Seat leon "overheated"

[81ash]

The garage sound useless, whilst it might be difficult for a DIYer to categorically test, a garage should have the equipment on hand to test it much better.

As for Radweld, its normally safe for nearly all engines (even rover engines - unless you have the KV6 engine 2.7, which it was'nt suitable for due to the narrow waterways). That said your usually better to try a long term fix for the problem, i recently had a tiny weep from my around around the fan switch, rather than drain the whole system to replace it i used a bit of radweld in the system which cured it.

[the_grafter]

sounds like air blockage mate drain all the water system down refill etc and then check again