Erratic and Incorrect Engine Temperature Reading (Bleed Air From Cooling System

Some owners may comment about low coolant temperature gauge readings and when performing diagnosis, the technician may notice coolant temperature readings below the actual coolant temperature.

There may be a small pocket of air trapped in the coolant temperature sensor fitting on the radiator inlet pipe. This air pocket insulates the coolant temperature sensor from contact with the coolant flow causing low temperature gauge readings.

REMOVE THE TRAPPED AIR WITH THE FOLLOWING PROCEDURE:

Caution: With a pressurized cooling system, the coolant temperature in the radiator can be considerably higher than the boiling point of the solution at atmospheric pressure. Removal of the surge tank cap, while the cooling system is hot and under high pressure, causes the solution to boil instantaneously with explosive force. This will cause the solution to spew out over the engine, the fenders, and the person removing the cap. Serious bodily injury may result.

1. With the engine off and at ambient temperature, slowly remove the surge tank cap to relieve pressure from the cooling system.
2. Locate the Coolant Temperature Sensor on the Radiator Inlet Pipe.




Notice: DO NOT APPLY TORQUE DIRECTLY TO THE RADIATOR INLET PIPE! Always use a back up wrench on the coolant temperature sensor fitting to prevent damage to the Radiator Inlet Pipe.

3. Observe the gap between the bottom of the hex on the coolant temperature sensor and the top of the hex on the fitting brazed to the radiator inlet pipe. It may be helpful at this point to mark the coolant temperature sensor thread with a reference mark 5 mm (0.196 in) down from the bottom of the hex on the sensor.



4. Slowly loosen the sensor (do not fully remove it) until coolant begins to weep out of the threads. This will allow any trapped air to escape and will ensure that the coolant is in contact with the sensor element.
5. Retighten the Coolant Temperature Sensor until there is a 5 mm (0.196 in) gap between the bottom of the hex on the sensor and the top of the hex on the coolant temperature sensor fitting.



6. Inspect the coolant level in the surge tank, if the coolant is low, add additional coolant to bring the level up to the "Full Cold" mark on the surge tank. Install the surge tank cap.
7. Start the vehicle and inspect the Coolant Temperature Sensor for leaks and correct temperature gauge readings.

For vehicles repaired under warranty, use: