yeah like the topic says it's for a CRX

 

Won't hold the pressure in the system and will lead to cooling problems.
The system is pressurized so the coolant can rise above boiling point.
If the pressure can't hold, the coolant can't get as hot so it can't absorb as much heat? Someone correct me if i'm wrong.

 

yep your pretty much right. It needs to be pressurized, so the system can reach and stay a certain temperature.

 

if the cap isnt good you can have boiling coolant without the temp gauge rising