re: #946 KenJen

Its a 1997 Mercedes E320.

According to the site I checked (rockauto.com), it has two knock sensors (one per cylinder bank), so I think you’d be okay trying regular.

Do you check the gas mileage regularly? I mean, not using a trip computer, but doing it the old fashioned way, making a note of the odometer at each fillup, or resetting a trip odometer each time? If you do, then let the tank run pretty low, then fill it up with regular. Drive it the way you normally do, at least 150 miles (that the minimum to get a valid mileage reading), and check the mileage.

What you’re looking for is whether the savings of switching to regular is offset by the drop in fuel mileage, due to the knock sensors backing off the ignition timing. My guess is the mileage won’t drop that much. Performance (like getting on highway ramps) might suffer a little bit, though. And cars tend to need a little more octane in summer, because of the hot temperatures.