why am I over heating driving over 40 mph
my 2004 PT cruiser 2.4l turbo, over heats over 40 mph, let it sit at idle 1100RPMs go's right back to middle on temperature gauge. have flushed rad, changed temp sensor, thermostat, cap and high and low fan relays. the temp going into radiator is 180' and coming out at 140' when at idle or cooled down. HELP ???