What type of fuel should a BMW 5 Series 525 use?
2 Answers
BMW 5 Series 525 uses 95-octane gasoline. The gasoline octane rating represents the ratio of the actual gasoline's anti-knock performance to that of standard gasoline. The higher the octane number, the stronger the anti-knock performance. 92-octane gasoline: 92-octane gasoline contains 92% isooctane and 8% n-heptane. Standard gasoline is composed of isooctane and n-heptane. A higher octane number is not necessarily better; the appropriate gasoline octane should be selected based on the engine's compression ratio. 95-octane gasoline: 95-octane gasoline contains 95% isooctane and 5% n-heptane. When the engine's cylinders perform piston movements, gasoline and air mix and compress inside the cylinder. If the pressure is too high, knocking can occur.
I've been driving this 525 for almost three years now, and I always fill it up with 95-octane gasoline as clearly required in the BMW manual. Actually, 98-octane gasoline can also be used—it burns more efficiently and can slightly boost performance, but it's significantly more expensive. Once, I had to use 92-octane in an emergency, and the engine started shaking noticeably, even triggering the check engine light. I was so scared that I rushed to the 4S shop to have the fuel system cleaned. The mechanic told me that using the wrong octane once in a while isn't a big deal, but long-term use of lower-octane fuel can damage the high-pressure fuel pump and injectors, and the repair costs later on would far exceed the savings on fuel.
