Truck Dash Gauges and What They Mean

As trucks get more sophisticated, the monitoring of these complex machines becomes more important. It is our belief that within the next decade, dash gauages will be replaced with microcontroller displays which can evaluate the conditions and provide both visual and audible alarm when conditions warrant. For now though, you had better understand all these gauges.
We aren't going to treat you like a fool and explain what the speedometer, temperature gauge, and oil gauges do. But we will explain what range most readings should be within, and we will explain those gauages which aren't normally found on cars.

The following gauge readings and purposes are typical. For your particular truck, consult the manufacturers manual for exact parameters:

  • Oil Pressure - hot idle should be 10-20 PSI, normal operating range 30-70 PSI
  • Water Temp - normal is 165 - 185 degrees, although the temp may be higher if
    you are pulling a heavy load upgrade or you are operating in extremely hot weather.
  • Voltmeter - they usually have three colored bands, left-hand red indicates under-charging,
    middle green indicates normal charging, right-hand red indicates over-charging.
  • Pyrometer - indicates the exhaust temperature, this very responsive gauge indicates how
    hard the engine is working, stay within the indicated safe range.
  • Transmission temp - oil temp range is usually 180-250 degrees, large changes are abnormal
  • Front Driver Axle temp - oil temp range is usually 160-250 degrees, large changes are abnormal
  • Rear Driver Axle temp - oil temp range is usually 160-250 degrees, large changes are abormal
  • Fuel Filter Gauge - measures the pressure drop across the fuel filter, two bands, white band OK, and red band means that the filter needs replacement.
  • Air pressure gauge - measures your trucks reservoir air pressure PSI, you may have two or
    more gauges, one for each reservoir, normal readings 100-120 PSI. Don't drive the vehicle until the pressure is above 90 PSI. Pull over if the air pressure drops below 90 PSI., because the air compressor governor is required to keep the air pressure above 90 PSI. If the pressure falls below 90 PSI, you have a large air leak, or the compressor is not working properly. No air ... no brakes!
  • Engine Air Filter Gauge - indicates pressure drop across the engine air filter. Most truck air compressors also get their supply from this filter. Red area reading indicates a clogged air filter, which can also limit your air compressor output.

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