head gasket leak

Do a compression test...

With the engine warmed up, remove all spark plugs and prop the throttle wide open, crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 psi. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.

Be sure to use a compression tester with a screw in type adapter. The other kind of test adapters are unreliable.

In addition to the above tests, pressurizing the cooling system may give you some indication where the leak is occurring - sounds like you have multiple problems. Any coolant in the oil? Any vapor out the tailpipes that smells like antifreeze (sweet smell) when the car's running?