Car preheating - when and how?
Author:
Miia Väänänen
Copywriter
Published:
03.11.2025
Updated:
16.10.2026
A cold morning, frosted-over windows and an engine that struggles to turn over – a familiar scene in a Finnish winter. Preheating your car solves these problems: timed correctly, it saves fuel, protects the engine and makes leaving home in the morning much more pleasant. As a rule of thumb, it's worth starting to preheat the car once the temperature drops below +5°C. The colder it gets, the longer the preheating time should be. This guide covers when to start preheating, how long to warm up the car at different temperatures, how to schedule the heating smartly, and how preheating works in an electric car.
What is car preheating and why does it matter in winter?
Preheating a car means warming the engine and cabin with electricity before you set off. An engine heater keeps the engine oil and coolant warm, while a cabin heater takes care of comfort and defrosting the windows. There are three main types of engine heater: a block heater (fitted directly into the engine block), an in-line coolant heater (fitted into a coolant hose), and a dipstick-type radiant heater (fitted in place of the oil dipstick, for example). In everyday speech, "block heater" is often used loosely to mean any of the three, even when it's technically an in-line or dipstick heater. In winter these matter because a cold engine burns more fuel, wears out faster and produces more harmful emissions.
Preheating protects the car's mechanical parts, because cold oil doesn't lubricate as effectively as warm oil. A preheated engine starts more easily and reaches its optimal operating temperature faster. Cabin heating, in turn, improves visibility and safety by clearing frost and condensation from the windows.
In Finnish winter conditions, preheating is practically an essential comfort feature, but it's also a smart way to extend your car's lifespan. Knowing when and how long to heat the car gets you the full benefit without wasting energy.
When should you start preheating your car?
It's worth starting to preheat your car once the temperature drops below +5°C. That's the point where a cold engine start begins to burn noticeably more fuel and put extra strain on the engine. The colder it gets, the more preheating matters, both for comfort and for the car's condition.
In practice, keep an eye on the weather forecast and start preheating from late October onwards, once night frosts become common. Once temperatures rise back above freezing in early spring, preheating is no longer needed. If it's hovering around zero, you might only preheat in the mornings, when the frost is at its worst.
Don't preheat the car unnecessarily. It wastes electricity, and preheating brings no real benefit once the temperature is above +5°C. Preheating at the right time saves both energy and money, and keeps the engine in better shape for longer.
Does a newer car still need preheating?
The need for preheating isn't quite the same in every car. Newer combustion-engine cars often run on thinner oils, such as 0W-30, which stay fluid even in hard frost – so an engine heater brings less benefit than in an older car. If you're not sure about your own car, check the owner's manual or ask an authorised workshop. The older the car, the more clearly preheating shows up as both lower fuel consumption and less engine wear – which is exactly why it's worth factoring in when choosing a used car.
How long should you preheat a car before driving off?
The right preheating time depends on the outside temperature.
- Below +5°C, and around freezing in either direction, about 30 minutes is enough for the engine to warm up sufficiently and the cabin to start defrosting.
- In around -10°C frost, it's worth preheating for about an hour.
- Below -10°C, preheat for 1–2 hours, after which the engine is properly warm and the cabin comfortable.
The engine heater and cabin heater don't necessarily need the same amount of time. The engine heater usually needs longer, since its job is to warm the engine oil and coolant. The cabin heater can run for a shorter time if you only need to defrost the windows and warm up the cabin.
The right preheating time saves money and is better for the environment. A timer lets you automate the heating to start at just the right moment, for example before you leave for work. Overheating, on the other hand, just wastes energy: unnecessary or overly long preheating burns electricity for no benefit. Preheating for more than 3 hours isn't recommended.
Schedule your preheating smartly – timers and smart plugs
There's no need to leave an engine heater or cabin heater running all night – that's both unnecessary electricity use and unnecessary wear on the device. The smartest approach is to time the heating to start at just the right moment before you leave:
- A mechanical timer plug is the cheapest and simplest option, but it doesn't know the weather – you have to adjust the time yourself depending on the frost.
- A smart plug or GSM-controlled switch lets you start the heating from your phone whenever your schedule changes or you're in a hurry, without having to go out and plug the car in yourself.
- In many newer cars, scheduling the heating is built directly into the car's own system or the manufacturer's mobile app.
Scheduling also helps more broadly: when the engine and cabin heater aren't running all night but only right before you leave, you avoid adding unnecessary load to the power grid on the coldest mornings, when many other people are preheating their cars at the same time too. This is especially worthwhile if your electricity contract has a price that varies by time of day.
Webasto – flexible, fuel-based heating
Webasto is the common name for fuel-powered auxiliary heaters that use the car's own fuel (petrol or diesel) to warm the cabin and often the engine too. A Webasto heater is practical, since it lets you preheat the car anywhere, without needing an electrical connection – real convenience for everyday life!
