As soon as temperatures drop below zero, the calls start. "My consumption went up by two litres, what is wrong?" In most cases nothing is wrong. Winter driving simply costs more fuel than summer driving, and the increase is the combined result of several factors acting at the same time. We explain the same things at our workshop every winter, so here they are in one place.
Rich Mixture During Cold Start
This is by far the most important factor. When you start a cold engine, the ECU injects significantly more fuel than normal because cold cylinders, the intake manifold and the exhaust system do not vaporise fuel efficiently. The engine runs on a richer mixture until it reaches operating temperature of 80 to 90 degrees Celsius.
In summer the engine warms up in five to seven minutes of gentle driving. In winter, at minus ten, that takes roughly twice as long. If your daily commute is short, say ten minutes to the office, the engine spends almost the entire trip in the enrichment phase. On those trips, consumption can be 30 to 50 percent higher than on a warm engine. For city drivers who only make short trips, this is the dominant cause of increased winter fuel use.
That is why it pays to take the car on a longer drive of about twenty minutes at least once a week. The engine reaches full operating temperature, the oil evaporates condensation, the battery charges properly and the DPF filter on diesel engines can run a regeneration cycle.
Thick Oil, Cold Transmission and Extra Friction
Engine oil at minus fifteen has several times the viscosity it has at operating temperature. Until it warms up, the crankshaft, pistons and valve train work against the resistance of thick oil. The same principle applies to gearbox oil, differential fluid and wheel bearing grease. All of these mechanical resistances draw engine power, and every kilowatt spent overcoming friction means more fuel burned.
Choosing the right oil viscosity for winter conditions helps. If your recommended specification allows a switch to a thinner winter-grade oil, that step saves fuel and makes cold starts easier. We cover the full winter preparation checklist in our guide on how to prepare your car for winter.
Idling to Warm Up, a Habit That Only Wastes Fuel
Many drivers start the engine and let it idle for ten or fifteen minutes before setting off. On modern engines this is counterproductive. An engine at idle produces minimal heat and warms up very slowly. Under light load, in other words driving gently at low revs, it warms up two to three times faster.
The practice is simple. Thirty seconds to one minute after starting, pull away gently and drive calmly until the engine is warm. No hard acceleration, no high revs. The engine warms up sooner, less fuel is wasted, and the neighbours are not listening to an idling engine at seven in the morning. On diesel engines, prolonged idling also burdens the DPF filter because low exhaust gas temperatures prevent regeneration.
Winter Tires and Air Pressure
Winter tires have a softer rubber compound and a more aggressive tread pattern that provides grip on snow and ice. The price of that grip is higher rolling resistance, typically 3 to 5 percent more fuel compared to summer tires on dry road.
An often overlooked factor is tire pressure. For every ten-degree drop in temperature, the air inside a tire loses roughly 0.07 to 0.1 bar of pressure. If you inflated your tires in October at twenty degrees, by January at minus ten the pressure has dropped by 0.2 to 0.3 bar. Under-inflated tires deform more, increase the contact patch and add drag. Check pressure at least once a month during winter, always on cold tires.
Electrical Loads, Denser Air and Winter Fuel Blends
Rear window heater, heated seats, cabin fan at full blast, headlights on all day in the short winter daylight, wipers, and sometimes the air conditioning to help defrost the windshield. Each of these draws current from the alternator. The alternator consumes mechanical engine power, and the engine pays for that power with fuel. On gasoline engines the effect is slightly more pronounced because the alternator is relatively larger in proportion to engine output. When all consumers are switched on at the same time, alternator load can add 0.2 to 0.5 litres per hundred kilometres.
Cold air is denser, which means greater aerodynamic drag on the open road. At city speeds the effect is negligible, but at motorway speeds every percentage point of denser air counts. Snow and slush on the road surface create additional rolling resistance because the tire has to push mass ahead of itself. Driving through five centimetres of fresh snow can raise consumption by 20 to 30 percent compared to dry tarmac.
Winter gasoline and winter diesel have adjusted chemical compositions, higher volatility for gasoline and anti-freeze additives for diesel. This slightly reduces the energy content per litre. The effect is small, one to two percent, but it is real.
LPG Specifics, Why Gas Seems More Expensive in Winter
Drivers running LPG often notice that their range on gas shortens during winter, but the reason is not always the gas itself. Most LPG systems switch from petrol to gas only after the engine reaches a certain coolant temperature, usually 35 to 40 degrees. In winter that warm-up phase on petrol takes longer, sometimes five to seven minutes instead of the usual one or two.
On short trips the engine may spend half the drive on petrol, so it looks as though "gas consumption" is poor when in reality it is the petrol phase that consumed the fuel. If you track petrol and gas consumption separately, the winter petrol average will be noticeably higher.
In our experience, a normal winter increase in consumption is 10 to 20 percent compared to summer. City drivers on short commutes can see up to 25 percent. If your summer average is six litres per hundred kilometres, 6.5 to 7.5 litres in winter is within the expected range.
When should you suspect a fault? If the increase exceeds 30 percent, if the temperature gauge never climbs to the middle, if the cabin heater barely works, or if the engine runs rough for a long time after starting. The most common culprits are a thermostat stuck open, a faulty coolant temperature sensor, or worn glow plugs on a diesel engine. We cover the full diagnosis of abnormal consumption in our guide on increased fuel consumption.
For practical steps to reduce consumption year-round, including winter-specific tips, see our guide on how to reduce fuel consumption. If your consumption seems to exceed the winter norm, or if your car struggles to start in the cold, bring it in for an inspection. As part of a basic service we check the thermostat, oil, filters and everything that affects winter economy. Reach out via our contact page, there is no reason to wait until spring while the engine runs in a mode that costs you extra.