Oil Temperature Gauge: Description and Operation
An oil temperature gauge (1) is standard equipment on all SRT-10 models. This electronic, analog gauge is located in the lower end of the left A-pillar trim molding below the grab handle (2), in clear view of the vehicle operator. The gauge dial face is visible through a clear plastic lens, which is secured to the gauge housing with a silver anodized trim ring. The remainder of the gauge, including the mounting provisions and the electrical connections, are concealed behind the left A-pillar trim molding.
The molded plastic housing at the rear of the gauge protects the electronic circuitry of the gauge and has two mounting studs, which are secured by nuts to a molded plastic mounting bracket screwed to the back of the A-pillar trim molding. A short pigtail wire with a connector extends from the back of the gauge housing and connects the gauge to the vehicle electrical system through a take out and connector of the instrument panel wire harness.
The oil temperature gauge consists of a movable gauge needle or pointer with a 270 degree sweep that is controlled by the electronic gauge circuitry. The gauge overlay reads left-to-right from "60" to "150" with "° C" indicated directly below the low (left) end of the scale in markets where a metric instrument cluster is specified, or from "140" to "300" with "° F" indicated directly below the left end of the scale for all other markets. The text "OIL TEMP" is imprinted on the center of the gauge overlay below the hub of the gauge needle, while the text "SRT" is imprinted above the hub of the gauge needle. The gauge graphics are black against a silver field except for a single red zone at the high (right) end of the gauge scale and are clearly visible in daylight.
General illumination lighting for the gauge is provided by a Light Emitting Diode (LED) that is soldered onto the gauge circuit board. The gauge overlay is a laminated plastic unit. The dark, visible, outer surface of the overlay is marked with the gauge dial face and graduations, but this layer is also translucent. The underlying layer of the overlay is opaque and allows light from the LED on the circuit board behind it to be visible through the outer layer of the overlay only through predetermined stencil-like cutouts. When illuminated from behind by the panel lamps dimmer controlled gauge lighting with the exterior lamps turned On, the black graphics appear blue-green and the red graphics still appear red. The gauge needle has internal optical illumination.
The oil temperature gauge cannot be repaired or adjusted and, if damaged or faulty, it must be replaced. The gauge illumination LED unit is not available for service replacement and, if damaged or faulty, the entire gauge must be replaced.
The oil temperature gauge gives an indication to the vehicle operator of the engine oil temperature. This gauge is controlled by its own internal electronic circuit board based upon a hard wired input received by the gauge from an oil temperature sensor (4) installed in a tapped hole that penetrates an oil passage on the right side of the engine block (2) just behind the oil pressure sensor (3).
The oil temperature sensor is a Negative Temperature Coefficient (NTC) thermistor that changes its internal resistance with changes in temperature. The sensor has two terminals. One terminal receives a hard wired ground path through a take out and connector of the engine wire harness (1), and the second terminal provides a variable output to the gauge through the same take out and connector. As the oil temperature increases the resistance of the sensor decreases, and as the oil temperature decreases the resistance of the sensor increases.
The oil temperature gauge is an air core magnetic unit. The gauge pigtail wire and connector provides the gauge electronic circuit board with a hard wired ground path, battery current through a fused ignition switch output (run-start) circuit, a Pulse Width Modulated (PWM) panel lamps dimmer input from the instrument cluster for general illumination, and the input from the oil temperature sensor. This gauge is only operational when the ignition switch is in the On or Start positions. The gauge electronic circuit board reads the input from the oil temperature sensor, then provides linear positioning of the gauge needle on the gauge scale based upon that input. The gauge electronics will move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position.
The oil temperature gauge and the oil temperature sensor may be diagnosed using conventional diagnostic tools and methods.