Radiator help......

Not sure what that is stuck in your radiator. Possibly a Vinegar Flush on your radiator and cooling system will break that stuff down so you can drain it out.

Look up on Google: How to flush your cooling system with vinegar. So you can learn how to properly do it.

Don't use vinegar with aluminum radiators and aluminum heads.

Can take the radiator out and turn it upside down and back flush it.

Then turn it right side up, put the garden hose in the top, the water should flow out the bottom exit just as fast as it is going in the top . . for a properly working radiator.

There also used to be an old radiator fix called "Rodding them Out" where a radiator shop pulls one of the tanks off and runs a wire down through each of the cores to get the lime deposits out. Then they resolder the tank back in again.