ISC, ISCe, QSC8.3, ISL, ISLe3, ISLe4 and QSL9 Engines – 008-013   Coolant Thermostat

The thermostat controls the coolant temperature. When the coolant temperature is below operating temperature, coolant is bypassed to the inlet of the water pump. When the coolant temperature reaches the operating range, the thermostat opens, seals off the bypass, and forces coolant to flow to the radiator or the keel cooler on QSL9 marine engines. The thermostat begins opening at 82°C [180°F].

CAUTION  Never operate the engine without a thermostat. Without a thermostat, the path of least resistance for the coolant is through the bypass to the pump inlet. This will cause the engine to overheat.

An incorrect or malfunctioning thermostat can cause the engine to run too hot or too cold.

NOTE: The leak test portion of this procedure does not apply to QSL9 keel cooled marine engines. To test QSL9 keel cooled engines. Refer to Procedure 008-014 in Section 8.

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.

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.

CAUTION  On marine engines, use caution when draining coolant that coolant is not spilled or drained into the bilge area. Do not pump the coolant overboard. If the coolant is not reused, it must be discarded in accordance with local environmental regulations.

Drain the coolant. Refer to Procedure 008-018 in Section 8.

Remove the radiator hose from the water outlet connection.

Use an electronic service tool to monitor the coolant temperature, or install a thermocouple or temperature gauge, which is known to be accurate, in the cylinder block on the engine side of the thermostat.

Install a hose of the same size on the water outlet connection long enough to reach a remote, dry container used to collect coolant.

Install and tighten a hose clamp on the housing outlet.

Place the other end of the hose in a dry container.

CAUTION  Always vent the engine and aftercooler during filling to remove air from the coolant system, or overheating will result.

Fill the cooling system. Refer to Procedure 008-018 in Section 8.

NOTE: The engine coolant temperature must be below the thermostat opening temperature to perform this test.

Operate the engine at rated speed for 1 minute.

Shut the engine off 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 is leaking and must be replaced.

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

Start the engine and monitor the coolant temperature with INSITE™ electronic service tool or a gauge. Keep the engine speed below 1500 rpm during the test.

Thermostat Initial Opening Temperature

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  Batteries can emit explosive gases. To reduce the possibility of personal injury, always ventilate the compartment before servicing the batteries. To reduce the possibility of arcing, remove the negative (-) battery cable first and attach the negative (-) battery cable last.

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.

• Disconnect the batteries. Refer to Procedure 013-009 in Section 13.
• Drain the coolant. Refer to Procedure 008-018 in Section 8.
• Remove the radiator hose from the water outlet connection.

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.

CAUTION  Use caution when draining coolant that coolant is not spilled or drained into the bilge area. Do not pump the coolant overboard. If the coolant is not reused, it must be discarded in accordance with local environmental regulations.

• Drain the engine coolant. Refer to Procedure 008-018 in Section 8.
• On QSC8.3 and QSL9 engines with heat exchangers, remove the coolant hose from the water outlet connection.

• On QSL9 engines with keel cooling, remove the coolant hose from the inlet side of the keel cooler thermostat housing.

Remove the water outlet connection capscrews and water outlet connection.

Remove the thermostat.

On marine engines with heat exchangers, remove the water outlet connection capscrews and the water outlet connection from the top of the cylinder head.

On QSL9 engines with keel cooling, remove the water inlet connection capscrews and the water inlet connection from the keel cooled thermostat housing.

Clean all of the mating surfaces.

NOTE: Do not let any debris fall into the thermostat cavity when cleaning the surfaces.

Inspect the thermostat for damage.

Inspect the thermostat gasket for damage. If the gasket is damaged, it must be replaced.

NOTE: Do not allow the thermostat or thermometer to touch the container.

Heat the water and check the thermostat as follows:

Suspend the thermostat and a 100°C [212°F] thermometer in a container of water.

The nominal operating temperature is stamped on the thermostat. The thermostat must meet the following criteria:

• The thermostat must begin to open within 1°C or 2°F of this nominal temperature.
• The thermostat must be fully open within 12°C or 22°F of this nominal temperature.

The fully open distance between the thermostat flange and housing is 9.4 mm [0.370 in].

On QSC8.3 and QSL9 engines with heat exchangers, install the thermostat into the water outlet connection. Make sure that the top and bottom o-rings are in place.

Install the water outlet connection and mounting capscrews.

On QSL9 engines with keel cooling, install the thermostat into the water inlet connection of the keel cooled thermostat housing.

Install the water outlet connection.

WARNING  Batteries can emit explosive gases. To reduce the possibility of personal injury, always ventilate the compartment before servicing the batteries. To reduce the possibility of arcing, remove the negative (-) battery cable first and attach the negative (-) battery cable last.

CAUTION  Always vent the engine and aftercooler during filling to remove air from the coolant system, or overheating will result.

• Fill the cooling system. Refer to Procedure 008-018 in Section 8.
• Connect the batteries. Refer to Procedure 013-009 in Section 13.
• Operate the engine and check for leaks.