an even easier way...
is to use one of the hydrocarbon sniffers. Buddy of mine with a shop has one, simple to use, open radiator cap, run engine a few minutes, place sniffer over the radiator opening and if there's a head gasket leak, the sniffer will sound. It picks up on the hydrocarbon gases being forced into the coolant. Personally watched it in action on a blown Isuzu head gasket.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.