How to replace thermostat
The procedure is fairly generic on the Ford and other non-transverse engines. First think of direction of coolant circulation. In radiator, coolant flows under gravity (and negative pressure as will be seen) to the bottom radiator hose and through it to the intake of the water pump. (The pump is directly aft of the fan with the vibration damper and accessory belt drive pulley sheaves in between.) The pump then forces coolant through a port into the engine block and galleries; and also force coolant through the heater coil circuit which returns it (also) to the engine block. Under pump pressure, the speed of which is governed by engine RPM (crank rotational speed), the coolant circulates back through the coolant pump via a second engine block port until (like an 8 track tape)...until the coolant has heated (by combuston chamber heat sinking) to t'stat (thermostat)-regulated engine-normal-operating temperature, at which point the coolant flow though said engine bock recirculation port abates and is supplanted by coolant flow through the t'stat and out the engine and back to the radiator (inlet) through the upper radiator hose. So it's clear then, that where the upper radiator hose joins the engine block (near the top of the engine) there also will be the thermostat, held in place by a connector fitting or fittings to which the upper radiator hose couples on one end, and which bolts onto an engine block outlet port and flange on the other end. At that point, it is a simple matter of unbolting that coolant flow port fitting to find the t'stat squeezed in and concealed behind. Of course, you will want to have let the engine cool (to the point where upper radiator hose is squeezable), and to have disconnected that upper hose from the radiator and held it aloft to reduce spilling and then lowered to capture any spillage. (The engine having cooled, the t'stat will be closed and preventing any outflow into the hose; and the cool engine block coolant level will have have retreated under gravity to its lowest level...below the t'stat. Now that the t'stat has been removed from the hose connection flange, you will have noted beforehand its direction and orientation top to bottom...because the new t'stat must fit in the exact same manner. In case you overlooked it, those are also embossed on the new t'stat. Now remember this: each new t'stat must be installed with a new overlap seal ring, but WITHOUT any other sealant or gasket sealant material (the seal is not a gasket despite what you might read or see) and its overlap of the t'stat forms a double seal layer sufficent to contain and prevent any coolant seepage. So, now that you've clamped in the t'stat with the hose fitting and restored upper-radiator-to-engine-block hose connection, you need only to pour any captured coolant back into the radiator, screw on the radiator cap, start the engine, and bring to operating (t'stat open) temperature. Then relieve radiator pressure with radiator cap and note that coolant is circulating in the radiator. If not yet circlating, wait a while until the new t'stat opens. Finally, after engine off and cool-down, check and top the coolant level to about 1 inch below bottom of radiator filler tube.
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