You can't build up enough water pressure to blow a head gasket. The cooling system won't be the cause. To check the quench you put a small chunk of clay on the top of the quench dome of the piston and set the head back on the engine with the gasket. Bolt it down to squeeze the gasket.Manually turn the engine over at least one full rotation to make sure the piston has reached to TDC. Pull the head back off and measure the thickness to the clay. Use feeler gauges on top of the quench dome next to the clay to equal the height of the flattened clay. That's the amount of quench space you have. I use a drop of oil on top of the clay to keep it from sticking to the head and ruining your measurement.