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.
This is assuming there’s no active knock sensing and timing control, which is unlikely on anything made in the last 15-20 years, especially if it requires premium. The manufacturers learned that people are often stupid, and mistakes happen. So a tank of low grade here or there can be accounted for. But if you use it constantly while beating on the engine, yeah, damage will add up over time if you exit the bounds of what the computer can adjust for.
The computer can either adjust for it or it can’t. Knock sensors have been in cars for much longer then that. Once again knocking is the fuel igniting before spark and after spark. You can still have ignition events occur after spark has occurred.
Use the right fuel period.