ECU retards the ignition a little running 95 RON so it will be down on power, but still run OK.
The handbook states you should only ever use 97 RON so I see no reason why not to! The difference in cost is minimal, and if you get more power then why would you not want to use it!?

[AllTorque]

I always use the 97 or Optimax. Just wondered if I'm desperately low and if the nearest petrol station doesn't sell either, is it best to go with the 95 or freewheel further on....

[juliann]

I would suggest you'd notice naff all difference between 95 & 97/8. There are other important factors such as ambient temperature etc.. which will affect the performance.

97/98 is recommended for its RON values, but its also down to the 'Driveability Index' - which is :

DI = 1.5 x T10 + 3 x T50 + T90 (T being vapour temperature)

Ironically, the lower the result (down to about 495) the greater the driveability. High resulting fuel (inc Optimax) is best avoided in cold conditions.

However, you are also looking for 'Start - up' performance, which is expressed thus :

FVI = RVP + 0.7 x E-70

Unfortunately, in UK, maximum permitted Vapour pressure (as measured using the Reid method) is lower than that which is optimal for performance. The permitted pressure has reduced by over 20% since 1986, and a further reduction will occur in 2005.

To summarise, RON rating is only part of the story - next time you fill up just ask the attendant to do a quick Flexible Volatility Index test for you.

Having said that, I am a marketing mans wet dream and only use 97/8

[rich_b]

juliann said:

Lots of complicated stuff

mmm

[topboss]

Why not just stick to 97/8......the cost difference is marginal!

[AllTorque]

Because not all petrol stations sell it that's why!

[topboss]

touchy. Don't have that issue.......infact haven't been to a petrol station within the last 2 years that doesn't sell SU. Why don't you just top up with regular plus some octane booster.

[midgetmagoo]

I have occasionally used 95 in an emergency but try to use Optimax. Can't say I had a problem with 95 but she has a sticker on the dash that states 98 only should be used. She does drive a LOT better with Optimax (not sure whether this is just in my head though). Way I figure, better to pay a couple of quid extra every tank full rather than a couple of hundred quid for her to be fixed.

[bor]

I think your manual will say "optimum performance with 98RON, Fuel grades down to 91RON can be used without problems but with less performance/worse fuel economy.

So 95RON is no problem.

[AllTorque]

Read the manual? Now that's a novel idea....