[croush]

I hae a 2005 Ford Focus. I hae always gotten 28-32 mpg. Recently I hae only been getting average of 24 mpg. What can be the cause? Oil changes are done every 3000 miles with no changing in driving. Help!

[envee505]

Have you had a tune up lately? (spark plugs wires) that can have an effect on your gas mileage

[ebaines]

It's not uncommon to see a drop in gas mileage in the winter months, principally because it takes much longer for your engine to reach its optimal operating temperature. Hence your car runs richer longer in the winter until it warms up fully. Also, cold air is denser than warm, which means it takes more molecules of gasoline to react optimally with a liter of air when the air that is cold than when the air is hot - but this also gives you more power output. Hence you may actually be getting more power out of your engine in the winter and not realize it, which in turn means lower mileage. In theory one could lay off the throttle a bit to get the same power output (and the same mileage), but that would be difficult to control in practice.

[TxGreaseMonkey]

Winter weather is the likely culprit. Changing to synthetic engine oil and synthetic transmission fluid will help. Here are some other tips:

1. Check for Diagnostic Trouble Codes.
2. Replace oxygen sensor. A bad oxygen sensor can radically affect gas mileage, since it controls fuel injector duration.
3. Go over the whole ignition system. Replace, for example, spark plugs (with exact brand and plug number that came in the vehicle), spark plug wires, rotor, and distributor cap. Replace platinum plugs at half the recommended mileage.
4. Replace air filter and fuel filter.
5. Check idle rpm and engine timing.
6. Check MAF sensor, if so equipped.
7. Check tire pressure.
8. Add Shell Regane or Chevron Techron fuel injector cleaner to gas tank every 6 months. This will clean fuel injectors, throttle body, valves, and combustion chamber.
9. Use full synthetic lubricants; e.g. engine oil, manual synchromesh transmission fluid, automatic transmission fluid, and differential fluid. This should increase gas mileage by 8 to 10%.
10. Check for dragging brakes, including emergency brake.
11. Check alignment.