I drive an old Daihatsu Charade 1993. Just 2 days ago, I heard a bubbling sound from the coolant when I turned off the machine. I didn't really care much until yesterday when the car got hot abnormally (3/4 of the gauge, usually 1/4) while idling, though the heat did lessen when the car moving, but it does imply the car has a trouble. Looking back, I guess it has something to do with the bubbling noise I had heard.
When I checked the coolant container I saw the liquid is still at just below max level which is fine, no leaking on the ground as well.
I drove again this morning, the car didn't get hot and I didn't hear the bubbling anymore, so I thought there wasn't any severe problem (I might be too optimistic). However, that symptom came back again just now when I drove for around 10 minutes. This time I noticed the coolant level got even higher, I still don't have any idea why, but surely it wouldn't be the head gasket thingy since I saw no leaking at all.
Now, as I did some research, there is a tendency saying this is a problem with the radiator cap being melt down or not being pressurized enough, but I'm not sure if it exactly is the case.
I think it'd be better to ask on here before bringing my car to the mechanic so I know the scope of the problem.
Please help if you know, any guesses would do.