Centinel System – Repair Manual – 008-013   Coolant Thermostat

Signature, ISX, and QSX engines use two engine coolant thermostats.

The engine thermostat and thermostat seal must operate properly in order for the engine to operate in the most efficient heat range. Overheating or overcooling will shorten engine life.

Refer to Procedure 008-016 to inspect the thermostat seal.

WARNING  Do not remove the pressure cap from a hot engine. Wait until the coolant temperature is below 50°C [120°F] before removing the pressure cap. Heated coolant spray or steam can cause personal injury.

WARNING  Coolant is toxic. Keep away from children and pets. If not reused, dispose of in accordance with local environmental regulations.

Drain the coolant to a level below the vent line in the thermostat housing.

Disconnect and plug the vent line hose. Refer to Procedure 008-017.

Remove the radiator hose from the radiator top tank.

The radiator hose must be at the point of overflowing before the engine is run. Small amounts of leakage will not be detected if the hose is not pre-filled.

Fill the radiator hose with coolant until coolant is just about ready to flow out of the hose.

Place a dry container under the end of the hose.

Operate the engine at rated rpm for three minutes.

Shut off the engine and measure the amount of coolant collected in the container.

The amount of coolant collected must not be more than 100 cc [3.3 fl oz].

If more than 100 cc ]3.3 fl oz] of coolant is collected, the thermostat or thermostat seal is leaking.

Remove the thermostats and test their operation as described in the Out-of-Chassis Opening Temperature Test in this procedure.

Refer to Procedure 008-016 for thermostat seal inspection.

NOTE: An electronic service tool can also be used to monitor the thermostat opening temperature without removing the radiator hose.

Remove the coolant temperature sensor and install a thermocouple or temperature gauge, which is known to be accurate, on the engine side of the thermostat housing.

Complete the following test in-chassis to test the thermostat opening temperature.

Start the engine and monitor the water temperature and the container.

Shut off the engine when the coolant starts to flow.

If coolant does not start flowing into the container during the initial opening temperature range, the thermostat must be replaced.

WARNING  Do not remove the pressure cap from a hot engine. Wait until the coolant temperature is below 50°C [120°F] before removing the pressure cap. Heated coolant spray or steam can cause personal injury.

WARNING  Coolant is toxic. If not reused, dispose of in accordance with local environmental regulations.

Drain the cooling system. Refer to Procedure 008-018.

Remove the upper radiator hose from the thermostat housing cover.

Disconnect vent line.

Disconnect the coolant sensor connector.

Remove the four capscrews that attach the thermostat housing cover to the thermostat housing.

Remove the thermostat housing cover and gasket from the thermostat housing. Discard the gasket.

Remove the thermostats from the thermostat housing cover.

Inspect the thermostat for damage.

Suspend the thermostat and a 100°C [212°F] thermometer into a container of water. Do not allow the thermostat or the thermometer to touch the sides of the container.

Heat the water.

Record the temperatures at which the thermostat begins to open and when it is fully open.

The nominal operating temperature is stamped on the thermostat.

• The thermostat must begin to open within 1°C [2°F] of nominal temperature.
• The thermostat must be fully open to at least 11 mm [0.435 in] within 12°C [22°F] above nominal temperature.

Replace the thermostat if it does not operate as described.

Install the two thermostats into the thermostat housing cover by pushing on the outer rims.

Install the thermostat housing cover, gasket, and four capscrews on the cylinder head.

Tighten the capscrews to the values shown.

Connect the vent line. Refer to the OEM instructions.

Connect the coolant sensor connector.

Industrial engines use a thermostat housing cover with either a cover plate or a water connection.

If removed, tighten the capscrews to the following specification.

Install the upper radiator hose. Tighten the hose clamp.

Fill the cooling system. Refer to Procedure 008-018.

Operate the engine until the coolant temperature reaches 70°C [160°F]. Check for leaks.