How to Replace the Thermostat on a 300ZX

by Gregory Crews
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temperature dial image by Robert Kelly from

The coolant system in a Nissan 300ZX uses a thermostat to release coolant into the engine when it starts to get hot. The thermostat will close when the engine is operating under normal parameters. A sticking thermostat will not open and will cause the car to overheat. This can lead to bigger issues if the vehicle runs too hot for too long. Replacing the thermostat, when changing out the coolant, will help to ensure the car runs cool.

Step 1

Open the hood to access the coolant system. Place a drain pan under the radiator to catch the old coolant.

Step 2

Unbolt the coolant temperature sensor at the bottom of the radiator with a socket wrench. The coolant will drain once the sensor is removed. Bolt the sensor back onto the radiator once the radiator has drained.

Step 3

Unscrew the hose clamps on the upper radiator hose with a flat head screwdriver. Take the hose off the radiator and the thermostat housing.

Step 4

Remove the three bolts around the thermostat housing with the socket wrench. Remove the top half of the housing by hand.

Step 5

Scrape the old gasket material off both ends of the housing surface. Ensure all the black gasket material is removed to prevent leaking in the future.

Step 6

Pull the old thermostat out of the housing by hand. Replace it with a new thermostat. Ensure the spring side of the thermostat goes in first.

Step 7

Place a new gasket around the surface of the bottom portion of the housing. Place the top half over the bottom half.

Step 8

Tighten the three bolts to secure the thermostat housing with the socket wrench. Slide the radiator hose onto the thermostat housing and the radiator piping.

Step 9

Tighten the hose clamps over both ends with a flat head screwdriver. Ensure the hose is on tight by tugging on it to double-check.

Step 10

Twist the radiator cap counterclockwise and remove it. Pour a gallon of pre-mixed coolant into the radiator.

Step 11

Start the car to allow it to warm up. Do not put the radiator cap onto the radiator.

Step 12

Pour in coolant once the level starts dropping. When the thermostat opens, coolant will be released into the engine. Keep pouring until no more coolant will go into the radiator.

Step 13

Tighten the radiator cap back onto the radiator. Check for any leaks.

Close the hood. Turn off the car.

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