Scotty, I have a 73 BMW 3.0 CS 6 cylinder. The car has been sitting for about 20 years. I got it started and it runs, however, I can't leave it running because the cooling system is blocked. The antifreeze is in the consistency of jelly and you can scoop it out with a putty knife, when I took out the thermostat. What would you recommend for getting this antifreeze out of the system? The radiator is clean. It must have been drained but they never drained the block. Thank you.

have it steam cleaned from inside by removing the hoses and the thermostat and shooting steam into the block to force the crud out