05 MINI Cooper Overheating Problem

[Revs_Addiction]

My mum has one of the above, and after a run round the M25 this evening, it overheated big time...

She got taken home by the RAC who diagnosed a thermostat problems because, 'the rad was cold'...

Can anyone explain this to me? In my mind, if the car is overheating whilst the rad is cold, that would point more to a water pump issue, kinked or blocked rad pipe, or airlock?

Coolant system was pressure tested a couple of days ago and given a clean bill of health, although a broken rad cap was diagnosed and replaced, (car had not overheated at this point, but rad fan was very noisy - prompting her to put it in the garage for a check), apparently RAC man didn't need to add much when topping up coolant...

Apparently RAC man said the engine sounds okay, so hopefully no major damage has been done, but does anyone have any clues or ideas what else could be wrong, as I don't want her getting shafted by the local garage she insists on using...

Cheers all...

[davepoth]

Thermostat is quite a likely candidate. The cooling system is designed not to flow water to the radiator unless it's warmed up, since otherwise the engine would not be warm enough to work properly. Thermostats can go bad with age.

[Zoobeef]

Simple test is to put the thermostat is a cup of boiling water and you'll see it open if its not broken