hi i have a k reg vauxhall cavalier LS now i took it for MOT yesterday and it flew through no problems at all ,,the thing is if i am ticking over for ages i have noticed today that my fan doesn't come on ,,,however the fan has been tested and does work + the temp gauge on the dash also works fine so why is it that the fan doesnt come in to action when it starts to get hot ,,,i'm not well up on vauxhalls do they have a sender unit and if so were is it ? or what else could the problem be ..thanks