Preheaters

Ross · Post by **Ross** » 07 Mar 2005, 12:32

Do the preheaters on a 106 diesel stay on for a longer period than indicated by the dashboard preheat light indicates ? I have been told the relay for the preheaters is defective as the preheaters should be staying on longer whilst the engine warms up and the cylinders get hot enough to assist in detonation of the diesel - at the moment the preheaters go off when the light goes out on the dashboard and i get a lot of smoke on start up and for the first 8-10 minutes
thanks

JohnD · Post by **JohnD** » 07 Mar 2005, 14:51

Yes they do. If you don´t start the engine when the light goes, after several seconds, you´ll hear the switch click off.

rotodiesel · Post by **rotodiesel** » 07 Mar 2005, 23:54

The glowplugs on the TUD5 engine in the 1.5l 106 are fast plugs from Beru. The pre-heat time is determined by a thermistor in the controller, which is bolted to the coolant header tank. The post heat (after engine starts) is determined by engine coolant temperature, measured by a thermistor in the cylinder head, near the thermostat.
The maximum pre-heat for these plugs is 5s, reducing to zero with a very hot engine. Post heat varies from a few seconds with a hot engine, to over 5 minutes with a very cold engine.
A common misconception on this website is that glowplugs switch off when the dashboard light goes out - they don't. The Lucas glowplug controller does contain two safety devices. The first is a "time out" after about 20s, which switches off the plugs if the engine is not started, or doesn't start and the key switch is left on. This reduces needless battery drain. The other is a short circuit overcurrent sense, which causes the relay to drop out if the controller has to provide too much current. This is why there is a voltage driop across the controller, for the current measuring shunt. I would not recommend testing this second safety device, although it has prevented a few fires. Only fit Beru plugs.
rotodiesel.

rotodiesel · Post by **rotodiesel** » 08 Mar 2005, 01:37

Ross, I've just re-read your original message. If you have no post-heat, a possible cause is either a faulty thermistor in the cylinder head (I think it's the green one) or the connections to it. It's worth a look before buying a controller.
rotodiesel.