CASE AS-TRANSMISSION 4175204 - Caterpillar

Theory of Operation
The low coolant sensor is an electronic device that measures capacitance. The capacitance that is measured from the probe that is surrounded by coolant, and the capacitance that is measured from the probe that is surrounded by air is different. The output characteristics of the sensors are shown in 1.
Table 1
Coolant Level Sensor Gp     Dry Output     Submerged Output    
107-0174     0 VDC     Open Circuit    
165-6634     5 VDC     0 VDC    
204-2518     5 VDC     0 VDC    
239-9957     5 VDC     0 VDC    Critical Surfaces of the Sensor
Illustration 1 g01228306
(1) Tie wrap (2) Body (3) ProbeThe critical surfaces of the sensor are body (2) and probe (3). It is essential that the sensor body surface, and the surface must not electrically connect to each other. The probe is encased in a clear plastic sheath. The sheath is a nonconductive material that insulates the probe from surrounding conditions (coolant, steam, or air). This sheath extends into the body of the sensor and the sheath ensures that the probe is isolated from the sensor body.Note: Coolant is conductive. When coolant is in contact with the threads of the sensor body, the coolant becomes an extension of the sensor body. The sensor electronics will then measure the capacitance between the probe and the sensor body.
Important - if the plastic sheath develops a leak for any reason, the coolant will short the probe tip to the body, rendering the sensor non-functional. Make sure that the plastic sheath is intact.
Installation Notes
Special Care During Installation
Often during installation, sensors are damaged. When you are installing the sensor, you must be careful to ensure that the sensor probe is not cut by the threads of the mounting boss. The sensor probe can also be scratched by the threads of the mounting boss.Installation on Generators with a Lifting Eye on the Radiator
If the sensor is to be installed into a radiator in a location directly behind a lifting eye, you must cut the tie wrap from the adapter harness. Next, disconnect the adapter harness and remove the adapter harness before installing the sensor. After the sensor is installed and the adapter harness reconnected, install another tie wrap.Service Note
Engine Cleaning or Washing
Illustration 2 g01597677
(2) Sensor bodyDirect pressurized spray may penetrate the seals of the sensor. Also, direct pressurized spray will damage the sensor. Damage to the sensor can affect the output of the sensor. When the equipment must be pressure washed, do not spray the sensor directly with pressures that exceed 34 kPa (5 psi).