Mopar (Autopar) antifreeze from the dealer, mixed 50:50 with distilled (or deionized) water. I got about 5 to 6 years out of a radiator changing antifreeze every other year when using Prestone. Since switching to Mopar antifreeze, my factory two-core (towing package) rad on my 1990 lasted until 2003, when a seam split. My wife's 1994 car still has the factory rad-- Mopar antifreeze works! A nice way to avoid getting air in the block is to install a Prestone-type flushing T in the heater hose. You can then flush it out with a hose, then refill as per instructions with the T. This avoids the trapped- air problems and having to pull the temp sensor at the back corner of the engine to burp the air. 4xBob