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.

NOTE: The N14 CELECT™ and CELECT™ Plus engines have one engine coolant thermostat and one aftercooler thermostat. The N14 STC engines have two engine thermostats and no aftercooler thermostat. The illustration reflects the N14 CELECT™ engine, but is representative of all the engines.

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

Remove the upper radiator hose from the thermostat housing.

Install a hose of the same size onto the thermostat housing outlet long enough to reach a remote dry container used to collect coolant.

Install and tighten a hose clamp onto the housing outlet.

Place the end of the hose into a dry container.

Operate the engine at rated rpm for one (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 the thermostat seal is leaking.

Remove the thermostat. Refer to Procedure 008-014 in Section 8.

Inspect the thermostat seal. Refer to Procedure 008-016 in Section 8.

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 11.05 mm [0.435 in] within 12°C [22°F] above nominal temperature.

Replace the thermostat if it does not operate as described.