eddie33081

So, I turned in my 2007 530 and was only putting in the "medium" flavor gas at 89 octane. I noticed that this new car 2009 535i has it written everywhere to put 91 octane. Is this a 100% necessity? My last car ran fine on 89 but this is turbo so Im not sure. Its a lease if that matters. Let me know what you guys use. Pros? Cons?

Thanks

Krozi

I would never go lower than 91. I always use 93. If you go too low, the knock sensor in the engine will cut performance to protect the engine. But, the lower octane fuel also has lower quality, and if it's not clean enough, the engine knock adjustment might not be able to compensate enough to prevent harm to the engine. You will probably not see any problems during the lease if you go lower, but it's really not nice for the next owner.

swajames

What's the point of taking any chances for less than $2 per tank difference? The car will adapt to the different gas, but it may not perform as well as it could or should. There's no real benefit in putting higher octane fuel in your car, it is set up for premium fuel at 91/93, but it's generally accepted that it's detrimental to performance to use a lower octane rated fuel. NB before the Euro crowd jump on and bash crappy US fuel, the US uses a different scale and 93 here is 97/98 or so in Europe...

gotabyte

It definitely makes a difference as your engine's compression is high. Higher octane is required to prevent pre-ignition of the fuel mixture(pinging) with high compression engines. Pre-ignition will damage an engine because it's firing the mixture on the piston's up-stroke. The computer will retard the timing in an effort to avoid the pre-ignition but it is not the best way to handle it. It's a duct-tape solution to the problem. Performance is lowered because of the reduced ignition timing. You will also burn more fuel so the savings is not there.

craigm1841

take care of the turbo'ed engine properly and put the better fuel in. i only use 93. if i can drive a 60 thousand dollar car, i can pay the extra 10 cents a gallon for fuel

Krozi

+1

dp2008

+1

Couldn't of said it better myself...
The Turbo is the main reason for the higher octane. Retarded timing also will lead to excessive heat in the combustion chamber causing burned valves and in exteme cases, pitting on your piston crown caused by pre-ignition.

jagbagri

If you drive 300 miles a week (about 60 miles a day per one work week)
and the difference between 89 and 91 is about 10 cents (pretty normal)
you get about 20 miles/gal. so about 15 gallons a week (roughly one fill-up a week, again pretty normal)
you will save:
15x$.10=$1.50 a week
or
$1.50x52=$78/year not to mention the lower fuel economy you will get. so I would say you would save roughly about $60/year.

Is it worth it to put your car through all this and risk further/more issues with your car down the road?
You don't need to answer, just think about it.

5_Is_Alive

+2

amit1947

Everyones comments on the knocking is true, but the comments about 87 and 89 being "lower quality" doesn't have any truth to them. The higher octane is just another blend of hydrocarbons to yield a slower burn time in the combustion chamber. Higher octane will cost more because of the extra steps required to produce the fuel. Just because 93 costs more than 87 DOES NOT make it a "better" or "higher quality" form of gasoline.