coolant bottle full..radiator low

hi..
After a good 300km drive yesterday ,i checked under the bonnet this morning and straight away noticed the coolant reserve bottle full ..and checked the radiator and it was low ..there,s nothing obvious thats causing this ,could it be radiator cap ?...........about 3 weeks ago jimny overheated badly it blew the cap off the reserve coolant bottle because alt belt snapped and i didnt notice until it was running like a pig and seen temp maxd out ,..seems to be running ok since new belt ,there,s no water in oil etc,...any thoughts or ideas on fixing this would be appreciated ..thanks

Sounds like head gasket failure/warped head.

Top the radiator up fully, and see what happens, on the off chance that there was an air lock last time.

And check for leaks from the radiator and heater.

Is the pipe that dangles into the over flow bottle still on? If thats fell off it the coolant will not return as the radiator cools down.

thanks for the replies ,
i hope its not head gasket leakage but seems probable ,i looked for air bubbles in radiator today ,none there and also checked under oil cap for water marks and checked dip stick again ,seems ok could be a tiny head leak but i hope not ,all hoses and reserve bottle hoses are on and seem ok ,ill just keep a close eye on everything and see how it goes ..ill buy a new radiator cap as it looks very old ..any more ideas would be appreciated ...
thanks

Looks like cylinder head gasket failure and warped head.( in this case the cooling system is being pressurised) A cylinder leakage test will confirm this 100% for you .

Steve.

thanks Steve
im going to wait a week and see how it goes .hopefully there was some air hiding in there or something similar ,ill get the pressure test done if it continues ,if it is the head i might have a go at it myself im a bit concerned about the expense in paying someone to do it ..
thanks