I run a SBC with alu heads and for the past 12 years I have circulated water thru the heads with a pump (fuel pump extention) and have never had to surface the heads. On first fire up with the tank cap off if chec the water level after I depress the spit valves at the back of the heads to make sure water has completely filled them. The tank is only filled 2/3rds to allow for expantion.
Water expands when heated and steam pressure rises past the point of 3# and the check will pop off. Early racers using the HEMI would tap into the water fill bosses to direct water expantion into the headers. water pressure was not too much a problem since the cars fired-went to the line-raced. With the added burnout,more heat developed quicker,so a check was added and plumbing into the headers was a easy deal since cars were still using standard breathers.
Temp gauge on the bottom to monitor warm-up heat and fuel system rich/lean (cyl head heat)
