What test to perform to make sure:
• The first is a carbon dioxide test performed on the cooling system will tell you if C02 is going inside your coolant.
• A leakdown test will allow you to check each cylinder to look for pressure loss inside the cylinder. Failing the test could also be seepage past a bad valve guide, piston ring...
Head Gasket Testing Kit
The best method is to have a service shop, or a friend who owns a block test kit test your system for a compression leak to your cooling system. I heard that some test kits can be purchased from auto stores. This is a test unit and test fluid that changes color with the presence of exhaust gas in the engine coolant. Another test that should be completed is a coolant system pressure test Test your system for leaks with nine to twelve Psi pressure. It should not show any appreciable pressure loss within 5 minutes.
Sometimes it's worth it just to have a pro shop diagnose the problem, even if you are planning to do the repair yourself.