consueloscott1972, try this:"
Before servicing the vehicle, refer to the Precautions Section.
Drain the cooling system.
Disconnect the negative battery cable.
If equipped with an engine undercover, remove using a power tool.
Remove drive belts
Remove water drain plug on water pump side of the engine.
Disconnect lower radiator hose.
Remove engine coolant inlet and thermostat assembly.
NOTE
Do not disassemble engine coolant inlet and thermostat. Replace them as a unit, if necessary.
To install, reverse removal procedure.
NOTE
Install thermostat with jiggle valve facing upward.
Fill the cooling system.
After installation, run engine for a few minutes and check for leaks.
From [http://www.autozone.com/autozone/repairguides/Nissan-Car-Altima-Sentra-1999-06/Thermostat/Removal-Installation/_/P-0996b43f80381f1a#hd1-1-6|here.] Hope this helps, good luck.
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