I agree with twice. I have a BMW 5 series and use regular in it and have for 3 years. The dealer said it would do no harm and using it I still have more than adequate acceleration and get better than epa mileage in both city and highway driving. I Wrote Bimmer Magazine about this problem and got the following response.
These were my questions:
1. Aside from the loss of performance what if any is the downside of using 87 Octane on the 530?
2. Are you aware of any information from BMW of NA on this topic?
3. May I pass your answer to others via Internet forums?
Thank you for your time,
XXXXXX
Hello XXX,
Thank you for your interest in Bimmer.
1. Most BMW produced from about 1992-on and all produced from 1994-on employ knock sensing ignition systems. Knock sensors detect detonation, aka knocking or pinging, caused by low octane gasoline, and signal the engine management computer to retard ignition timing. Retarding ignition timing reduces or eliminates the detonation. This is one reason contemporary BMW engines are able have such high compression ratios.
Retarding ignition timing will also reduce power output. The degree of power reduction depends on the degree of timing retardation.
The knock sensing system has operational parameters. You can only go so low with octane, before you exceed the operational parameters of the system and the engine will experience detonation.
The operational parameters of the knock sensing system are rolled forward as the engine matures, due to carbon buildup on the tops of the pistons.
Lower octane gasoline does not always have the same level of detergency as higher octane gasoline, although detergency is blind to octane chemically. The oil companies just tend to use better additive packages in the pricier fuel. So if you are using low octane gasoline, it would be a good idea to use a gasoline additive periodically. I use and recommend BG44K, BMW Gasoline Additive, Chevron Techron, and Red Line SI-1. The Red Line product is the most economical, because it is highly concentrated. One bottle treasts 120 gallons of fuel.
Automatic transmission BMWs running low octane gasoline will retard timing abruptly when starting out from a standing stop in Drive. This is due to the faster clutching action of an automatic transmission; the same thing happens with a manual gearbox but not abruptly unless it's a holeshot launch. Automatic drivers may perceive this as an ignition miss or hesitation, but it is just normal vehicle function with low octane fuel and an automatic transmission. This is because the engine experiences detonation the second the throttle is opened, and with an automatic the car is under power the second the throttle is opened. The ECU immediately retards timing to address the detonation. With a manual gearbox, everything happens a little more gradually.
2. No.
3. Sure.
Best regards,
Mike Miller
Today
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