I have a 1948 MK V that had overheating problems. A friend suggested using Evapo-rust. I drained the coolant, flushed the system twice with water, then filled the system with Evapo-rust that I ordered from Home Depot, $80 for a 5gal pail. I ran this for a month using the car every day. Each day I noticed the gauge being lower. Once it was running normal, I drained the Evapo-rust back into its pail to use later in another vehicle. I then flushed twice again today and filled with antifreeze. It works great, No overheating now at all! Evapo-rust does not eat aluminum, gaskets or effect the water pump.
I highly recommend this product.