It’s not just the frozen toes and icy temps that can get ya down at this time of the year. It’s filling up at the pump too. Yet even if you drive a hybrid—and love its "feel good fuel mileage," they also take a hit in fuel economy when the mercury dips.
Why does hybrid fuel economy drop in winter weather? Well, not only do hybrids suffer many of the same cold weather fuel economy losses of a conventional vehicle, but the hybrid electrical systems lose efficiency too--which equates to a drop in mileage.
Hybrid System Temperature – Just like the vehicle's internal combustion engine, its hybrid system components (especially the battery) work best when they are warm. The onboard hybrid battery depends upon a chemical reaction to both release energy to the electric drive motor and accept charge during regenerative braking. This reaction is severely hampered when the battery is cold, so the engine runs longer and more frequently to make up the deficit while the battery warms up.
Passenger Compartment Heat - Hybrids, just like conventional cars, rely on hot engine coolant circulating through the heater core (heat exchanger) to keep the cabin warm. Obviously the engine needs to run more frequently to keep up with heater demand. The higher the heater setting, the longer the engine runs.
Heavy Defroster Use - Running the defroster can also pull down mileage. When the defroster is on, not only is it dispensing heat from the heater core, but it also runs the AC compressor to remove moisture from the air. Though it's good for the compressor to run periodic cycles in the colder weather (to preserve the integrity of the internal seals), excessive use does reduce fuel economy. In most hybrids, the compressor is run by its own electric motor instead of a belt from the engine, but this doesn't allow the compressor to run penalty-free. That extra electric discharge will require more frequent recharging of the hybrid battery. Running the compressor does hurt fuel mileage.
The following two points hybrids share with conventional vehicles:
Unburned Fuel – Gasoline just doesn’t atomize and burn as well in a cold engine—tiny droplets of unburned fuel remaining in the cylinder are evacuated with the exhaust. That unburned fuel tallies up to a loss in power—using more fuel to go the same distance—not to mention, substantially increasing the your engine's emissions.
Tire Pressure Drops – It’s just a law of physics. Colder temperatures cause the pressure in those tires to drop, about 1 to 2 psi for each 10 degrees in temperature drop. Low tire pressure creates extra rolling resistance and friction, and hence, lost fuel economy.
How to Improve Hybrid Fuel Mileage
- Watch that Thermostat - Just as you'd turn down the heat in your house to save fuel, set the vehicle's heater to the lowest comfortable level.
- Heat the Seats - If your hybrid has them, take advantage of the electrically-heated seats. The heat from the seats keeps you comfy and reduces the need to heat the whole cabin.
- Beat the Defroster Penalty - Setting the heater in defrost mode is the easiest way to quickly clear heavily frosted windows (especially the windshield). However, once the cabin is warm and the windows are clear, turn the defroster off--in most cases, cabin heat will keep the windows fairly frost-free. Turn on the defroster and cycle only as needed.
- Garage It – If it’s available, use it. Even if it entails giving that extra junk to the local thrift shop first, parking your vehicle in a garage will keep it warmer--and that means a shorter warm-up to reach optimum operating temperature.
- Get Your Act Together – Yes, organizing and pre-planning your errands will maximize your time and fuel, since a warmed up car utilizes fuel more efficiently—in addition to making the most of your time as well.
- Ease Up With the Lead Foot – With black ice and slushy roadways a wintertime reality, not only is it safer to go easier on the accelerator, it’s a smart (and easy) way to save fuel.
- Check That Tire Pressure - Keep those tires inflated at (or even a bit above) the recommended range. Many manufacturers' recommendations for tire pressure are suited for ride comfort, while forsaking fuel economy. We usually run our tires several pounds higher for an extra bit of economy.