I'm battling an
overheating problem with a 2002 Thunderbird with just over 105,000 miles. What I find strange is the car overheats at highway speeds, 45 to 70 MPH, at ambient temperatures as low as 70°F after about 10 to 15 minutes of driving. At an idle with
AC running the car doesn't
overheat even at temperatures above 95°. The hydraulic cooling system was removed, due to a leaking pump and high pressure hose. It was replaced with a Flex a Lite 183 electric fan mounted inside the original fan shroud. The degassing bottle was replaced due to stress cracking along with a new
thermostat, 183°F. The
thermostat was replaced twice with a two different brand names (also tested in boiling water). This didn't solve the
overheating problem. The
original radiator was replaced with a new
radiator, new
water pump, and new hoses. Made no difference. The cooling system has been maintained, flushes every 40K. The air flow through the
AC condenser, transmission, and
power steering cooler is clean, no blockage and all the baffles are in place . The car was checked for a blown
head gasket and the back pressure was 0 PSIG on both
catalytic converters. The system pressurizes and doesn't lose water and the heater works very well. At an idle the temperature runs at 210 to 215°F. At a cruise it climbs to above 245°F. If I place the car in neutral and coast the temperature will drop relatively quickly. Running the engine with no load at 1500 to 2000 RPMs, with an external booster fan, the car will
overheat in about 15 minutes, (Flex a Lite fan running full power). Temperature was measured using an external probe also indicated excessive temperatures.
Radiator is dropping about 40 to 45°F from inlet to outlet. Any thoughts or advice would be very much appreciated.