It’s one of those questions that car owners often wonder about, especially on cold winter mornings. Although the idea of starting your car and leaving it ‘ticking over’ for a while is a popular one, is it really the best thing for you… or your car? We take a quick dive into the subject and discuss a few of the pros and cons here.
Warming your car up first in cold weather – The pros
It makes it nice and warm – This, of course, is a self-evident truth. If it’s a cold and icy morning outside and your car’s engine is left running to warm it up, the ice on the windows will be easier to scrape off and you can leave the fan on to warm the interior up too. You may also benefit from clearer windows if any condensation on the windows inside has evaporated first.
You’ll be able to drive away at your usual pace – If you start your car and drive off straight away, it’s recommended that you drive it more gently until the engine reaches its normal operating temperature. If it’s already warm, you won’t need to do this.
Leaving your car idling in cold weather – The cons
It might be illegal – Aside from the unnecessary pollution to the environment, if you leave your car’s engine idling to warm up whilst it’s on a public road, you’re committing an offence under “The Road Traffic (Vehicle Emissions) (Fixed Penalty) (England) Regulations 2002” in England (here). A similar idling law applies in Scotland. According to Wales Online, it’s also specified in The Road Traffic Act and mentioned in Rule 123 (The driver and the environment) of the Highway Code as “You MUST NOT leave a parked vehicle unattended with the engine running or leave a vehicle engine running unnecessarily while that vehicle is stationary on a public road”. It would therefore apply in Northern Ireland as well.
However, if your car is on private land e.g. your driveway or a private car park, the regulation doesn’t apply and it’s therefore not illegal. Bear in mind it’s still not nice for those who have to walk past whilst breathing in your car’s toxic fumes though.
Car theft – Perhaps most obviously, it leaves you open to being a victim of car crime. There’s a good chance that, especially if it’s a cold winter’s morning, you’ll nip back indoors to keep warm.
With your car idling, the keys in the ignition and the doors open, any passer-by can simply jump in it and drive straight off. To make matters worse, it will almost certainly invalidate your insurance policy, meaning your insurance company will refuse to pay out.
Wear and tear – Many years ago when cars had old-style carburettors and a manual choke, it was deemed essential to leave your car running for a while in cold weather to warm it up to prolong the life expectancy of the engine. If you “thrashed it” when it was cold, it did indeed have a detrimental effect on the engine. The car would also be more difficult to drive as it would, jump, cough and splutter for a while until it reached its optimum running temperature.
However, that’s not the case anymore. According to Douglas Longman who works at the U.S. Department of Energy as an engine specialist, a modern-day car has an electronic fuel system, the car owner only needs to let the car idle for about 30 seconds before driving off.
The takeaway from this means that if you leave your car running for longer than necessary, it doesn’t benefit the engine and will, in fact, decrease rather than prolong the lifespan of the car overall.
Furthermore, if you are assuming that it’ll help your battery to charge up, this isn’t necessarily true. For example, if you have heated windows, your headlights and the hot air blower all switch on while the car is only at idle speed, it can actually drain your battery further, rather than charge it up.
Fuel consumption/cost – You may not think it makes much difference if your car is idling for 15 minutes to warm up but the cost of doing so can add up over time.
This is obviously dependant on how long on average you leave it running for prior to pulling away but, according to a study carried out a few years ago, the U.S. motorists who used this strategy left their car warming up for an average of 16.1 minutes per day. If you do this every morning in the winter, it’s very uneconomical and it’ll certainly make a big dent in your monthly petrol or diesel bill.
Air pollution/ CO2 emissions – If you take a look at the study linked to in point 3, you’ll see in the Conclusion on page 6 the practice of those who leave their cars to warm up accounts for around 94 million tonnes of annual CO2 emissions in the US alone, which equates to over 10 BILLION gallons of fuel!
We hope this post has given you some useful information to help you decide if letting your car warm up for a while is the best thing to do or not – We’ll leave it up to you to make up your own mind…
Letting your car idle to warm up on cold mornings is convenient but not always the best approach. Modern engines are designed to warm up faster when driving, reducing fuel waste and emissions. For better results, scrape ice manually and drive gently until the engine warms up. Explore winter car care tips for efficient and eco-friendly ways to handle cold mornings.
Hello what would you say is the ideal temperature of the car before you start driving it as yesterday I drove of strait away as soon as I deiced the car and engine management come up twice then after that didn’t see it again today I was a bit unsure so left the car running for a bit so far I have got to location 1 and no engine light hopefully fingers crossed I don’t see engine malfunction
Hi Gareth. The ideal temperature for your car’s engine before you start driving it can vary depending on several factors, including the make and model of your vehicle, the outside temperature, and the type of engine it has (e.g. petrol, diesel etc.).
If it’s very cold, you could let your car idle for a minute or two after starting it. This allows the engine oil to circulate and lubricate all the engine components properly. This should help reduce wear and tear. As a general rule of thumb, modern engines are designed to warm up relatively quickly, so you don’t need to let your car idle for an extended period of time.
As for the engine management warning light you mentioned, this can be triggered for various reasons, including sensor issues, low battery voltage, or other issues with the engine or vehicle systems. For example, if you’ve left it idling and have the headlights on, heater/blower on and also the screen demister on(if you have one), then this can certainly drain the battery quite quickly
If the light came on and then went off, it’s a good idea to have your car’s onboard diagnostic system scanned for error codes. This will help identify the specific issue that triggered the warning light, and you can take appropriate action to address it.
I think it is now illegal in the UK to let your car run idle due to pollution to people passing by.
Hi Jen and thank you for making this very pertinent comment. You are indeed correct, leaving a car idling on a public road is illegal and we’ve now updated the post to reflect this fact.
this depends on where you live. My car is on my driveway so it is less likely to disappear than if I lived in a towerblock and had to leave it running while going down/up two flights of stairs to my flat. I leave my car warming up on my drive in summer and winter without an issue.
Why would you bother to warm it up in the summer😂
I always used to leave my car running to warm it up on cold winter mornings. That was until about 3 years ago when someone stole it from outside my house!