Every winter, the same story. Owners come in worried because their fuel consumption has gone up. Most of the time it is a completely normal thing. But to tell normal from a fault, you need to understand why a car uses more fuel in winter.
A Cold Engine Burns More Fuel
This is the main reason consumption goes up in winter. When you start a cold engine, the computer injects more fuel than usual because a cold engine needs a richer mixture to run smoothly. Until the engine reaches operating temperature (usually 80 to 90 degrees Celsius), consumption is significantly higher.
In summer, the engine warms up in 5 to 7 minutes. In winter, especially on short trips, the engine may never reach optimal temperature. If your daily drive takes 10 minutes, the engine spends most of that time in the warm-up phase, which is the phase with the highest consumption.
Short Trips Are the Enemy of Fuel Economy
If you only drive short distances in winter, to work, to school, to the store, the car never gets up to temperature. The engine burns more, the oil never gets warm enough to evaporate condensation, and the battery never fully charges. Consumption on those kinds of trips can be double the normal rate.
Tip: If you can, take the car on a longer drive of 20 to 30 minutes at least once a week. That is good not only for consumption but for overall engine health.
Winter Fuel
The fuels sold in winter have a different composition than summer blends. Winter diesel contains additives that prevent freezing, and winter gasoline has higher volatility for easier cold starts. Both of these properties come at a cost: slightly lower energy content per liter. The difference is not dramatic, but it adds to the overall increase in consumption.
Heating and Defrosting
Cabin heating on diesel vehicles does not significantly affect consumption because it uses engine heat. But the rear window defroster, heated seats, and the blower on full power all load the alternator, which loads the engine, which burns more fuel. On gasoline engines, the effect is a bit more noticeable.
Air conditioning, if used for defrosting the windows (which is an effective method), also increases consumption because the A/C compressor draws engine power.
Winter Tires Have Higher Rolling Resistance
Winter tires are softer and have a more aggressive tread pattern than summer tires. That gives them better grip on cold and wet surfaces, but it increases rolling resistance. The result is higher fuel consumption, typically 3 to 5 percent more than with summer tires.
Idling to Warm Up Does Not Help
Many drivers have a habit of starting the car and letting it idle for 10 to 15 minutes before leaving. On modern engines, this is unnecessary and counterproductive. The engine warms up faster under light load than at idle. Half a minute of idling after startup is enough, then pull away gently and drive calmly until the engine reaches temperature. Long idle warm-ups only waste fuel and burden the DPF filter on diesel engines.
How Much Extra Is Normal
Based on our experience, a normal winter increase in consumption is between 10 and 20 percent. If you use 6 liters per 100 km in summer, 6.5 to 7 liters in winter is perfectly normal. If the difference is more than 25 to 30 percent, or if consumption has jumped suddenly, then you may have a fault that happens to coincide with winter.
The most common culprits for abnormal winter consumption are: a thermostat stuck in the open position, a faulty engine temperature sensor, or a problem with the glow plugs on a diesel engine.
When to Suspect a Fault
If the engine temperature never reaches the normal mark on the gauge or the cabin heating barely works, you probably have a thermostat issue. If the engine runs rough for a long time after startup, check the glow plugs and temperature sensor. All of these are relatively inexpensive repairs.
If your winter fuel consumption seems excessive, get in touch so we can check. Sometimes replacing a thermostat that costs 20 KM saves you hundreds in fuel over the course of a winter.