2008 PT Cruiser - oil issues

If they burned oil you'd see blue smoke from the exhaust. Start by looking for external leaks. Years ago the common teaching was synthetic oil was "cohesive to itself", meaning if there was a leak, the leaking oil would suck more out behind it until the engine was empty.

One test is to add a small bottle of dye to the oil, then drive it long enough for the level to go down. Search with a black light. The dye will show up as a bright yellow stain that you follow to the source of the leak. Also check the tail pipe.