Glow Plug buying guide — what to know before you buy
Glow plugs heat the combustion chamber in diesel engines to aid cold starting. Failed glow plugs cause hard starting in cold weather, rough idle until the engine warms up, and white exhaust smoke. Seized plugs are a common complication during removal. At CarParts247 we stock glow plugs from Bosch, NGK, and Beru for all popular diesel engines.
Glow plug failure symptoms
Glow plug failure is most noticeable in cold weather. One failed plug may cause slight roughness; multiple failures can prevent the engine from starting entirely.
- Hard or extended cranking in cold weather — glow plugs not heating properly
- Glow plug warning light stays on or flashes — ECU detected a fault
- White smoke from the exhaust on cold start — incomplete combustion
- Rough idle for the first few minutes until the engine reaches temperature
- Misfire codes on specific cylinders during cold start
Removal tips for seized plugs
Glow plugs seize in the cylinder head due to carbon build-up and corrosion. Forcing a seized plug risks snapping it in the head — a costly repair.
- Warm the engine before attempting removal — thermal expansion helps free seized plugs
- Apply penetrating oil to the plug threads several days before attempting removal
- Use the correct deep socket — glow plugs are fragile and snap easily
- If the plug won't turn, stop immediately — specialist removal tools or reaming may be needed
- Consider replacing all glow plugs at once — they are the same age and condition