There does not seem to be a way of editing my previous article so it is necessary to write an add-on. As to the cooling system on the Discovery 300Tdi I cannot say enough bad things about it, in fact it seems almost as if the designers had a grudge against the factory and were incorporating design faults deliberately in order to get some kind of revenge. One appalling gaffe is the cylinder head temperature sensor moulded from thermoplastic (thermoplastic is plastic that can be re-melted by heating) Now in my honest opinion the temperature sensor should be moulded from thermosetting plastic (plastic that cannot be re- melted by heating, phenolic resins such as Bakelite are in this category). The scenario is that one is ascending a long hill towing a trailer in the dark. The temperature gauge rises to maximum then begins to fall once the summit is reached. A reasonable person might deduce that the engine is now cooling after the hard work of climbing the hill. WRONG! What has actually happened is that the plastic temperature sensor has melted and the actual sensing element has moved away from the cylinder head. The high mounted water pump, the oil cooler combined with the radiator and the viscous coupled fan also conspire to produce large repair bills. OK it works OK when it is new but doesn't everything? If buying a Disco examine the radiator very carefully and if there is any doubt about the rad BIN IT! (Also research "Tropical Mod" - some radiators were made where the coolant could bypass the radiator tubes and go directly from input to output ! The tropical modification involves blocking up the bypass so that the radiator works properly).
Incidentally a similar design fault is present on the Range Rover classic. On these the temperature sensor is on the inlet pipe to the radiator. Once the water and steam have all gone, the temperature gauge will indicate that the engine is now cooling down, duh!
The Discovery is by no means the only car that has an iffy cooling system as numerous foreign cars have cooling systems that incorporate bleed screws for letting the air out. Some even need to be vacuum-bled! Avoid such vehicles like the plague as a proper design will be self-bleeding.