[SD1too]

I asked Lida to bring her car over to me this afternoon so that I could check the garage's claim that the coolant temperature sensor is over-reading and that consequently there is nothing wrong with the cooling system.

We correlated the displayed temperature and resistance of the sensor with the data in RAVE and they all matched. There was no error of the magnitude declared by the garage.

Strangely the bottom radiator hose was hot today, as it should be (previously it's been tepid). At Lida's last visit I refilled and bled the cooling system, leaving the level in the expansion tank at 'max'. Today, once again, the level had risen to the neck of the tank. I agree with Trikey that normally this is evidence of an air lock. However, the garage said that vacuum equipment had been used when refilling and I have subsequently drained, bled and refilled on two further occasions, so if it is an airlock it's the most stubborn I have ever encountered.

Although there is no reason to suspect the expansion tank cap, we decided to test drive Lida's car with my cap fitted. We began on local residential roads at 20 mph when the temperature remained in the low nineties. However, as soon as speed was increased and sustained at 30 mph on an 'A' road, the reading rose quite quickly to 99˚. As we continued it nudged above 100˚ and most strange of all, when returning to 20 mph over speed humps it was up to 107˚ then rapidly reducing to 99˚ in a matter of seconds, more quickly than fan action would achieve.
This is the same behaviour that Lida's observed with her own expansion cap fitted so we can eliminate that as a cause.

I learnt today that the garage obtained the replacement thermostat and pipes from a Land Rover parts supplier.

Simon