there isn't enough info given to justify a clear answer. we are trying to solve a 3 variable question with only 2 known variables.
if OP was driving an avg 100mph for 2 hrs, half a tank is actually exceptionally good (about 50mpg)
now if this 2 hrs drive was at a crawl with an avg speed under 30mph, then it would be horrendous mileage (like under 15mpg)
but generally speaking, here are some common things that can affect mileage:
- extra weight (heavy cargo, passenger, etc)
- drag (i.e. roof mounted accessories, large spoiler)
- low tire pressure
- poor wheel/tire combination (i.e. too large, too heavy, too wide, etc.)
- poor alignment
- low or bad 12V battery (while the 12V battery doesn't run the electric motor, the car will spend a lot more time charging the 12V system vs if you had a good/new battery)
- heavy use of A/C (or always on)
- behind on general engine maintenance (engine oil, air cleaner/filter, spark plugs) and use the correct oil, that is huge.
heavy stop and go traffic is also particularly hard on MPG in the CRZ due to having to start up the engine each time the car moves (no EV mode). so mileage can be very poor in gridlock traffic. even without traffic, driving at very slow speeds burns up gas as the car cannot disengage the gasoline engine except cut out fuel when braking/coasting.
'13 CRZ - PWP EX 6MT