Engine Cooling System problems of the 1997 Ford Explorer Sport

I had taken my vehicle to the dealership on three separate occassions due to coolant loss and the temparature guage reading cool. On each occassion they replaced the thermostat. The last time was just prior to the expiration of the extended warranty. I specifically requested that it be tested and checked thouroughly becasue I did not want to replace an engine after the warranty expired. They replaced the thermostat. Shortly after I experienced the same difficulty. I took the vehicle to a private garage and they reported that the head gaskets had failed and were leaking. I contacted the service manager at the dealership and he requested that I bring the vehicle to them for tests. Several days later the service department called and informed me that the head gaskets had failed and that coolant was entering the cylinders. They offered to replace the engine for $4600. 00. Not going to happen.