Let it run in the driveway for 20 minutes, shut it off and look for
leaks. Or better yet, drive it for 20 minutes, let it idle in the drive
for 5 minutes and shut it off before looking. If you see no leaks,
chances are good you have a bad head gasket. The tail pipe may be wet
and white smoke may be seen too. Any decent shop can do a simple
pressure test on the system and tell you where it's leaking.