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91 vs 89 Octane for 2011 BMW 535i engine

Dear Readers:

Is it critical to use the premium fuel or is the standard just fine for this engine? I understand I am getting less energy from the higher octane because of the additional additives.

It depends on what your owner’s manual says. If it says “premium required”, that means just what it says and you have to use premium or risk damage to the engine from preignition. If it says “premium recommended”, you can get away with using the lower octane juice without tearing up your engine. If you are trying to save money on fuel, and your owner’s manual says you can use lower octane fuel, try calculating your gas mileage with premium and compare it with lesser octane fuel. You may find that the lower fuel mileage you will likely get from the lower octane fuel either offsets or more than offsets the ten or twenty cents per gallon you save. In other words, it may be more expensive to run the cheaper gas.

Sunny Al

In the thread regarding warranty coverage on your new Beemer, I politely suggested that you need to read the details of the warranty coverage on your car. Those details are in your glove compartment, along with other documentation.

This thread leads me to a similar suggestion.
You REALLY need to read the Owner’s Manual that came with the car in order to get the authoritative word on this octane issue.

If the manual states, “91 octane gas required”, I think that is quite unambiguous.
If it states, “91 octane gas recommended”, that is a horse of a different color. In that case, you have been given an assurance by the manufacturer that your engine won’t be damaged if you use lower octane fuel.

Of course, your power output (and likely, your gas mileage) will be decreased with the use of lower octane gas, but if the manufacturer gives you an assurance that no engine damage will result, then that should give you some peace of mind regarding use of lower octane gas.

Please read the Owner’s Manual, the Maintenance Schedule, and the Warranty booklet that were provided by BMW if you want to derive the best use from your new car!

I think the high output turbo BMW engines, like the one in your 535i, are the exact engine I would use 91 in, all the time, no questions asked (at least by me).

You’re asking if you should use mid-grade or premium in a brand new BMW, a BMW with a twin turbo I6 no less? If I had just bought a $50k+ high end car, I’d probably use premium just out of principle alone.

It’s true that premium fuel has less energy than regular, but what’s much more important is that premium fuel has a higher anti-knock index and your car’s engine was designed for premium. There’s really no benefit from using regular in car that was designed for premium. Best case scenerio, you get less power and less fuel economy (since the knock sensors will reduce timing, and the ECU will fatten up the fuel mixture to prevent damage, using more fuel in doing so). Worst case scenerio, your knock sensors fail and you destroy the engine. Your warranty will not cover anything if you use a fuel with lesser octane than required.

For your specific car. If you look on page 241 of your owner’s manual. It says the following:

Required fuel
Super Premium Gasoline/AKI 91 or AKI
BMW recommends AKI 91 or 89.
Gasoline with lower AKI
The minimum AKI Rating is 89.
If you use gasoline with this minimum AKI Rating,
the engine may produce knocking sounds
when starting at high outside temperatures.
This has no effect on the engine life

So according to BMW, You can use 89 octane fuel, but there may be some minor side effects. 91 Octane is recommended. Personally with a turbocharged engine, I’d spend the extra 2 bucks a fillup for premium. You can try the 89 if you want and see if you take a hit in fuel mileage. Even a minor drop in mileage will more than offset the added cost of using premium though.

Note: It’s also possible they require 91 for the turbo engines and 89 for the N/A engines. You might want to check with the dealer about that.

But be careful about dealer advice. We just had a thread where a guy with an Acura asked his dealer, and his dealer told him regular was fine even though the owners manual says premium required. Dealers don’t always have the right answer.

“The dealer” often translates to either a car salesperson or a service writer/advisor, neither of whom is likely to know what the OP needs to know. These folk will likely give him a response, but whether it is a valid answer is another thing entirely.

Some of the misinformation that I have heard from the lips of car salesfolk has been…stunning in its stupidity. And, that service writer might have been working last week at Wal-Mart, stocking shelves, just before he magically became a service writer/advisor.

