1.5D losing coolant

[Jonathancilia]

Hi, my saxo i noticed recently has been losing coolant, about half a litre or abit more every 3000 miles. I don't see any leaks anywhere, thought it is maybe the expansion tank cap, can see small residue near the cap but nothing that says half a litre leaked out. Also, the expansion tank should be filled to the top of the red mark inside of the tank right? The car has 115k km on it, serviced every 3000 miles and coolant changed every 2 years.. its a well taken care of car, no loss of power nothing. Radiator expansion tank cap was replaced once but that was iirc at 70k kms

[Chipwizards]

If you pressurise the colling system and leave the car overnight you will probably see where the water is going.

[Jonathancilia]

I believe i found the problem as i said about the cap, today drove a long drive to heat up the coolant and i can see water near the very small hole of the expansion tank (next to the cap) i will replace the cap and see if problem goes away