I would guess to bleed out the air in the system when you fill it after loosing fluid or after changing or flushing the system.
To replace a thermostat on a 2000 Ford F-250 V10, drain the radiator. Locate the thermostat on the top hose assembly and remove the screw. Replace the thermostat and refill the radiator.
Follow the upper radiator hose to the engine. It is clamped onto the thermostat cover. There should be a coolant bleed screw just above it. 3.1L engine.
Follow the TOP radiator hose to the engine block Remove the hose from the engine block. Thermostat should pop out. Some screw in, most pop out.
follow the top radiator hose down to the enginge and gently remove the two screw bolts holding the housing to the engine.remove the housing. The thermostat can then be removed by hand.
Disconnect negative battery terminal for your safety. Follow directions to remove the upper radiator hose. Inside the metal pipe on the engine where you removed the hose, is where you will find the thermostat. You will need a 10mm socket with an extension arm to remove the two bolts. Pull out the thermostat, noting it's position, and push in the new thermostat with new gasket attached and screw back together. Replace hose and refill coolant.
Not sure what year you have but on my 1984 its on top of the engine. Under the dome at the end of the radiator hose. There are 2 bolts that have to be removed in order to get to the thermostat. On a 1998 model, follow the top radiator hose to the engine. The hose attaches to an aluminum elbow with a brass slotted screw on top (the slotted screw is loosened to let air out of the cooling system). Remove the two bolts to take off the aluminum elbow and there will be your thermostat.
the thermostat is located in the housing where the top radiator hose enters the engine. Note: there is also a brass screw on the top of the housing, this is to bleed the air from the cooling system when you replace the thermostat (or do other cooling system repairs)
Because you need to bleed the cooling system. You should have a plastic bleeder screw right beside the radiator cape that you need to remove and let the air out, while filling the radiator. Do this while warm to make sure the thermostat is open.
There is a thermostat mounted to the radiator (left side); you merely unscrew it after disconnecting the electrical plug. Screw the new one in (along with a new washer) and reconnect the plug. To replace the thermostat inside the water pump: Drain the coolant; remove the lower radiator hose flange from the water pump housing; pull the thermostat out; install new t-stat and seal; reinstall the flange; fill system with coolant/anti-freeze.
Its underneath on the passenger side , first you will need to take of that plastic shield under the front bumper by loosing a dozen of 5 mm screws and one 10 or 12 mm screw , as soon as you take that shield off , you will see a the metal room connected to a rubber join coming from the radiator , this metal room has 2 8mm screws you will need a universal joint to loose the back screw , after you take out this part which will still attached to the rubber joint you will see the thermostat take the rubber casket and then just pull the thermostat out
Where the top radiator hose meets the engine there is a small hemi spherical housing, the thermostat's inside. The brass screw on top of this housing is where you bleed the air from the cooling system after replacing it and refilling the system. Be sure not to overtighten it after you screw it back together or you can snap the top off of it (brass is soft)
the thermostat on the 94 lesabre 3.8 is on the left front of the engine. the top radiator hose runs to it and it should have a screw on top(this is for bleeding out the air when refilling the system. it is kind of round and has two bolts holding it down. be sure to replace the asket when replacin the thermostat