How many thermostats does a 2012 Nissan Altima have?
The 2012 Nissan Altima has exactly one engine coolant thermostat, regardless of whether it is equipped with the 2.5L four-cylinder or the 3.5L V6 engine. This single thermostat is the only coolant temperature-regulating valve in the engine's cooling system, and it is the component you need to inspect or replace when diagnosing overheating or temperature fluctuation issues.
The single thermostat and its housing assembly
On the 2012 Nissan Altima, the thermostat is typically integrated into a housing assembly that connects the engine block to the upper radiator hose. This is a single unit, not multiple thermostats working together. The official Nissan parts catalog lists two part numbers that relate to this one assembly: the thermostat assembly itself (Part Number: 21200-6N210) and the engine coolant thermostat housing (Part Number: 21200-JA10A). These are not separate thermostats; rather, they are the two physical pieces, the valve mechanism and the plastic or aluminum housing that holds it, that make up one complete thermostat unit. When you purchase a replacement, you will often receive the thermostat pre-mounted inside its housing, which simplifies the swap to a single-part replacement job.
Thermostat location by engine type
The thermostat's physical location is described in Nissan's service documentation as being within the "Engine Coolant Inlet Flange" or "Thermostat Housing." For the 2.5L QR25DE four-cylinder engine, this housing is mounted on the front of the engine block, near the upper radiator hose connection, making it accessible from above once the air intake ducting is removed. For the 3.5L VQ35DE V6 engine, the thermostat housing sits on the front of the engine, closer to the center of the block, also near the upper radiator hose. In both cases, the housing is a visible component with a coolant hose attached directly to it. You do not need to remove major engine components to reach it, though on the V6, the alternator or power steering pump brackets may partially obscure the housing, requiring a bit more maneuvering with your socket extensions.
How the engine coolant thermostat works
The thermostat in your 2012 Altima is a mechanical valve filled with a wax pellet that expands when heated. When the engine is cold, the valve remains closed, blocking coolant from flowing to the radiator. Once the coolant temperature rises to the thermostat's rated opening point, the wax expands, pushing a piston that opens the valve. Coolant then flows through the upper radiator hose into the radiator, where heat is dissipated. The thermostat continuously modulates between open and closed positions to maintain a steady engine temperature, only fully opening under heavy load or hot ambient conditions.
Why the confusion about multiple thermostats exists
Many online sources and forum posts incorrectly state that the 2012 Altima has two thermostats, with one dedicated to the cabin heating system. This confusion stems from a misunderstanding of how the HVAC system works. The cabin heating system uses a heater core, a small radiator located inside the dashboard, through which engine coolant flows whenever the engine is running. There is no separate thermostat controlling this flow; instead, a mechanical flap called a blend door, controlled by the climate control system, regulates how much air passes over the heater core before entering the cabin. If you are experiencing weak heat or inconsistent cabin temperatures, the problem is almost always a faulty blend door actuator, a clogged heater core, or low coolant level, not a second thermostat. This misconception is so widespread that it even appears in some owner discussions about home heating systems, where the reason for two home thermostats is entirely different, relating to separate zones in a house rather than a vehicle's engine cooling system. For your Altima, remember that the only thermostat you need to worry about is the single engine coolant thermostat described above.
