My boyfriend's truck has started using a lot more gas than normal. Could it be caused by the weather becoming colder? Or are there any other things that could be causing this? There's nothing going wrong with the truck and nothing that has recently gone wrong with it. Other than needing a new serpentine belt. Any suggestions? Thanks!

Check tire pressure

Colder temps mean the engine is in enrichment longer. (like the old days of a choke)
Engines burn less efficiant until they are fully warmed up.
Winter blends of fuel now at the pumps are good for cold weather, but suck for gas milage.

I once had a brake caliper sticking and it cost me about 5 miles to the gallon for a few tanks until I found it. Good luck

Tips to Improve Gas Mileage

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.