Hi don't know if anyone can help, I have an 04 plate 1.4l petrol fiesta lx. It has started overheating when stuck in traffic or sat on the drive running. The temp gauge in the dash doesn't increase (reads normal temp all the time) and the first thing u know about it is steam coming out of the bonnet from the coolant reservoir. It's been in the garage and they can't get to the bottom of it! The fan isn't kicking in when it should. It has had a new sensor put in and isn't the fuses and relay they are working fine. The fan does work as when the mechanic ran a diagnostic test and it worked. This only happens when the car is sat idling. Has anyone experienced this before and if so can you help!? The mechanic is stumped at present and only suggestion is to send the ecu off to be tested.