If the vehicle has the 2.2L L4 engine (VIN Code 5), use regular unleaded gasoline with a posted octane rating of 87 or higher. If the octane rating is less than 87, an audible knocking noise, commonly referred to as spark knock, might be heard when driving. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. If heavy knocking is heard when using gasoline rated at 87 octane or higher, the engine needs service.
If the vehicle has the 2.0L L4 engine (VIN Code X), use premium unleaded gasoline with a posted octane rating of 91 or higher. You can also use regular unleaded gasoline rated at 87 octane or higher, but the vehicle's acceleration could be slightly reduced, and a slight audible knocking noise, commonly referred to as spark knock, might be heard. If the octane is less than 87, you might notice a heavy knocking noise when you drive.
If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you could damage the engine. If heavy knocking is heard when using gasoline rated at 87 octane or higher, the engine needs service.
Chevrolet Cobalt Owners Manual. Engine Compartment Overview
When you open the hood on the 2.2L L4 engine, here is what you will see:
A. Engine Air Cleaner/Filter (2.0L Turbo Engine) or Engine Air Cleaner/Filter
(2.2L Engine).
B. Engine Oil Fill Cap. See “When to Add Engine Oil”
under Engine Oil.
C. Engine Oil Dipstick (Out of View). See “Checkin ...