Coolant Overflow Bottle Keeps Running Low

[REDGTT]

I lose about 1 centimetre of coolant through the overflow a day. And I cannot find the leak.

No the bottle has not been overfilled.

The bottle has been taken out and no cracks or leaks.

Checked under the car for leaks and cannot find any.

Checked around engine bay and no leaks

Checked Radiator and the coolant isnt leaking from there and there is no sludge nor air bubbles suggesting a blown head gasket.

Checked inside car and no leak from heater box or firewall

Would it be the the radiator cap? If it was wouldnt I notice some coolant around there or does it just hiss out and evaporate?

Thanks ahead.

[Bl4cK32]

I have the same problem (see down a few topics)

Ive narrowed it down to either - radiator cap, or a tiny leak somewhere.

replace the cap, then get a pressure leak test done at a radiator place.

See if they work, then report back

[REDGTT]

Ok will do. Might save alot of other people later on heart ache.