ace rimmer

went out to a cruise last night after sitting on idle for half hour it started to belt out lotts of steam from the exaust so i reved the engine and more steam came out (so i'm thinking head gasket by now) so i drive home and as soon is i start to drive the steam stops, expected as the presure in the pistons increases but i expected the water system to presureise or over heat witch it did'nt.i took it in to my work today and gave the usual a once over and everything is ok no loss of water, oil is clean so let the car idle fo a while and no steam and the car drives just as normal so what you's thinking? any info will be brill guy's p.s its running 15/16psi is that ok?