I drained the radiator the other day. Then I refilled it. Now it wants to boil over so I have to let it cool down before adding fluid. What is wrong with it? Did I do something wrong?

1984 Delta 88

 

I think the problem is fixed. I opened the petcock and while it was draining, I put a hose in the top and let the water run. Then, with the water running, I closed the petcock and then shut off the water before recapping the radiator. After all that, I refilled the reservoir. If this works tomorrow, I will put the antifreeze back in.

 

you may have had an air pocket someplace in the engine block, air severely reduces the cooling capacity of a system. Hope you got it.