Car won't start in the cold? Possible causes and preventative tips

Car won't start in the cold? Possible causes and preventative tips
When the temperature drops, you may experience problems with starting your car.

Cold, damp weather can play havoc with batteries, fuel systems, starter motors, alternators, oil and – where fitted – carburetors.

Here we take a look at the possible causes of why your car isn't starting, first looking at the most common cause - the battery.

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Car battery problems

Car won't start in the cold

If your car won’t start in cold conditions, by far the most likely cause is the battery.

A vast number of RAC patrol winter callouts are battery-related. It may just be as simple as jump starting it or recharging it, let's look at the symptoms.

Symptoms

If you hear a faint whining noise when you turn the key in the ignition, but the starter motor doesn’t turn over, the likelihood is you have a flat battery.

If battery charge is totally depleted, or the cables to the battery have come loose, you may not hear anything.

Further signs of a completely flat battery include the ignition lights on the dashboard failing to illuminate, and the car refusing to unlock via remote central locking.

MORE ADVICE: Is it illegal to drive with snow on your car?

Solutions

If you are in a hurry and need to get moving fast, you can attempt to jump start your car. You will, however, need access to jump cables and another vehicle.

If you think your battery needs replacing, you can call 0333 2000 999 for The RAC Battery Fitting Service.

Alternatively, you can visit our car battery section to find out which product you need. We can deliver the battery to you, and fitting is free for RAC members.

How can I help maintain my battery during the winter?

With more and more vehicle equipment demanding electricity battery maintenance is more important than ever.

Cold temperatures affect the chemical process inside the battery that produces and stores electricity, effectively slowing it down and reducing its ability to hold a charge.

If you are using your car regularly for short trips, it may be worth charging your battery at least once a week during the winter months, particularly if the battery is more than three years old.

We would also recommend a car battery comfort indicator to help monitor the battery’s condition.

You can find more about how to charge car batteries on our car battery chargers page.

Older, weaker batteries will typically already have reduced performance and cold temperatures will often drastically reduce this further, to the point where the battery will discharge or go flat very quickly.

If you are finding that the battery isn’t holding a charge very well at all then it might be time to replace it, in which case we would again recommend either visiting our car battery section or calling The RAC Battery Fitting Service on 0333 2000 999

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What else can I do to help my battery during winter?

A bit of basic preparation and maintenance can work wonders for battery life.

Remember to:

  • Switch off all loads, including the lights, wipers, heater and radio before turning off your engine at the end of a journey. This prevents any unnecessary drain on the battery the next time you start up
  • Look for corrosion on the battery clamps and cables. This could restrict the flow of current. When the engine is off, clean it off using a wire brush, or ask a mechanic to do so
  • Check that everything is switched off before turning the ignition on
  • Avoid using heaters, heated screens and heated seats for longer than you have to. They all put high demands on the vehicle’s battery. Some satnavs, in-car DVD players and MP3 players can also drain the battery if left connected
  • Check that there are no interior lights, including boot lights, left on – or any accessories such as phone chargers left plugged in
  • Park your vehicle in a garage if you are able to, especially in very cold temperatures
  • Get your battery properly tested, particularly if it is over three years old

And, sometimes it can be difficult just getting into your car. These two tips could save you some much-needed time:

  • Use a little silicone-based furniture polish on the rubber door seals – it helps prevent doors getting stuck when it freezes. It’s best to apply with a cloth so you don’t spray polish on to the vehicle’s paintwork
  • If locks are frozen, try warming your key. You could also inject the lock with the appropriate anti-freeze or spray it with WD40

WINTER ADVICE: Don’t get fined for de-icing your car

Alternator problems

Car won't start - alternator

The alternator is an electrical generator that charges your car’s battery when the engine is running. If you have a relatively new battery and it keeps going flat, the problem probably lies here.

Symptoms

If you jump start your car and the engine dies immediately, this points to a faulty alternator.

You may also notice your headlights and dashboard lights flickering, the car’s gauges moving in a jerky manner – and even a burning smell filtering into the cabin if the alternator has recently overheated.

