Rep Power: 0

The original Reservoir caps that come with the car have this little rubber or paper circle tucked neatly on the inside of them. I assume this helps keep pressure from escaping and air from coming in, but i'm not sure.
Well my car has a loss of coolant that i am actively working on and i do keep an eye on my coolant, but twice now iv slacked off and ran a bit hot and i had to stop driving to cool down.

Both times this has happened, its melted or morphed the shape of that little circle in the reservoir cap. The first time was pretty bad and i noticed the spots where coolant was clearly coming out of the cap. I went to the junkyard and found myself another factory cap off another 6th gen civic and replaced the entire thing.

Now this has happened again and im noticing the same problem, but i want to know how i can replace this piece in the res cap or maybe jerry rig it with something so i dont have to go get a whole nother cap. I've noticed the cap autozone sells doesnt use anything like this on the inside, so i may just have to get one of those?

 
Rep Power: 211

Get another cap from a junkyard. My guess is that the reservoir doesn't hold pressure: https://www.aa1car.com/library/coola...ry_systems.htm
Possibly, can form your own with this: ,,,,,Autozone sells it.