Car Won't Start in Cold Weather: Petrol and Diesel Checks

Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent

Listen first: what the car does when you turn the key

Turn the key once and listen. The noise narrows the problem down quickly.

• Slow, groaning crank that gets weaker: the battery is low or worn. This is the classic frosty morning failure.
• Rapid clicking, dash lights flicker: the battery has enough charge to light the dash but not enough to turn the starter.
• One loud click, lights stay bright: likely the starter motor, its solenoid or a poor connection.
• Normal speed crank but it won't fire: the battery is fine. Think fuel, spark (petrol) or glow plugs and fuel (diesel).
• Nothing at all, no lights: a completely flat battery, a loose terminal or, on some cars, a key fob or immobiliser issue.

For a deeper look at telling these apart, see our guide on battery, starter motor or alternator faults.

Petrol cars: checks you can do on the driveway

Petrol engines usually start well in the cold if the battery is healthy, so a slow crank is still the first suspect. If it cranks at normal speed but won't catch, try these safe checks.

1. Turn off everything that draws power: heater fan, heated screen, lights and radio. Every amp helps the starter.
2. Press the clutch fully on a manual while cranking. It means the starter is not also turning the gearbox oil, which is thick when cold.
3. Check there is fuel. A gauge near empty is worth taking seriously.
4. If it fired briefly then died and you have tried several times, stop. You may have flooded it. Wait 15 to 20 minutes before trying again.

If the engine catches but runs roughly or the engine management light comes on, a weak ignition coil or worn spark plug is common in damp weather. Our guide to worn spark plug symptoms explains the signs.

Diesel cars: glow plugs and fuel

Diesels rely on compression heat to ignite fuel, which a cold block makes harder. Glow plugs preheat the chambers to help.

• Turn the key to the position where the dash lights up and wait for the coil shaped glow plug light to go out before cranking. On a frosty morning, cycling the ignition once more can help.
• If the glow plug light flashes while driving, there is a fault in the system. Our article on the glow plug light flashing covers what that means.
• In very hard frosts, diesel can start to form wax that blocks the fuel filter. UK forecourts sell winter grade diesel from autumn, but an old or neglected fuel filter makes waxing more likely. See diesel won't start in the cold for more detail.

Why Kent winters catch batteries out

A lot of driving around Aylesham and the villages towards Canterbury and Dover is short trips: the school run, the shop, the station. A short journey with lights, wipers and heater running often puts back less charge than the start took out. Do that all week, add a few nights near freezing, and Monday morning is when the battery gives up.

Cars parked near the coast in Deal, Dover and Folkestone also suffer damp around terminals and earth straps. White or green crust on the battery posts is worth getting checked.

When to stop trying and get help

• You smell fuel strongly around the car.
• You see smoke from under the bonnet, or hear a grinding noise from the starter.
• You have tried three or four times and nothing has changed.

Jump starting can get you going, but a car that needs a jump every cold morning has a fault that will not fix itself. Do not use jump leads if the battery is cracked, swollen or leaking.

How we can help

If your car won't start at home or at work, we come to it. We test the battery and charging output, check the starter circuit and earths, read fault codes with a code reader, and on diesels test the glow plug system and look at the fuel filter. Labour is £30 to £50 per hour depending on the job, and you get a quote before any work starts. Send your reg and postcode on WhatsApp 07563 350335 or use our contact page. For wider winter preparation, our winter car checklist for Kent drivers is a good place to start.

Frequently asked questions

Why does my car start fine in summer but not on frosty mornings?

Cold reduces the power a battery can deliver and thickens engine oil, so the starter has less to work with just when it needs more. A borderline battery often fails on the first hard frost.

How many times should I try to start a car that won't fire?

Crank in bursts of about 10 seconds with a 30 second rest, and stop after three or four attempts. Constant cranking flattens the battery and can flood a petrol engine.

Is it the battery or the starter motor?

Slow cranking or dim dash lights usually point to the battery. A single loud click with bright lights is more likely the starter or its wiring.

Can you come out if my car won't start at home?

Yes, if it is at your home or workplace in our area. Send your reg and postcode on WhatsApp and we will tell you what we can do.