Any time l drive my car over 10 miles it cooks up. There was no ''event'' - no bang, nothing, it just started to run hot. Lexus changed the thermostat for £128! and it was okay on short runs. l drove 350 miles up the M1, fine. Coming back, just straight up into red. Now Lexus said it did not happen when they had the car but wanted £1100 to do the cylinder head gasket in case; as no oil or water was cross-contaminating, l thought I'd try elsewhere. Bosch centre could not get it to overheat either, but said the fluid coupling fan was not running. Next time l took it 15miles it cooked up. l drove it back at the top of the red and showed them. Having been switched off for a few mins before restarting, the fan was running, temperature plummeting. As they were at a loss, nothing has happened since. The car is in limbo - can not fix it, can not use it, can not sell it (except at huge loss). Does anyone Know how to fix this or where to start?

Scrap it.

WOW. Bosch really is bad at electronics. So far I've heard nothing, but bad things. l had my VW Passat is ABS Bosch made module malfunction. And so did many others, it is a actually a factory error, they made a whole line of cars like that! With faulty electrical boards! l would check up on this & see if u can find others like you, or in similar position. Try websites that r run by Lexus enthusiasts, forum boards, etc. i.e. like this VW one, vwvortex.com, so u have an idea. l found out what was wrong with my module on this kind of forums, then also found out how to fix it myself for an extremely low price! If this is an often occurring problem there will be third party companies that can help u out! Look into it. It will end up being much cheaper than dealing with the stealer-ships, & u will probably still get at least a 3 to 5 yr. warranty, depending who u deal with.

are you saying that the fan does not work occassionally?
have you checked the power supply to the coupling fan, and earth to see if cables are broken- transit might loosen a connection.. sorry can not be more specific. lexus not my model.
good luck.

Sounds like a faulty temperature sensor, easy to change.