Diesel Won't Start in Cold Weather
Why diesel engines struggle more than petrol in winter, and how to prevent it.
Diesel engines are more sensitive to cold weather than petrol engines, relying on glow plugs to warm the combustion chamber and on fuel that stays liquid at low temperatures. When either of those fails, a cold morning can turn into a no-start situation.
Signs of a cold-weather diesel fault
- The engine cranks for longer than usual before starting
- The glow plug warning light stays on longer than normal
- The engine starts but runs roughly for the first minute
- The car won't start at all on very cold mornings
- White smoke on start-up in freezing temperatures
Common causes
- Worn or failing glow plugs not heating the combustion chamber enough
- Diesel fuel waxing — forming wax crystals that block the fuel filter in extreme cold
- A weak battery struggling to provide the extra cranking power diesel engines need
- A failing glow plug relay or control module
- Water in the fuel system freezing in cold conditions
How it's diagnosed
We test glow plug function and resistance, check the fuel filter for signs of waxing, and confirm the battery has enough cranking power for a diesel engine's higher demands. Most cold-start faults are traced to one of these three areas.
What to do next
Avoid repeatedly cranking a diesel that won't start in the cold — this can flatten the battery quickly given how much current diesel starters draw. If it happens more than once, it's worth having the glow plugs and battery checked before the next cold snap.
Frequently asked questions
They heat the combustion chamber before starting, helping the diesel fuel ignite reliably in cold temperatures.
Diesel struggling to start in the cold?