not always that easy worked in a shop customer brought in tractor same deal pulled cooler off tested good so did head gasket. couple weeks later tractor came back oil in water what the heck so did the head gasket again thinking maybe the guy didn't do it right couple weeks later came back again ok test cooler tested fine again then some one came up with the idea use hot water or heated up the cooler can't member but the hot air or water was enough to open a crack in the cooler......needless to say it was a cooler the whole time this was at a red dealer and an experienced mechanic