How to Test a Coolant Sending Unit on a Small Chevy

Small block Chevrolet engine cooling systems use a sending unit to control when the coolant flows from the radiator to the engine. Once the engine reaches a specified temperature, the sending unit opens and allows the coolant to enter the engine. When the engine falls below that temperature, the unit closes, thereby allowing the engine to warm. Defective sending units usually fail to open, but they can also fail to close. Testing the sending unit can be quickly performed by immersing the unit in water and raising the temperature of the water while monitoring with a thermometer.

Things You'll Need

• Engine specifications manual
• Saucepan
• Water
• Stove
• Thermometer

Instructions

1. Consult the engine specifications manual to determine the temperature at which the sending unit should open. The majority of sending units used by Chevrolet small block engines are designed to open at 180 degrees Fahrenheit. However, a few Chevy sending units open at 170 or as high as 195 degrees. The type of sending unit depends on the type of engine so consult the specifications manual.

2. Fill a saucepan with cold water and place the pan over a stove burner.

3. Place the sending unit in the pan.

4. Insert the tip of a thermometer into the pan.

5. Turn the oven’s burner on to medium heat and monitor the thermometer and the sending unit.

6. Note the temperature of the water at which the sending unit opens. If the sending unit does not open at the proper temperature, the sending unit is defective and must be replaced.

7. Allow the water to cool, while monitoring the sending unit, if the sending unit opened at the proper temperature. If the sending unit fails to close after the water cools, the sending unit is defective and must be replaced.

References

• "Popular Mechanics Complete Car Care Manual;" Popular Mechanics; 2005
• "Motor's Auto Repair Manual;" Ralph Ritchen; 1968