If it is electrolysis the problem is caused by stray current. If it is galvanic corrosion, that is caused by dissimilar metals. Both situations will eat the aluminum, which is low on the galvanic scale. Both can be treated with an anode. I suspect you have galvanic corrosion, not electrolysis. If you disconnect the battery do you still get the radiator building pressure? What time frame are we talking about to build this pressure? If you still get the phenomena with the battery disconnected you have galvanic corrosion. If you only get the effect with the battery connected you have a current leak somewhere (which I suspect is not the case).

Frequently people use the term electrolysis when they really mean galvanic corrosion. Cavitation and ventilation are frequently misused also, people call ventilation cavitation and they are very different. Boy, am I sounding like a pedantic engineer (which I am).