Mazda 626 overheating

If not losing any coolant , could be faulty engine coolant temperature sensor .

on closer inspection im losing fluid from the coolant resevoir it appears to be coming out the top of the resevoir as the sides are damp to the touch i guess it maybe boiling up in there .ive checked the hoses and when i squeeze them they bounce back

if the engine coolant temperature sensor was faulty would that mean that the dash gauge would give wrong readings ? as it is the gauge goes off the scale to hot at whick point i pull over and allow the fans to bring temp back down to normal ?

my car overheats (the temp gauge skyrockets all the way to hot) ONLY when driving. when it is idle, it can sit there all day running and not go past normal. we have speculated it could possibly be the water pump or thermostat but are not sure. the fans are working fine during idle and driving so that doesnt seem to be the problem however the temp only goes up to dangerous levels (at least by the gauge) while the car is actually in motion for a few minutes. after parking it and leaving it idling it drops down to normal again. can anyone help or give any insight on the issue?

If you are losing coolant from header tank , it sounds like it's pressurising .It could be head gasket . If you get a sniff test (block test ) done it will let you know if this is correct or not .