plain OM· Registered
Coolant should not leak out from around the radiator cap. When the pressure in the engine increases, excess coolant should be released to the external reservoir. If it's coming out around the radiator cap, the hose to the reservoir might be blocked or the radiator cap is defective.Coolant was leaking from around the radiator cap.
If, the overflow hose to the reservoir is blocked, or the rad cap is defective, as the car heats up, the excess coolant is lost (as was evident -- leaking around the cap) and won't be recovered as the car cools, leaving the contents of the radiator down by what was lost.
I'd start by checking the hose to the external reservoir, making sure it's not blocked, that the bottom of the reservoir isn't full of accumulated "gunk", and that the hose fits snugly on the nipple just below the radiator cap. I'd also inspect the rad cap to be sure the rubber gaskets are intact and that the cap is locking down fully on the radiator neck.