I found lots of technical info at http://www.altimas.net/tsb/ Look at bulletin number NTB02-047. This explains how to troubleshoot poor heater performance and it gives a procedure for replacing the thermostat.
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To replace the thermostat on a 2002 Nissan Altima first drain out the coolant. Then proceed the to locate the thermostat housing which is by the engine compartment fuse box. Unbolt the housing and replace the thermostat.
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The 2002 Nissan Altima has 16 valves.
under the hood on the passenger side of the car on top of the alternator.
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The 2002 Nissan Altima is a gas-powered vehicle.
The 2002 Nissan Altima has an inline 4 engine.
The 2002 Nissan Altima has a 5-speed manual.
400.00
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The 2002 Nissan Altima runs on regular unleaded.
The 2002 Nissan Altima is 15 ft. 11.5 in. (191.5 in.) long.