There’s nothing quite as frustrating as a car failing to start on a cold winter’s morning when you need it, and you can bet your life savings on it being exactly when you have somewhere important to go to.  

Thankfully, there are a few common causes for a car not starting in the cold and luckily there are a few things you can do to head them off. We’ll explain the most common causes of non-starting engines on cold days, and how to prevent them. 

Why does my car not start in the cold? 

The most common reason for a car not starting in the cold is an old or worn-out battery. As the temperature drops so does battery performance, a particularly cold morning is often just enough to prevent the car from starting.  

Can an old battery cause starting problems in the cold? 

The most common cause of an engine not starting in winter is a bad battery. If your battery is a few years old or damaged through non-use, the drop in temperature can be just enough to prevent the engine from turning over. 

Car won't start but the lights come on 

It’s entirely possible that your battery is dead enough to not be able to start the engine, but still have enough power to turn on your lights or radio. 

An engine takes quite a lot of torque to turn it over fast enough to start the combustion cycle, this torque comes from the starter motor, using power from the battery. Dashboard, interior, and even headlights all need a comparatively small amount of energy.  

Does fuel freeze? 

Yes, but we are unlikely to see this happen in the UK. Diesel will turn to gel at -12°C, and petrol will take -60°C to freeze.  

However, whilst diesel needs over ten degrees below freezing to gel, any water that has made its way into the tank will freeze readily as normal. This can cause problems if it freezes in fuel lines.  

Ice in fuel lines 

Water can make its way into the fuel system of your car, usually via condensation inside the fuel tank. If this happens, and the water freezes, no fuel will be getting to the engine until the blockage defrosts. 

Diesel car turns over but won't start 

If your diesel engine is spinning as fast as normal, but refusing to fire, there could be an issue with your glow plugs.  

Diesel engines use glow plugs to warm the cylinders before the fuel is injected, this helps initiate combustion. 

Old and worn-out glow plugs will have reduced effectiveness, meaning the engine takes a lot longer to start. Check for a glow plug light on your dash when turning over.

6 Tips To Make Sure Your Car Starts In Cold Weather  

1. Keep on top of battery replacement 

As bad batteries are the most common cause for starting issues in the winter, listen out for how fast your engine turns over when trying to start, especially as the weather begins to change at the end of Autumn. 

Battery monitors can be bought relatively cheaply and will tell you how healthy the cells are at any time. Once a battery is below 40% health, especially if it's 8 years or more old, it would probably be worth getting a replacement. 

For information on what battery you should buy, we have a guide. 

2. Turn off ancillaries 

Lights, heater fans, and radios all draw current, turning these off whilst trying to start the car will allow as much power to be delivered to the starter as possible.  

Remember that some cars turn the heated windscreen or rear window on automatically in cold weather - so check this and turn them off if necessary.  

3. Buy a jump starter 

If you are very concerned about battery issues, a jump start will allow you to drive to a garage to have your battery replaced, as soon as it becomes an issue. Jump starters can be bought for around £50, and will start a car with a dead battery 1 to 2 times per charge. 

These are safer and a lot more convenient than jump-starting from another car. 

4. Keep your car in a garage 

Whilst not possible for many, keeping your car inside a garage, even one not connected to a heated home, will help it stave off the worst of the cold weather. 

5. Keep your tank full and check the fuel cap 

Any water that makes its way into your fuel system will do so through condensation inside the fuel tank. When you open the fuel cap, humid air will fill the space not occupied by fuel. Keeping your tank at least half full will reduce the amount of vapour that can enter your tank.  

Similarly, a badly sealed fuel cap will allow humid air in, inspect the seal to be intact and free from rips, tears, or holes.  

6. Use a diesel fuel additive 

If very cold weather is predicted, say below -12°C, and you have a diesel car, it would likely be beneficial to add a ‘diesel antifreeze’ to your fuel. This additive allows the fuel to experience -40°C before gelling.  

Allow your glow plugs to warm up 

If your diesel car has a traditional key to start and not a push-button, you can give it a fighting chance by allowing the glow plugs to fully warm up before starting.  

To do this: 

• Turn the ignition on - usually by turning the key to the second click, lights will appear on the dash 
• Locate the glow plug light - a coil symbol that looks a bit like a spring  
• Wait for this light to go off - this means the plugs have completed their pre-warming cycle 
• Repeat one or two more times if the car often struggles to start 
• Start the car 

If this problem persists, and this trick helps, you should look to have your glow plugs replaced as soon as possible.  

Look forward to summer 

So, that’s all you need to know about winter starting issues, thankfully here in the UK we don't have extremely cold winters, with the average temperature being around 2°C. Comparing that to somewhere like Canada, at -15°C average, we should consider ourselves lucky! 

Ask an expert 

If you’re unsure what the problem is find a trusted repairer on the Bumper network. 

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