I can only repeat my advice for Sunny Al to finally open the glove compartment, take out the publications contained therein, and begin educating himself about the operation, maintenance, and warranty coverage on his expensive new car. I am sure that FoDaddy meant well by posting that information, but unfortunately this type of help is likely to keep the OP from actually reading the BMW booklets that he needs to become familiar with.

The real problem I have is that a person who was more than willing to shell out the money for a $50k+ car suddenly can’t open his wallet enough to put the required fuel into his gas tank every fill up.

Things like this make me wonder if he’s even using the proper BMW spec oil for the engine, and changing it at appropriate mileage intervals in his $50k+ car. Heck, does he even pop the hood, and check the oil level every couple tanks of gas, or is it running several quarts low right now, on incorrect oil, at a way longer oil change interval than non-spec oil should ever be used in this engine?

I feel sorry for the next owner who buys this car after the OP returns it after his lease ends, or when he wants to upgrade to the next bigger/better BMW they sell him in a couple of years.

I know I wouldn’t want to be the next guy to own that car.


Here’s the deal: if you use 87 octane your engine will try to compensate by retarding your ignition timing, which will effectively limit the power you can get out of the gas, and you also run the very real risk of damaging your engine. Expensive damage. Hole in the pistons damage.

Said differently, you’ll actually get more power out o the 91 octane because your engine won’t run right on 87 octane…and may just self-destruct.

Do yourself a favor. Use 91 or better.

“I wouldn’t want to be the next guy to own that car”

In my town (Wash. DC) there are lots of shabby second hand luxury cars.
They make squeaks and other strange noises, tires visibly out of alignment.

p.s., he asked about 89, not 87

Nothing makes me more angry than for a person to use a lower octane gas in a car that requires premium. I like to run my old Oldsmobile on higher octane gasoline because I jumped the timing up for better performance. I siphon gasoline from cars that I know require premium fuel. When I have gone to the trouble of siphoning fuel from a car that requires premium and the cheap skate owner has used a lower octane gasoline, and my engine starts to ping, it really makes me see red. I don’t want to destroy my engine just because you don’t care about your engine.
Seriously, in the old days, I used to set up my timing and use premium gasoline. I got better mileage and performance and the improved mileage made up the difference in cost. I know that one can’t adjust the timing in modern cars–this is done with the computer. I would guess, however, that the improved mileage using the higher octane on a car that requires the higher octane fuel will justify the added cost.

To BladeCutter:

Did you know this 535i engine does not come with a oil dipstick? So much critical info comes from reviewing the oil on its stick. I have only to rely on computer sensors to update me. Did you also know the mfg recommends a 15K oil change interval? Who in their right mind would go that far on a turbo engine? But maybe I’m wrong.

A cheap person does not care enough about h/er BMW to ask all these small, endless questions in order to develop the expertise that can only be garnered from experienced people who graciously and selflessly pen on forums.

I have a 1998 2.3CL with 325K miles Acura for sale that still gets peoples’ attention and still going strong if you would dare…

Actually, the Acura brings more pleasure because I do not have to worry about inadvertently over-filling the gas (heaven-forbid!) and triggering an emission light, or what my RF-tires are driving over ever second as I am driving the Bimmer. Getting to know my BMW is like walking on egg-shells.

I have a turbo engine in my car and the owner’s manual says 91+ octane recommended and it, too, doesn’t specify synthetic oil, though it does give me a time index for oil changes as well as mileage(my car would be 10 years old before I put 15k miles on it).

While it’s not as fancy or expensive as the 5 series, I did pay a pretty penny for it($34k) and have always used premium fuel and full synthetic oil for it’s oil changes. Do I have to? No, but oil and fuel are cheap, engines and turbos aren’t

Thanks for confirming, bscar.

Stick to the rules with this BMW engine and change its oil every 5K miles!

Why don’t you extend the oil change cycle to 7500 to 10,000 miles and use the money you save to buy premium gasoline?

I don’t believe most people would agree on 10K miles per oil change?

But BMW recommends 15,000 miles. You are cutting the change interval by 33%. Note, too, that BMW has a huge oil sump compared to other cars. That means the oil is cycled less frequently in you rBimmer than another car.

How is the new turbo design cooled during operation? Is it much better than the older design?