Diesel glow plugs

Posted on December 28th, 2021 by GEM Motoring Assist

Modern diesel engines tend not to require pre-warming in normal weather, unlike their ancestors. Yet, an electrical heater/glow plug is still fitted. Therefore, you might not notice that a glow plug has deteriorated, or stopped working, until your car appears hesitant to start on a cold morning. It may even misfire, or run unevenly until it has warmed.

On the latest diesel engines, glow plugs have another role to play. Should one of them stop working, it can prevent the diesel particulate filter (DPF) from self-cleaning. Therefore, a problem with a blocked DPF is not down to the filter but the glow plugs. Unless the underlying glow plug problem is addressed, paying a garage to clean the DPF can be pointless.

Whether paying a garage to do the work, or you conduct the work at home, consider that replacing glow plugs is not always straightforward. They are delicate components and can snap, as they are extracted from the cylinder-head. Removing a broken glow plug may necessitate involved engine dismantling and put the car out of action for some time.


Furthermore, glow plugs should be replaced in engine sets. Changing just one is not best practice. In some cases, the control relay should also be renewed as well, adding to the expense. So, if a garage recommends these extra parts, you are not being hoodwinked and the recommendation is correct.