Quote:
Originally Posted by Kromans1
I'm getting my first BMW soon and I was wondering, what happens to a BMW engine when you put regular gas into it?
I won't be doing this, of course, but I'm just curious.
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You're going to be getting many types of responses to this, some of it misinformation. Seeing that you're in the US, I'll share what applies in the US. I'm unfamiliar with other countries fuel regulations.
Many believe premium fuel has more or better additives than regular. NOT TRUE! There may be some rare exceptions for boutique premium blends but regulations ensure all fuel sold in the US has a minimum amount of additives. In most cases regular gas has the same amount as premium in a particular brand. Another specification (not regulation) is "Top Tier". "The additive companies create additive formulations and conduct testing, ultimately receiving TOP TIER™ approval.
The fuel retailer licensee agrees to purchase fuel treated with a TOP TIER™ additive at the correct concentration and display the logo." Read more at
https://toptiergas.com/.
Most major vehicle manufacturers recommend (but don't require) Top Tier fuel.
So… if most fuel brands include the same additives in all of their fuel, what is the difference between regular, mid grade, and premium? OCTANE
Contrary to popular belief, premium is not more powerful than regular gas. Premium is formulated to reduce pre combustion ((when the fuel combusts before it's supposed to (it's suppose to combust when the spark plug fires)). The octane number is the measurement of the fuel's tendency to precombust. The lower the number, the easier it is to combust (at lower temperatures and/or compression levels).
Recommended octane levels vary by vehicle. On my G29 Z4, minimum is 89 and recommended is 91. What happens if I use regular (87 octane)? I'm likely to get more precombustion (synonymous with preignition), especially at higher temperatures and under greater load (accelerating or going uphill for example). Over time, excessive pre combustion can cause damage and/or premature wear to the engine components (precombustion generates forces against the piston before it's reached the top of its stroke), decreasing engine longevity.
Most or all modern vehicles have technology that can identify precombustion. They differ in how well they handle it. Many will adjust the ignition timing (and perhaps air/fuel ratios) to effectively compensate, resulting in reduced engine performance but minimizing any damage to the engine. Some vehicles don't manage it as well as others. I can't tell you specifically how BMW vehicles manage it because it's proprietary information.
Bottom line: Try to use the minimum octane recommended by the manufacturer (in the manual and near your gas cap). If on rare occasion you only have access to regular 87 octane gas, it'll be perfectly fine to use it as long as you don't put the engine under heavy load (high temperatures, towing, long uphill climbs, etc.) Fill it up with the recommended octane at the next opportunity.