water pre-heater

[HDi--Power]

They simply cycle on for 30 seconds then off for a few then back on for 30 seconds constantly regardless of all other conditions. They remain on even when the car is up to operating temperature. They are controlled by the two relays in the black box behind the ecu (two plugs per relay) and are separate to the engine glow plugs. They do help with clearing the windscreen but I have never seen a car heat up in less than 15 mins with them working away full blast so their effect is not as amazing as people think.

also they are NOT 1.9 glow plugs iirc