I recently bought a new GM radiator ($277.00 dealer cost) and am planning on sending my old one to Nick to let him work his magic on it. Here's something I did that really lowered the coolant temps. I used distilled water, 8 ounces of RMI-25, and a bottle of Redline water wetter. I was running temps around 193 with the A/C on and the outdoor temp of 90 degrees. Now it's running around 175.