Adding Coolant

[Cassidy SC]

I need to add more coolant to my 92 SC but the cap on the surge tank is tight as hell. I removed the black cap on the tank but i see there's another cap underneath it and thats what i can't remove. I dont wanna take it in for service because i dont feel its necessary yet if all i need to do is add more coolant to the surge tank. Does anyone know a specific tool that I can use to get that tight son of a bitch off? Any suggestions would be much appreciated.

[gt50]

There is only one cap. I think you broke your cap in half trying to get it off.