Buy Nissan Altima Engine Coolant Thermostats

The thermostat sits inside the outlet housing where the upper radiator hose meets the engine. It stays shut while the block warms, then cracks open near 180 °F to let coolant flow to the radiator, stabilizing temperature around 195 °F. (J.D. Power, Nissan Club)
On QR25DE engines a second water-control valve opens about 200 °F to manage head temperature during heavy loads or hot weather. (Scribd, SCANNERDANNER)

• Valve-opening window (main): 80.5 - 83.5 °C (177 - 182 °F) with full lift by 95 °C (203 °F). (Scribd)
• Water-control valve opens 93.5 - 96.5 °C (200 - 206 °F).
• Coolant capacity (2.5 L Altima): ≈ 8.6 qt including reservoir.
• Housing-bolt torque: 7 - 8 ft-lb (≈ 11 N·m)-finger-tight plus a quarter turn. (Nissan Club)
• Common code: P0128 signals the engine is running cooler than expected, often from a stuck-open thermostat. (Kbb.com)

• Temp gauge spikes or drops-needle jumps to H or stays cold. (J.D. Power)
• Weak heater output even after warm-up. (Altima Forums)
• Coolant puddles or crust around the housing gasket. (J.D. Power)
• Erratic fan cycling or boiling sounds in the radiator.
• Long warm-up plus poor MPG-the engine never reaches closed-loop temperature. (Kbb.com)

1. Let the engine cool completely; relieve pressure by loosening the cap.
2. Drain about one gallon of coolant from the radiator.
3. Remove the air-intake duct for clearance.
4. Unbolt the thermostat housing (three 10 mm bolts).
5. Lift out the old valve; note its jiggle-pin (install new unit with pin up).
6. Clean the mating surfaces; fit the seal ring on the new thermostat.
7. Torque bolts to 7-8 ft-lb and reconnect the hose. (YouTube)
8. Fill with premixed long-life coolant; run engine with heater on high, topping up until bubbles stop. (J.D. Power)

• Flush coolant every 60 k mi or 5 years, whichever comes first, to prevent mineral deposits from jamming the valve.
• Watch for code P0128 after long downhill trips in cold weather; a quick reset is fine if the code doesn't return. (JustAnswer)
• Keep an 8 mm hose-bleed port clear (where fitted) to purge air pockets that can mimic thermostat failure. (YouTube)

A sticky thermostat can mask-or be caused by-other cooling issues:

• Radiator cap with weak spring may vent too early. (Scribd)
• Cooling fan relays/sensors that run the fan continuously can prevent the thermostat from reaching full temp. (Kbb.com)
• Clogged heater core often produces "no-heat" complaints even when the thermostat is fine. (YouTube)

Running below design temperature forces the engine computer to enrich the fuel mixture, lowering gas mileage and raising tail-pipe emissions. Replacing a faulty thermostat can restore up to 10 % fuel economy and help the catalytic converter last longer. (Kbb.com)

Q: How many thermostats does a 2.5 L Altima have?
A: Two-a primary thermostat in the housing and a secondary water-control valve on the cylinder head. (CarGurus)

Q: What temperature should my gauge show once the car is warm?
A: Between 190 °F and 210 °F (about the middle mark). (Nissan Club)

Q: Can I drive with code P0128?
A: The car will run, but it will waste fuel and may damage the engine over time. Replace the thermostat soon. (Kbb.com)

Q: Why is my heater still cold after I changed the thermostat?
A: Air trapped in the system or a clogged heater core can block hot coolant flow. Bleed the system and check hoses. (Altima Forums)

Q: Do I need special tools?
A: Basic sockets, a drain pan, and a small torque wrench that reads 7 ft-lb. (Nissan Club)

Q: Which coolant should I use?
A: Use a silicate-free, long-life antifreeze that meets Nissan blue/green specs, mixed 50/50 with water. (Scribd)

Q: How often should the thermostat be replaced?
A: There is no mileage schedule; change it whenever it sticks or during major cooling-system work. (J.D. Power)

Keeping the thermostat and cooling system in top shape ensures smooth performance, better fuel economy, and long engine life for your Nissan Altima.