Should I Use Premium Fuel?

I recently purchased a 2004 BMW X5. The handbook says I should use 91 octane fuel, but this is much more expensive. Will I damange anything if I use 87 octane fuel? I have heard that acceleration is compromised but that really doesn’t matter to me. But I definitely do not want to damage he engine.


Review your owner’s manual wording. Does it say “Must” or does it say “Recommended”. There is your answer. “Should” is equivalent to “Recommended”.

You have a high end car. Expect to use premium fuel. It boggles my mind that people will go out and spend $40k+ on a luxury car yet piss and moan when they have to use premium fuel. Amazing.

Premium isn’t “much more expensive” than regular. Look again. There is only about a 5% difference. If you recently purchased the vehicle, you knew what you were getting into, or at least you should have.

This has been discussed to death here over the past few months. Everybody comes back to the same advice: Read the owner’s manual.

I’m usually one that says try regular, but BMWs are built with engines that benefit more than most from premium. You’ll probably be dollars ahead, once you add in the mileage benefits.

You can afford an X5 (well, maybe), but you’re not willing to pay for the fuel it needs? Didn’t you know it needed premium before you bought it? If not, why not?

I hear a little bird singing, “Cheap, cheap, cheap.”

This is a good reason NOT to buy a used BMW. How many other penny-pinching owners of the ultimate driving machine have fed them regular instead of the premium they need? That’s a rhetorical question.

My girlfriend purchased a 2000 Land Rover Discover V-8 a couple of years ago. It was meant to burn the 91 octane. She was of course using ethanol blended gas and getting 12 to 14 mpg. I finally conviced her to switch to gasoline which improved the mpg. On a 1000 mile trip to VA we tested different octanes of gasolines. I think we started with the 87 octane regular, then to the 89 octane, to 91 octane and figured the mpg with each tank. The SUV didn’t like the 87 octane and preferred the 89 or 91. The mpg with the 89 octane was about 17.5 and the 91 about 18.2 mpg. So after the trip we decided based on our on the road research to settle on the 89 octane even her manual recommended the higher 91 octane. She has since gotten rid of the SUV… She owed $8,000 and was lucky she got $5,000.
On your car, I would change the fuel filter and get a tune up. Use only GASOLINE in it and do your own testing of different octanes, particularly the 89 and 91 octane. In your testing, keep records of your mpg and performance. That way in 1 or 2 months you can report your findings back to us. Hope this helps.

I have to ask What are you implying when you advise "use only GASOLINE in it? Are you posting from the States?

Keep in mind that there is a difference in regular and high octane (I hate calling it premium as it is not better than, but rather different than regular.) In your car using regular will reduce performance and it will also reduce mileage . Chances are you will save very little if anything by switching to regular, it might even cost you more per mile.

“Use only GASOLINE in it”

As opposed to using what?

If you mean that one should avoid the use of E85, then I agree, especially if the vehicle was not designed to run on E85. Serious damage can result from the use of E85 in vehicles not designed for it. If you mean that one should avoid the use of gasoline blended with lesser amounts of ethanol, that is virtually impossible to do nowadays as E10 is becoming ubiquitous.

Joseph Meehan raises a valid but often overlooked point. The money you save at the pump to use regular may cost you more than you realize.

The difference in price between 89 and 93 octane is about 6.5%. If your mileage drops by more than 6.5% when you use regular, your switch to regular just cost you money. On a car that gets 20 miles/gallon, all it takes is a drop of 1.3 mpg for the switch to regular to cost you money.

The key takeaway is: Any switch to regular (assuming the owner’s manual allows for it), should be accompanied by monitoring your MPG so you know if you’re saving or losing money.

If you have the six cyl in the X5, then you have the same engine as my wife’s 2004 330. Our experience is that the the extra 1.5 mpg we pick up using premium offsets the cost difference. Also, the car runs perceptively smoother on premium. After observing these two facts, we settled on premium for good. Also, we run almost exclusively Chevron gasoline, which costs a few cents more than the bargain brands, but Techron is about the best additive on the market for keeping injectors clean, according to independent tests.

What I’m recommending is that you avoid using anything with ethanol in it. The savings in mileage alone
will more than save the added expense of using the mid 89 octane or even the 91 octane. Yes, I’m the states, Alabama,USA to be exact. Around here, Shell seems to be holding out longer the others and selling GASOLINE. I know where several stations that sell the “good gas” and use them. Please remember that ETHANOL was developed when we had vehicles with carburators…it mixed with the gas, burned and everything was hunky dorie. That changed when computers and injectors entered the picture.
If you have a mpg difference of 4 between the two types of fuel (gas and ethanol) and a 20 gallon tank,
you’ll save about $16.00 per 20 gallon tank by seeking out the stations selling GASOLINE.
Try it you’ll like it, plus your cars performance improves as well. It a win/win solution.

My opinion is often at odds with the majority it seems but here it is anyway. I don’t think there is a one size fits all when it comes to this.
Every car is different and that includes cars of the same year and make.
One car may run like garbage or suffer problems from using low octane fuel and another may be perfectly fine.

It is recommended that 91 be used on my Lincoln but it’s been running fine with no loss of power, mileage, etc. nor does it suffer from the most critical thing of all - pinging. It’s been using 87 for about 140k miles now with zero problems and regular inspection of the spark plugs (the best evidence you can find) shows absolute normalcy.

So my advice is that it depends. If the car does not ping or suffer mileage losses then you will not likely have any problems.

While you’re at it, do a net search and read how octane is figured. 87 octane in Europe is 91 in the U.S. It depends on the method of figuring and this was even true with Avgas in WWII. 100 octane in the U.S. was something like 130 octane in Germany. Same gas - just a different way of looking at it.

For the record, I’m on the road right now in Colorado, my Lincoln Mark is full of 85 octane and it’s pulling mountains while suffering zero problems and still getting 27.2 MPG; the same as it does on 87 or 91.
The MPG versus speed issue (recently debated somewhat hotly) is something I will start a separate post on when I return home as I am logging in the details on this very closely.

JMHO anyway to use as you see fit.

Here in NH and MA…they all use 10% Ethanol…that includes Shell.

I hate calling it premium as it is not better than, but rather different than regular.)

It’s called MARKETING. The gas stations did that purposely to make you THINK it’s better gas. How many times have posters made statements about Premium being a BETTER gas then regular in this forum. I can’t count the number of times.

While you’re at it, do a net search and read how octane is figured. 87 octane in Europe is 91 in the U.S.

Yea. They are research and manufacturers. As I recall in the US it is a average of the two. The auto manufacturer (be they US or other) list the octane based on what is posted in what country, so in the US all the cars, no matter where they came from, will be using US method of calculating the octane.