This is most interesting. I just got my X3 and have used top tier gas in the highest octane they offer here in Northern California which is 91. I'm always jealous when I hear about the 93 octane that is available in other locales. That being said, I owned Saabs previous to this new ride and always used 89 with no apparent difference in performance or gas mileage. I drive a lot with my own car for my job (400+ miles weekly) and so I am considering trying 89 in my X3. I will be happy to report back on any changes noted, now that I'm confident from the material in this thread that it will not cause harm to the engine.
I has run through 3 tanks of mid grade fuel "89" in the X3 and have observed no change in performance or gas mileage. I average about 18.5 in mixed driving with a lot of short trips in town.
Had G500 & G55 in my garage. 14.7 the best MPG I've seen by far. Always used 91 or higher(when available). Did someone say fuel savings.... oh wait... Great point guys!
There was a number of people at MB forums wondering about the same thing. Huge discussion! You might be surprised but in some extreme situations or with no other options around some guys even used 87 to fill up AMG cars. No performance issues reported! However everybody agreed that due to supercharged engines you should use higher grade fuel on regular basis for obvious reasons. You may go 87 once in a while but that's just gonna save you a couple of bucks. If you can't afford couple more dollars to get recommended fuel perhaps you should consider driving less expensive vehicle or a hybrid. That's what everybody agreed on as well. 2 Cents from me.
Good modern cars have knock sensors constantly monitoring the engine and those sensors feed info back to the DME control unit to retard spark and reduce power when detonation is detected. When lower octane fuel is used, the engine develops less power, but still has plenty to get the ordinary jobs done. Often the difference is not detectable---freeway driving for example is low stress and the engine doesn't need that much octane. It is said that premium fuels have more detergents than regular, so a steady diet of regular seems to result in dirty injectors. My Ford Raptor is listed by the factory at 410hp with 93 octane and 400 hp with 87 octane. I think that's right. I can't feel any difference.
Thanks for great input! I personally think this THREAD should be divided in two parts: 1st Using Low Grade fuels from technical point of view as a concept. 2nd Fuel Saving / Economy related issues. As for the mechanical/technical point of view the most important part has already been covered here, fuel saving is a totally different aspect. If you are not happy with your MPG there are few things to consider that could save more money than buying low grade fuels. First Tip. From my own experience with 2008, 750li(360bhp, V8) I was able to get 25-28MPG on hwy really easy! Perhaps some BMW owners have no clue that cruise control lever works almost as good as accelerator pedal(even accelerates really hard when pushed all the way). Don't hesitate to use it when you are not in the mood for aggressive driving and watch your MPG go up! Even with TwinTurbo V8, I am able to get a little over 24MPG on hwy in cruising mode! Is that really bad? Not at all. Second Tip. If you are really into fuel saving and drive less than 50 miles a day then the best alternative would be to buy an electric car. I have several friends who just drive from home to work and buy some groceries(mostly in the city). They are really interested in getting those because you don't really need gas here unless you plan a longer trip. Third Tip. Look for food stores that offer discount points that you can use at your local gas stations. There are things we all buy on regular basis like food, drinks, etc. We buy those things anyway so why not to get something in return? In Florida some food stores started to practice this already and I was able to purchase 91gas at $3.30 a gallon price. Compared to $4.15-$4.20 gallon prices here in New Your City that was really something!
Do you really think your car will last longer using a higher octane fuel? My recommendation is frequent oil filter changes, not necessarily frequent oil changes. And take care of the little problems before they become big ones. I too plan on driving my cars into the ground. When it comes to fuel. Top Tier, high volume stations. And don't get fuel while a station is getting a delivery.
Some fun conjecture for the group form a friend at Chevron: 1) Their gas has the same level of detergents across grades. 2) The evaluation method for octane hasn't been revised in decades and it's not accurate. You actually get higher octane than what's stated. 3) You get for what you pay. Cheap gas is the stuff the major players won't take because it's been in the tanker too long or the contents aren't up to snuff, i.e. sulphur levels etc. It may be OK per government regulations, but it doesn't meet their requirements. The cheap gas brands (any grocery store, Earl's Schieb etc.) buy it at a lower cost and sell it for less. It also won't have the detergent package you get in a name brand gas. 4) I'm told most people don't need high octane and we can use lower octane just fine. From outside Chevron: 5) Their Techron additive is highly effective at breaking up carbon deposits. I dump a couple bottles in every so often even running Chevron regularly. Seafoam also works well. 6) Shell's Nitrogen enriched tagline is manure. I don't know which marketing twit thought of it, but from a thermodynamics standpoint, the last thing you want in a combustion process is an inert gas that absorbs heat. It's likely a nitrogen containing compound that is part of their detergent package. I had heard that they were buying Techron under license to use as their V-Power. I am not sure if the new tagline signals a change in formulation. I can agree with 1-3. For number 4, I notice a MPG decrease using 87 vs. 89 or 91. I'm still running tanks of 89 and 91 back to back to see if there is a difference in MPG. In terms of power, it's hard to tell without a dyno, but I bet the ignition timing is retarded running 89 vs. 91 or 93 (not available in CA it seems).
on my 328 i have check the ignition timing with scan tools and changed octanes 89 vs 93 over several tanks i see absolute no difference with 89 as related to timing reduction.
I just found this thread, know it's pretty old, but I have some relevant date to add to the discussion. I just traded off our '08 535i with 138,000 miles on it, and I maintained it per Mike Miller's Old School maintenance schedule. The car ran flawlessly, had great power, and on the highway returned 27-28 mpg consistently. It had 47,000 miles on it when I purchased it and I got ans oil change, set of brake pads and spark plugs, and a HPFP replacement before the warranty ran out. After that I did all the service work myself. I started using 87 octane E10 about 3 years ago and that is pretty much all it had except a couple of experiments with 93 just to see if anything changed. It did not. Mileage was the same, performance was (seat of the pants) the same, so I reverted back to 87. A little background. I retired in 2006 from a 37 year career in the oil business, running a family owned oil distributorship selling Exxon, Citgo, Unocal and Conoco gasolines. Anyone who says the cheap stations sell inferior gasoline are misinformed. Except for the additive package which is injected into the tanker truck when the fuel is loaded, it all comes out of the same tank. The big oil companies like Exxon, Chevron, Shell, et al have pretty much sold off their terminals and they just ship product to the terminals where they lease space. Their proprietary add pack is kept separate but otherwise the gas is the same. All Grades of gas contain the same level of detergents, it is a myth that 91-93 has more. Now yes, the add packs contain some things the regular gas does not, like Chevron's Techron, but otherwise its the same. I respect the Top Tier rating system but it is not the be all and end all of gasolines, and usually won't make much difference. Case in point is my 535i with 138,000 miles, running on whichever gas was the cheapest available. The way to get crappy gas is to buy from a small station that sells very little and doesn't get regular deliveries. Busy stations get frequent tanker drops and thus keep fresh gas. Octane does degrade over time, even if the temperature changes very little in underground tanks. So, what do you do? If it makes you feel better to pay 40-60 cents more per gallon for premium, go ahead, but it is mostly false economy. I certainly believe my 535i ran with the ignition timing slightly retarded due to running 87 instead of 89 or 91-93, but it was unnoticeable to me.
