ISBe/ISB Series Engines – 008-013   Coolant Thermostat

The thermostat controls the engine coolant temperature. When the coolant temperature is below the operating range, engine coolant is bypassed back to the inlet of the water pump. When the engine coolant temperature reaches the operating range, the thermostat opens, sealing off the bypass, forcing engine coolant to flow to the radiator or heat exchanger.

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

CAUTION  A missing check ball can cause the engine to run cold, resulting in engine damage.

The thermostat contains two check balls to vent air past the thermostat when it is closed. This is needed for the cooling system to fill.

NOTE: Some off-highway applications use a thermostat with one check ball. When servicing a thermostat always be sure to replace with the same part number. Though an incorrect thermostat will physically fit, it will lead to improper engine operation.

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.

Disconnect the batteries.

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

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.

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 coolant below the level of the thermostat. Refer to Procedure 008-018.

WARNING  Complete this test with the engine coolant temperature below 50°C [122°F]. Hot steam can cause serious personal injury.

Loosen radiator hose clamp.

Remove the radiator hose from the water outlet connection. Refer to Procedure 008-045.

Marine applications, remove the heat exchanger hose from the water outlet connection and plug the heat exchanger engine coolant inlet connection. Refer to Procedure 008-053.

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 water header plate on the engine side of the water outlet connection.

Marine applications, use the service tool to monitor engine temperature.

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 water outlet connection.

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

Operate the engine at rated rpm for 1 minute.

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 is leaking and must be replaced.

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

Start the engine and monitor the water temperature with an electronic service tool or a gauge.

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.

Remove the water outlet connection capscrews.

Remove the water outlet connection.

Remove the thermostat.

CAUTION  Do not let any debris fall into the thermostat cavity when cleaning the gasket surfaces. Damage to the cooling system and engine can occur.

Clean the mating surfaces with a gasket scraper and a clean cloth.

Inspect the thermostat for cracks, tears, damage, missing soft seat.

Remove and discard the gasket.

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

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

Heat the water and check the thermostat as follows:

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

• It must begin to open within 1°C [2°F] of nominal temperature.
• It must be fully open within 12°C [22°F] of nominal temperature.

The nominal operating temperature for Marine application engines must meet the following criteria:

• It must begin to open with 1°C [2°F] of nominal temperature.
• It must be fully open within 14°C [15°F] of nominal temperature.

NOTE: The fully open distance between the thermostat flange and housing is 14.3 mm [0.563 in] minimum.

CAUTION  Always use the correct thermostat and do not operate the engine without a thermostat installed. The engine can overheat if operated without a thermostat because the path of least resistance for the coolant is through the bypass to the pump inlet. An incorrect thermostat can cause the engine to overheat or run too cold.

Install the thermostat into the thermostat housing.

NOTE: Make sure a new thermostat seal is installed on the outer lip of the thermostat flange every time the thermostat is reinstalled.

Install the water outlet connection and mounting capscrews.

Tighten the capscrews.

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

On marine applications, install the heat exchanger coolant hose. Refer to Procedure 008-053.

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

NOTE: On engines with EGR, the pipe plug in the EGR coolant line must be removed during filling.

NOTE: Marine applications, vent air from the vent on top of the engine coolant 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.

Connect the batteries.

Operate the engine and check for leaks.