- How it works: in older cars, a Webasto heater has typically warmed both the cabin and the engine. In newer cars – especially hybrids – a fuel-powered auxiliary heater is now mostly just a comfort heater that only warms the cabin: a modern engine no longer needs auxiliary heating the way older engines did, and emissions regulations don't always allow a fuel-burning device to heat the engine at all.
- Controls: remote control, timer, or a mobile app.
- Worth knowing: a Webasto heater uses fuel and also draws on the car's battery. Try to drive for roughly as long as you ran the Webasto heater, so the battery has time to recharge. It's also a good idea to run a Webasto heater regularly throughout the year so it stays in working condition.
What's the difference between engine and cabin preheating?
The engine heater and the cabin heater serve different purposes. The engine heater warms the engine oil and coolant, which protects the engine from wear and reduces fuel consumption when starting. The cabin heater, meanwhile, warms the interior and defrosts the windows, which improves comfort and visibility.
There's a difference in power draw too. An engine heater typically draws 400–800 watts, while a cabin heater can draw as much as 1,000–2,000 watts depending on the model. Together they can use around 2–3 kilowatt-hours (kWh) over a two-hour preheating session – still less than the extra fuel a cold start would burn.
You get the best result by using both together. Engine heating keeps the car mechanically sound, while cabin heating keeps you comfortable. Use both sensibly and you get a safe, comfortable drive off, whatever the weather.
How does car preheating affect fuel consumption and the environment?
Well-timed preheating cuts fuel consumption noticeably. A cold engine can burn up to twice as much fuel during start-up, because the oil is thicker and the engine isn't running efficiently yet. When you preheat the engine, it starts at its optimal temperature and consumption stays normal right from the start.
The environmental effects are just as clear. A cold engine releases more harmful emissions into the air, because the fuel doesn't burn completely. A preheated engine produces fewer emissions and runs more cleanly. The engine also wears less, which extends the car's lifespan and reduces the need for maintenance and repairs.
The cost of electricity is usually lower than the extra fuel it saves. Even though preheating costs a few cents each time, you save more on fuel and upkeep over the long run. Preheating is therefore sensible both financially and environmentally.
For the same reason, it's worth avoiding unnecessary idling once the car is already warm – idling for more than a short while burns noticeably more fuel than you might think, and under Finnish traffic rules idling is in any case limited to two minutes (four minutes in frost below -15°C).
What about preheating and range for electric cars in winter?
Preheating is worthwhile for electric cars too – in fact, it matters even more for an EV than for a combustion-engine car. Heating the cabin takes more energy in an electric car than in a conventional one, because there's no waste heat from a combustion engine to draw on. On top of that, a cold battery is less efficient – in a Finnish winter, an EV's real-world range can drop by as much as 40% compared with summer, which is worth bearing in mind especially when planning longer trips.
For this reason, it's best to preheat an electric car while it's still plugged in and charging: that way the preheating doesn't draw on the battery you need for driving, and the battery itself also has time to warm up to a better operating temperature before you set off. In most electric cars you can start preheating from the key fob, a phone app, or the car's own screen, and many models also have a timer.
Also worth remembering
Safety: preheating gives you better visibility, since the windows aren't frosted or iced over, which makes setting off safer. Besides visibility, tyres also play a big role in winter driving safety – read about how studded tyres affect handling stability.
Idling: under Finnish rules, you can let the engine idle for up to two minutes before driving off, but a short idling period of up to four minutes is allowed in frost below -15°C.
Frequently asked questions
Can you preheat a car too much? Yes – preheating for more than 3 hours is unnecessary energy use and doesn't meaningfully improve the result any further. A timer is the best way to make sure the heating stops right when you're about to leave.
Is it worth preheating a newer car too? The benefit is smaller than in an older car, since modern engine oils stay more fluid in the cold. Cabin heating, to defrost the windows and for comfort, is still worthwhile even in a newer car.
Can you schedule the engine heater and cabin heater together? Yes, and that's often the smartest approach: the engine heater has time to warm the oil and coolant, while the cabin heater defrosts the windows and warms the cabin right before you leave.
Does preheating an electric car use up the battery you need for driving? No, as long as you preheat while the car is plugged in and charging – in that case the electricity used for heating comes straight from the grid, not from the drive battery.
Does a newer car's auxiliary heater also warm the engine? In most newer cars, especially hybrids, a fuel-powered auxiliary heater is now essentially always a comfort heater that only warms the cabin. That's because a modern engine no longer needs auxiliary heating the way older engines did, and emissions rules don't always allow a fuel-burning heater to warm the engine at all. An electric auxiliary heater, meanwhile, does need some charge left in the high-voltage battery, but it heats faster and more efficiently, reaching the same end result.
If you're buying a car with winter in mind, it's also worth checking the condition of its heating equipment before you buy – read more about why buying a car in winter pays off.
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