Disco 2 poor starting

hi, I have a 01 plate td5 auto with 150000 on the clock. about 4 weeks ago it wastaking a good 10 seconds or so turning the starter to fire it up. this was in the mornings when cold, started up ok when engine was warm.later in the day. or though there were acouple of occasions in the afternoon when it was a bit slow to start had not used it for 3 or 4 hours. my mate said first port of call we will change the glow plugs which he did 2 weeks ago since then its started ok. this morning took 3 short turns on the starter to fire up normally starts as soon as the starter turns. not that cold this morning abuot 8 degrees or so .I have just noticed that as you turn the ignition on the glow plug warning light only lights up for about a half a second then goes out. ive had her for about 8 years now and never took any notice of how long the glow plug light had stayed on for is half a second ok or is not staying on long enough to heat up the glow plugs, any ideas welcome, many thanks, alan.

Alan make sure the glow relay is working ok leave the ignition on until you hear the fuel pump stops then swing her over to rule out any air in the system

alan morgan said:

I have just noticed that as you turn the ignition on the glow plug warning light only lights up for about a half a second then goes out.

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the warning light is managed by the engine ECU based o coolant temp(ECT) sensor input and it works regardless of the relay or plugs, if you have and can handle a multimeter ask somebody to turn ignition on and measure across body and C0622(attached) there should be voltage while the glow plug warning lamp is on(pre-heat operation) and after the engine started for a while depending on the ECT input untill it gets to 20*C(glow plug post-heat operation)...if the warning lamp is on for too short time it might be wrong ECT input, you can check that too by unplugging the ECT sensor(in the coolant elbow) and measure resistance across the sensor's pins an compare with the real ambient gtemp based on the attached resistance table, if the value is way out of whats should be put a new sensor(use genuine LR or at least Bosch not very cheap aftermarket)