overflow

i have a rebuilt 250 less than 100 miles on it and a new radiator aluminum and it keeps overflowing and i have to keep adding coolant to it could it be because i dont have a fan shroud (its in a 77 nova 4door)

When I put an aluminum rad in my car, I found that the system expanded much more and ejected more water compared to the brass rad I had before.

If you fill the radiator up full when it's cold, it'll eject water when hot because the water is expanding and taking up more space. When everything cools down again the coolant level looks like it's low, but it may not be. It won't too full when the car is heated up again and it won't eject water.

This is why I'm going to replumbing my radiator overflow to act as a coolant recovery system to account for this and keep the radiator full at all temps.