I have no heat unless the car idles for
Before even trying a new thermostat, try blocking air flow past the radiator and engine area with some cardboard in front of the radiator. If your temp. gauge shows below half all the time, try a hotter rated thermostat, one that stays closed just a bit longer. Say your t-stat is rated at 190 degrees, get one that is rated at 193 degrees- do small raises to avoid overheating-and in the summer, you may want to go back to the lower rated t-stat.. A parts store or Ford dealer could help you pick an optional thermostat.
To replace, drain enough coolant from the radiator so the level in the engine is below the thermostat housing. Take off the upper radiator hose from the thermostat housing. remove retaining bolts or nuts from the housing, any other obstructions, and pull the housing off, replace thermostat, clean the gasket mating area on the housing and the engine block, use a new gasket and fit all back together. Careful not to overtighten the t-stat housing bolts: the torque specs would be small-about 15-20 foot pounds of torque-just snug them down good-you can always go back and re-tighten a little if you see a leak. So, all back together, refill coolant and overflow tank, run engine with radiator cap off till engine is hot, and thermostat opens-this will helpyou bleed air out of the system. When thermostat opens, coolant level should drop a little. Shut off the engine, top up radiator and overflow tank as necessary, and replace radiator cap. Check for leaks.