Solutions

The alternator is connected to the battery and the engine, so, unless you’re an able mechanic, replacing one is a job best left to the experts.

It shouldn’t be difficult to source a new part, or you can opt to have your existing alternator reconditioned. The job shouldn’t take a garage more than two hours.

READ MORE: 10 checks to prevent a breakdown this winter

Starter motor

Car won't start in the cold - starter motor

The starter motor does exactly what you’d expect; it uses electricity from the battery to jolt the car’s engine into life.

Many modern cars now have stop-start systems with stronger starter motors to cope with the demands of frequent engine on/off cycles in traffic.

Symptoms

The most obvious sign of a broken starter motor is a clicking sound when you turn the ignition key, followed by the engine refusing to turn over and start.

If all the lights and in-car electrics are working fine, this also points to an issue with the starter motor – rather than the battery.

Even jump starting won’t work if the starter motor has failed.

Solutions

Again, replacing a starter motor is generally a task for a trained mechanic.

They’re not hugely expensive, but the work may take up to half a day.

Your old starter is usually exchanged for a new one, which may look different; manufacturers sometimes modify the designs.

Car fuel system problems

Car won't start - fuel system

Over time, car fuel systems may become contaminated with water.

This can cause combustion problems and, if cold weather makes the water freeze, prevent the engine running altogether.

The issue is most acute in the fuel lines, which feed the individual injectors.

These are very narrow and can be blocked by tiny ice particles, starving the engine of fuel.

Symptoms

Aside from the engine not starting, other symptoms of fuel system problems include a stuttering engine – particularly when accelerating – and a generally jerky feel to the car’s power delivery.

The engine may even cut out altogether while driving.

Solution

If you car has water in its fuel lines, you may need to have the system professionally flushed.

However, certain additives can reduce contamination by using alcohol to hold water in suspension, then passing it out through the exhaust.

You can cut the risk of water ingress by keeping your car’s fuel tank close to full, thereby reducing the likelihood of condensation.

Note that diesel fuel can ‘thicken’ and become less free-flowing in cold conditions, too – another obstacle for your car to overcome in winter.

READ MORE: Winter breakdown kit checklist

Are you using the wrong oil?

Car won't start - oil

Oil also becomes less free-flowing in cold conditions.

And that, in turn, puts additional strain on your car’s battery by making it harder for the engine to turn over and start.

Symptoms

If your oil has too much cold viscosity (resistance to flow), you won’t be able to start your car in cold temperatures. On the flip side, excessive hot viscosity means engine components won’t be adequately protected, leading to premature wear.

Solutions

Check your car’s handbook to see what type of oil the manufacturer recommends, and switch to a thinner grade if possible in winter.

Typical grades include 10W-30 and 5W-20, with the first number (followed by a ‘W’ for ‘winter’) denoting the oil’s thickness in cold weather. The lower the number, the thinner the oil.

For cars operating in very cold climes, even 0W oil is available.

Cars with carburetors

Car won't start - carburetor

If your was built more than 30 years ago, it’s likely to use a carburetor.

These regulate the mix of fuel and air for combustion, but are particularly vulnerable to icing up.

If the nozzles of the carburetor become clogged with ice, the engine may not start – and certainly won’t run properly.

With your left foot on the clutch, try gently pushing the accelerator pedal when you start the engine in cold weather.

This will pre-inject a small quantity of fuel to give the engine a helping hand.

All modern cars use fuel injection, and thus aren’t affected by this problem.

Getting into your car

Sometimes it can be difficult just getting into your car. These two tips could save you much-needed time:

  • Use a little silicone-based furniture polish on the rubber door seals. It helps prevent doors getting stuck when it freezes. It’s best to apply the polish with a cloth, so you don’t spray it onto the vehicle’s paintwork
  • If the locks are frozen, try warming your key. You could also inject the lock with the appropriate anti-freeze, or spray it with WD40

6 Fitting is Free for RAC members, for non members garage fitting is £9.99 and patrol fitting £30.

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