Mercury F5DZ-8575-A Thermostat Assembly

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Don't drive the vehicle without a thermostat! The engine may not reach the required temperature for the computer to go into closed loop operation and emissions and fuel economy will suffer. Before condemning the thermostat, check the coolant level, drivebelt tension and temperature gauge (or light) operation. If the engine takes a long time to warm up, the thermostat is probably stuck open. Replace the thermostat. If the engine runs hot, check the temperature of the upper radiator hose. If the hose isn't hot, the thermostat is probably stuck shut. Replace the thermostat. If the upper radiator hose is hot, it means the coolant is circulating and the thermostat is open. If an engine has been overheated, you may find damage such as leaking head gaskets, scuffed pistons and warped or cracked cylinder heads. The same tool that many shops use to check for combustion hydrocarbons in coolant, which indicates a head gasket leak, is available at local auto parts stores. To replace the thermostat, drain coolant from the radiator until the level is below the thermostat housing. On 1998 and later models, remove the plastic cover over the top of the intake system for access to the thermostat. On some models of the OHV engines, it may be necessary to remove the distributor cap in order to remove the thermostat housing. Disconnect the upper radiator hose from the thermostat housing and the bypass hose from the thermostat housing on OHV engines. Remove the vacuum switching valve attached to the thermostat housing and disconnect the vacuum lines before removal. Remove the bolts and lift the cover off, tapping it with a soft face hammer if necessary. Remove the O-ring seal on an OHC engine. Note how it's installed, then remove the thermostat. Use a scraper or putty knife to remove all traces of old gasket material and sealant from the mating surfaces. Install the thermostat with the correct end facing out, directed toward the engine. Apply a thin coat of RTV sealant to both sides of a conventional paper gasket and position it on the engine side, over the thermostat. On models that use an O-ring seal, install the new O-ring into the intake manifold. Carefully position the cover and install the bolts, being careful not to over tighten them. Reattach the radiator hose to the cover and tighten the clamp. Refill the system, then run the engine and check carefully for leaks. Repeat the steps to be sure the repairs corrected the previous problem(s).

Before blaming the thermostat for cooling issues, check the coolant level, drive belt tension, and temperature gauge. For thermostat replacement, disconnect the battery cable, drain the cooling system, and find the thermostat housing. Detach the hose and the thermostat.

Don't drive the vehicle without a thermostat! The engine may not reach the required temperature for the computer to go into closed loop operation and emissions and fuel economy will suffer. Before condemning the thermostat, check the coolant level, drivebelt tension and temperature gauge (or light) operation. If the engine takes a long time to warm up, the thermostat is probably stuck open. Replace the thermostat. If the engine runs hot, check the temperature of the upper radiator hose. If the hose isn't hot, the thermostat is probably stuck shut. Replace the thermostat. If the upper radiator hose is hot, it means the coolant is circulating and the thermostat is open. If an engine has been overheated, you may find damage such as leaking head gaskets, scuffed pistons and warped or cracked cylinder heads. The same tool that many shops use to check for combustion hydrocarbons in coolant, which indicates a head gasket leak, is available at local auto parts stores. To replace the thermostat, drain coolant from the radiator until the level is below the thermostat housing. On 1998 and later models, remove the plastic cover over the top of the intake system for access to the thermostat. On some models of the OHV engines, it may be necessary to remove the distributor cap in order to remove the thermostat housing. Disconnect the upper radiator hose from the thermostat housing and the bypass hose from the thermostat housing on OHV engines. Remove the vacuum switching valve attached to the thermostat housing and disconnect the vacuum lines before removal. Remove the bolts and lift the cover off, tapping it with a soft face hammer if necessary. Remove the O-ring seal on an OHC engine. Note how it's installed, then remove the thermostat. Use a scraper or putty knife to remove all traces of old gasket material and sealant from the mating surfaces. Install the thermostat with the correct end facing out, directed toward the engine. Apply a thin coat of RTV sealant to both sides of a conventional paper gasket and position it on the engine side, over the thermostat. On models that use an O-ring seal, install the new O-ring into the intake manifold. Carefully position the cover and install the bolts, being careful not to over tighten them. Reattach the radiator hose to the cover and tighten the clamp. Refill the system, then run the engine and check carefully for leaks. Repeat the steps to be sure the repairs corrected the previous problem(s).

Start by checking the coolant level, drivebelt tension, and temperature gauge operation.