1981 DL Wagon, 312K, my pressure cap on the coolant tank went bad and overheated on the way to work. I first thought the tank had a crack in it, but upon inspection it looked okay, then I figured out that the coolant was belching out the cap and it wouldn't build pressure in the system (hoses weren't firm.)

So I bought a new cap which fixed the pressure and leak problem, and ever since it misses on the #2 cylinder when cold. After a couple of miles and a little revving in gear it starts to run fine. But I've had to add coolant twice to an empty coolant tank.

Is this likely to be a head gasket or a cracked head/block?
--
Kenny H Two SUVs, four cars (three Volvos) and nine motorcycles