Lesson 4/Learning Event 3
The temperature gage is a very important indicator in automotive equipment. The most common
use is to indicate engine, transmission, and differential oil temperatures and engine coolant
The instrument panel gage may be thermostatic or magnetic. The sending unit that is used with
each type gage varies as follows:
- Thermostatic. The sending unit used with this gage usually contains two bimetallic
strips, each of which has a contact point. One bimetallic strip is heated
electrically; the other bends to increase the tension of the contact points. The
different positions of the bimetallic strip will create gage readings in the same
manner as the different float arm positions of the tank sender.
- Magnetic. The sending unit used with this gage contains a device called a
thermistor. A thermistor is an electronic device whose resistance decreases
proportionally as its temperature increases. This type of sending unit also can be
used with a thermostatic gage if a voltage-limiting device is used.
The temperature warning light is used on many vehicles in place
of a gage. The indicator light, although not as detailed as a gage, is valuable because of its high
visibility in the event of an overheat condition. Because an engine can become damaged
permanently or destroyed by operating for short periods while overheated, warning lights often are
used as a backup for temperature gages to attract instant attention to a malfunction.