AutoTips MPG drop in winter tips
Gas milage dropping with the cold weather more than expected?
A few possible causes:
Thermostat: If your heater is also warming up slower than you expected, check your thermostat. If is opening too early, and the engine is not heating up to the proper temperature, the computer in most of the newer vehicles may be running the fuel mixture too rich. It will be delivering more fuel to help with a cold engine. It may be time for a new thermostat, check your owners manual or service manual for the proper thermostat temperature. Thermostats are rated for different temperatures, the engine computer is calibrated to run with a specific temperature. If you go above or below the proper rating, the engine may not run at peak performance.
Air or Coolant sensor: Most newer cars have an air and / or coolant sensor (see also the AutoTips sensor page) for the computer to determine the correct fuel / air ratio for the engine, engine timing, etc. If one of these sensors is bad, the computer can be supplying an incorrect fuel mixture for the temperature. Good references to learn how to check the computer for error codes on these sensors are the factory service manuals, aftermarket manuals, or the "SURE YOU CAN Work on Electronic Ignition" by Wells Mfg. Corp. This is a good reference in a small book that can be carried in the car.
Headlights on longer times: Headlights draw current which the alternator has to make up, and this puts additional load on the engine. It may not be a lot, but is does cost some mpg.
Warm up engine times: If you let your car warm up, in the winter the engine will run richer until it warms up, costing extra fuel.
Other factors: The fuel does not vaporize as well in the cold, and the computer will run the engine richer until it is warm, using more fuel. Headlights are often on for longer hours of the day, the load on the alternator uses additional fuel.
Return to Tips page Return to AutoTips home page.