FAILING GLOW PLUGS

The vehicle will be very difficult to start when cold, with extended engine cranking, sometimes even to the point where battery power is exhausted and the engine still hasn’t started. The likely culprit is failing glow plugs. On older diesel engines that are indirect injection units, like the one in this 206, operation of the glow plugs is critical to cold starting, whereas in modern diesels their main role relates to emissions control.

Getting to the glow plugs involves removing the inlet manifold and the throttle intake valve. Once you have reached the glow plugs, it’s worth giving all the components a good clean using carburettor/throttle body cleaner, and it’s also wise to renew the O-rings that seal the manifold.

Now test the glow plugs, ensuring that they are receiving 12 volts with initial ‘key on’. The length of time during which 12 volts is supplied depends on the temperature of the engine, but the critical aspect is that each glow plug does receive the correct voltage. A simple resistance check on each glow plug will show up the offending cylinder; most of the time the plug will go open circuit so no resistance will be shown.

Next, when removing glow plugs, ensure the engine is warm and that the glow plug thread areas have a good covering of water dispellant/penetrating lubricant spray. The glow plugs are prone to seizing in the cylinderhead and snapping, so take care. Always opt for good-quality glow plugs, and we recommend that a light coating of copper-based anti-seize grease is applied to their threads on assembly. They should always be torqued when fitted to ensure that they are not over-tightened.