octane?

[Geneticfreak]

First time BMW owner, picked up our 2005 X5 last week and love it. Although 91+ gas is recommended! the dealer did say that we would be ok with 89, since 91 isn't a real option. Being a high milage engine, does it make a difference if we go with 89 instead of 93?


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[electricalserv x5]

no no no no no.................which engine? 3.0 4.4 ,4.6is,4.8is? what year?how many miles?

[lhordmclain]

That's the same thing my sales guy told me when the dealership delivered our brand new X5 about 10 years ago

"It's good to use 91+ all the time to get the maximum &optimum engine performance.
BUT you can also use 87 or 89 only when you have to". At that moment I lost my faith in him (sales dude)

** I always pay the extra .40c per gallon and use Shell or BP as much as possible

[motordavid]

There are literally pages of full threads on the topic...OP might use Search Tab for hundreds and hundreds of opins.

Seems to be two camps:
-use nothing but premium, and even pages of debates on 'which brand'
-use premo and occasional 89, brand being besides the point.

My anecdote is: occasional premium, more than occasional ~89, and the 3.0 IL6 hasn't missed a beat in 96k+ miles/almost 13 years.

Run what you choose/like, imo.
GL, mD

[m5james]

If the car says to use it, then you use it. BMW gains nothing for whatever fuel you're using it after the fact, so it's not like it's some conspiracy theory to make more money. I accidentally put 87 into my 740iL and the car fell on it's face...bucked and stumbled, felt like someone dropped an anchor when I went WOT, just didn't run right. The fact is the engine was tuned on higher octane for a reason. Just like you can tell the difference between slim milk and whole, your car can tell the difference between 87 and 91 or higher. I explained it like this to my mother...

It's a BMW, so it's higher compression than her Honda. Higher compression means it's runs hotter. Higher octane fuel burns slower, which means it helps cool the engine for that microsecond before it's burned. Can she run 87 octane, yes. Will the engine run hotter, which means it'll ping more, which means the computer pulls timing to make up for predetonation, which means she'll have less power AND lower gas mileage, yes. She can either pay .40 less per gallon and get 20MPG or she can pay .40 more per gallon and get 24MPG (theoretical numbers), but ultimately you're better off following what the manufacturer suggested because it was made for it.

If it recommended 5w30 oil but WalMart had 15w40 on sale, are you going to put in the wrong oil to save money? It'll cost you in the long run, so pay now or pay later. Choose your poison.

[SMOKEY53]

What he said.

The engineer's only object is to meet the sweet spot between making the car run at optimum performance at lowest cost. If they could achieve that with lower octane fuel, they would.

There is no vested interest in making the car use more expensive fuel - in fact, if they could deliver the right performance and economy characteristics with a lower octane fuel and deliver lower running costs - they would!

With that said, the car does have the ability to retard timing to cope with a lower octane rated fuel. You will be duly rewarded with lower MPG and less performance.

The choice is yours - but my question would be, who buys a BMW and skimps on fuel?

[THE VEIN]

Sooooooooo don't bother with 93 or 94 and just put 91? I was always told that u can run the lowest octane that the engine will allow. So if you're putting 89 and the engine runs the same then u can run 89 all the time

[thrillcat]

Engines are tuned for a certain octane fuel. You can run other fuels, but it won't run as well. You can tune a guitar a half step low, but when you try to play with the band, it's not going to sound right if the rest of the band is tuned standard.

I had the opposite problem years ago with a Chevy Blazer. I thought putting higher octane in it was taking better care of it, but I was having issues with bad acceleration, took it to a garage, and the mechanic asked if I had been putting cheap gas in it. I told him that I'd been running 91 and he said that was my problem. The engine was tuned for 88/89 octane. I started putting the cheap stuff in and didn't have any more problems.

[Ricky Bobby]

Originally Posted by SMOKEY53

The choice is yours - but my question would be, who buys a BMW and skimps on fuel?

Answer:

More than 3/4 of the BMW owners who lease their cars, or who can afford the monthly payments but want to skimp on gas because "super is too expensive".

It's pretty hilarious sometimes because its such a stigma and a negative by some, "ugh I have to put premium in this? whats gonna get hurt if i put regular in it?" , and considering that our gas is such shit nowadays ever since ethanol has wreaked havoc on our fuel supply and our gas tanks, etc, there is a TON wrong with putting regular in, but for the average Joe, they don't care.

Hell, nowadays, not even my Scag, or any of my 2-cycle equipment gets anything less than 93 octane, I'd rather have my equipment for a long time than save a buck or two at the pump.

[Qsilver7]

Depending on which engine you have...the information from the owners manual can be different. As some have stated above, take that information...and the rest is up to you. Do take note of the meaning of "recommended" and "required". Also know that elevation to sea-level, topographical terrain (hills or plains), and temperature can all have an affect on performance or the demand you need from the engine. And the type of driver you are can make a difference as well. If you have a gentle foot or (granny-toe)...your driving demands from the engine is going to be different than those that are lead-footed.

My e30/e32 (m20/m30 engines) only required fuel with an 87 AKI...higher octane fuels would be a waste because it didn't have knock sensors to adjust for different octane.

AKI is the calculation used in the USA to determine octane...RON & MON are used in other parts of the world...and have slightly different numbers due to the way octane rating is calculated. (87 AKI is equivalent to 91 RON)

For my e34, e38 & e39...87 AKI, 89 AKI & 91 AKI is actually mentioned.

(my (e34) 525iT w/M50 VANOS engine recommended 91 AKI w/87 AKI as minimum requirement...my 740iL w/M62 non-VANOS engine recommends 89 AKI w/87 AKI as minimum requirement...my 540iT w/M62TU engine recommended 91 AKI w/87 AKI as minimum requirement)

The fuel specs for my 06 X5 4.4 w/N62 engine gives no other "recommendation" and says that it "requires" 91 AKI: