M11 Series – Service Manual – 008-013   Coolant Thermostat

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  Complete this test with the engine coolant temperature below 50°C [120°F]. Hot steam can cause serious personal injury.

Remove the radiator hose from the thermostat housing.

Install a thermocouple or temperature gauge, which is known to be accurate, in the water header plate or engine side of the thermostat housing.

Install a hose of the same size on the thermostat housing outlet 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.

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 or thermostat seal is leaking and must be replaced. Refer to Procedure 008-016 to replace the thermostat seal.

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

Start the engine and monitor the water temperature gauge 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 coolant system pressure cap. Heated coolant spray or steam can cause personal injury.

Remove the pressure cap when the engine is cool.

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 coolant hose from the thermostat housing.

Loosen the coolant bypass hose clamps.

NOTE: Some models could have a converter cooler disc located in the bypass hose. Refer to Procedure 008-065.

Remove the four thermostat housing mounting capscrews and the thermostat housing.

Remove the thermostat from the housing.

Inspect the thermostat seal for cracks, corrosion, or other damage.

If the seal is damaged, it must be replaced. Refer to Procedure 008-016.

Inspect the thermostat for damage.

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

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

Heat the water, and check the thermostat as follows:

The nominal operating temperature is stamped on the thermostat.

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

The fully open distance between the thermostat flange and housing is 11 mm [0.435 in].

If the thermostat operates properly and more than 100 cc [3.3 fl. oz] leakage is detected during in-chassis test, replace the thermostat seal. Refer to Procedure 008-016.

Install the thermostat in the housing.

Install a new o-ring seal in the groove on the thermostat housing mounting surface.

Install the hose on the thermostat housing bypass outlet.

Install the thermostat housing and four mounting capscrews.

Tighten the mounting capscrews.

NOTE: If a torque converter cooler disc is used in the coolant bypass hose, refer to Procedure 008-065.

Install the upper coolant hose to the thermostat housing outlet. Tighten the hose clamp.

Refer to the OEM service manual for the correct torque value.

Tighten the coolant bypass hose clamps.

Close the cooling system draincock, and install the lower coolant hose.

Tighten the hose clamp.

Refer to the OEM service manual for the correct torque value.

The correct concentration of coolant additives must be used in the cooling system. Refer to Section V in the Operating and Maintenance Manual, M11 Plus Series Engines, Bulletin 3666143.

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

Operate the engine until it reaches 80°C [180°F], and check for coolant leaks.