Do I have a bad head gasket?

This was something I learned when I wrenched on cars. No T-stat and put air into each cylinder just like leaking a motor down and look in the radiator. Bubbles will be present and a backdoor way of pressure testing. I did this when I suspected a head gasket but the usual techniques weren't working. Just something else to try if you suspect a leakage and easy to test....

JW