Coolant Thermostat, Checking

WARNING: This page is about a different car, the 2024 Audi RS 3. However, it is still accessible from the selected car via links, so may be relevant.

Special tools and workshop equipment required

Temperature Gauge (Infrared) :VAS 6886

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Test Requirement

The engine is cold.
Vehicle at room temperature.

Start of test:

-- Start the engine.

-- Adjust the A/C system on the A/C controls to "A/C off" mode.

CAUTION:

There is a risk of injury if the radiator fan turns on by itself.

- When working near the radiator, maintain a distance from the fan.

CAUTION:

Risk of being burned due to hot components in the engine/motor compartment. Possible to burn hands and other parts of the body.

- Keep a distance to hot components when working in the engine/motor compartment.

- Wear personal safety equipment.

-- Using the Valve Spring Adapter :VAS 6886 determine the surface temperature of the coolant hoses at the following locations:

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-- Cylinder head output

-- Radiator input

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-- Radiator output

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-- The measured values must be identical.

-- Let the engine run, at the same time measure the surface temperature of the coolant hoses at the locations named above at regular intervals.

-- The temperature increase must keep to the curve shown in the diagram.

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A -

Surface temperature of the coolant hoses on the cylinder head

B -

Surface temperature of the coolant hoses on the radiator input

C -

Surface temperature of the coolant hoses on the radiator output

-- After about 35 to 40 minutes the surface temperature of all three coolant hoses must be in the same temperature range.

Coolant thermostat open
Radiator fan turns on

-- If this is the case the coolant thermostat is OK.

-- If after 35 to 40 minutes the surface temperature on the output of the radiator varies greatly from the surface temperature on the cylinder head output and on the radiator input, this is a sign that the coolant thermostat is faulty (coolant thermostat is stuck closed).

-- If before starting the measurement, the surface temperature on the output of the radiator rises in proportion to the cylinder head output and radiator input, if this is an sign of a faulty coolant thermostat (the case is stuck open).

If the specified values are not OK replace the coolant distribution housing with the coolant thermostat. Refer to COOLANT DISTRIBUTION HOUSING, REMOVING AND INSTALLING .

TIP:

-- The test named above can also be performed at an increased idle speed. This correspondingly shortens the time requirement.