Engine Coolant Overflow

[i_am_oasis]

Good morning Automotive Forum,

I own a Cavalier Z24 with 146000 Kms. It's been serviced regularly and up until now has been in good shape.

Over the past week, I noticed that my car will expel engine coolant from the overflow line (at the top of the collant reservoir). This has happened twice now in the past week and it always happens after a 10 minute ride. I'll shut the car off, and all of a sudden it just vomits out of the overflow line.

I added a bottle on the end today and went for a 2 minute car ride. I saw that there was some coolant (maybe a few tablespoons at most) inside the bottle.

Does anyone know what could be causing the problem? I've heard that it could be anything from a replacement cap to a head gasket. Would you recomment I get a pressure test to diagnose this?

Thanks in advance,
Steven