Race only electric water ?
It sounds like something is getting pressurized from the crankcase somehow and it's causing the problem.
I'd get the car on the dyno , and make a n/a pull with it and see if you have the same issue. How is your overflow set up? Try warming the car up, once everything is up to temp drain all the water out of the overflow, and try either making an n/a dyno run or an n/a run down the track, and check your overflow. If the overflow is full of water, then you have a head gasket that is done.
If that works, then try it with the juice on but I'd make a 1/2 track run for the first one, no need to get water all over the tires and wreck the car!
fwiw I run my radiator about 2 to 2/5 inches down from the top, and I never get any more then a drop in my overflow during a pass. You could just have the system too full, overflow too full if it's a recurcilating setup (mine is not)





