List of 53 causes of poor gas mileage

The gas mileage of a vehicle is the amount of miles that vehicle can travel given an amount of fuel. In other words, it is the ratio of the number of miles travelled to the volume of fuel burned in the course of the travel.

There are numerous causes of high/increased fuel consumption. This can make troubleshooting of bad gas mileage difficult for non-experts.

It is important to know the car manufacturer's specified fuel consumption rating so that the thinking that the car consumes fuel will not be as a result of false perception.



1. Worn spark plugs
2. Leaking injector
3. Vacuum leak
4. Binding brakes
5. Poor alignment and wheel balancing
6. Incorrect wheel/tire size
7. Lazy or faulty oxygen/AF sensor
8. Incorrect cooling fan operation (engine overcooling)
9. Aggressive driving habit
10. Stop and go driving
11. Restricted exhaust or exhaust with excessive flow
12. Worn fuel pump
13. Bad fuel pressure regulator
14. Faulty ignition coil
15. Incorrect engine timing
16. Faulty PCV

17. Faulty or dirty MAF/MAP sensor
18. Incorrect engine oil viscosity
19. Extra weight in the car
20. Using lower octane rated fuel in contrast with the recommended octane rating
21. Absence of cooling system thermostat
22. Stiff engine parts like pulleys and belts, air conditioner compressor.
23. Fuel line leakage
24. Incorrect tire pressure
25. Using the wrong gear
26. Faulty engine coolant temperature sensor
27. EGR valve leak
28. Dirty air filter
29. Dirty fuel filter
30. Low engine compression
31. Slipping clutch or transmission
32. Poor aerodynamics
33. Bad fuel
34. Clogged injector
35. Degraded engine oil
36. Fast driving
37. Air conditioner use and air conditioner that is overworked
38. Rolling windows down at top speeds
39. Excessive idling
40. Faulty knock sensor
41. Faulty camshaft sensor
42. Faulty variable timing sensor

43. Cold weather 
44. Low traction roads 
45. Faulty vehicle traction control system 
46. Excessive/unnecessary braking 
47. Electrical accessories like high power amplifier, inverters or extra lights 
48. New vehicle break in 
49. Open loop operation of the engine management system 
50. Worn tires 
51. Carbon build up 
52. Tailgating other drivers causing frequent use of brakes or being in a position where the air pressure created by the vehicle at the front is a disadvantage.

53. Wrong engine timing.