Many drivers assume that diesel glow plugs are only necessary during deep, -20°C winter freezes. Because of this, when the thermometer hits zero in late October and the starter cranks for 10 seconds, the engine stutters, coughs blue smoke, and refuses to fire up, it comes as a major shock. Usually, the culprit is one or two faulty glow plugs.
Why are modern Common Rail diesel engines so sensitive to the health of their glow plugs?
The Role of Glow Plugs in Modern Engines
In older diesels, the glow plug served only one purpose: to heat up to a glowing red before startup and then shut off. In modern diesel engines, however, glow plugs perform two vital additional functions:
- Post-Heating: After the engine starts, glow plugs continue to operate for 2 to 4 minutes at a reduced voltage. This ensures smooth fuel combustion in a cold cylinder, reduces vibrations, and prevents excessive smoke.
- DPF Regeneration Support: When driving on the motorway, the engine control unit engages the glow plugs to raise exhaust temperatures to 650°C to burn off soot. If even one plug is faulty, DPF regeneration can be blocked entirely!
Check your glow plugs well before the first true frost arrives. If you find yourself stranded with a dead battery and a diesel that won't start, take a look at our breakdown and towing service price list and call for technical assistance.