Old man at the Benz dealership says he’s been driving the same car for a long time and usually only puts in 87 octane in sprinkled with 91 every few times. What problems could this cause? Do I have to put in 91?
Disclaimer: I’ve owned (paid off) the car for 6 years and do put in 91, but trying to cut costs.
Over time, in a high-compression engine (over about 10:1), using a lower octane fuel than it’s engineered for will result in knocking (detonation), formation of hot-spots, and eventual preignition.
In an air-cooled or in a non-interference engine (lower compression, both, usually under 10:1) there is absolutely no benefit to running higher octane fuel.
The higher the octane number, the more tolerant of higher pressures before ignition.