Digital Thermometers for Workshops and Vehicle Diagnostics

Frequently Asked Questions About Digital Thermometers for Workshops and Vehicle Diagnostics

Temperature readings are only meaningful if the measurement location, sensor type, operating conditions, and measurement method are appropriate for the specific diagnostic task. For example, a surface temperature cannot simply be compared to a fluid temperature or an electronically measured sensor value. Here, we answer frequently asked questions about the selection and use of Leitenberger digital thermometers.

• What digital thermometers does Leitenberger currently offer?

  This subcategory currently includes two devices:

  Device Main Application Measurement Range
  AR 203_LR Universal temperature measurement with combination probe -65 to +500 °C
  AR 204_LR: Two-channel and differential temperature measurement; thermometer range: -200 to +1350 °C; included probes: -65 to +500 °C
   

  The AR 203 has one measurement channel and a replaceable combination probe. The AR 204 has two channels for Type K thermocouples.

• What is a digital thermometer used for in an auto repair shop?

  A digital thermometer can be used, for example, to monitor temperatures on components, in liquids, or in airflows, and to compare different measurement points with one another.
  
  Possible applications include engines, cooling systems, air conditioning systems, transmissions, hydraulic systems, and other components subject to thermal stress.
  
  The specific measurement method must be appropriate for the diagnostic task at hand.

• What is AR 203_LR?

  The AR 203_LR is a digital second-type thermometer with a 3½-digit LCD display and a replaceable combination probe.

  The measurement range is -65 to +500 °C, with a resolution of 1 °C. The measurement cable is 1 m long. The device is powered by a 9-V block battery and comes in a plastic case.

• What can be measured with the AR 203_LR?

  Leitenberger specifically mentions rapid temperature measurements of:

  surfaces, liquids, air, and gases.

  A combination probe is used for this purpose.

• Can the AR 203's sensor be replaced?

  Yes.

  The combination sensor is connected to the handheld unit via a plug and can be disconnected or replaced.

  The ET 522 combination sensor is available as a replacement part.

• How long is the AR 203's test lead?

  The measurement cable of the AR 203_LR is 1.00 m long. This allows the handheld device to be held at a distance from the actual measurement point during a measurement.

• What is the resolution of the AR 203?

  The temperature display has a resolution of 1 °C.

• What is AR 204_LR?

  The AR 204_LR is a precision digital thermometer with two measurement channels.

  It can simultaneously read two Type K thermocouples and switch between the two individual channels or perform a direct differential measurement. Two Type K thermocouple surface probes are included with the unit.

• What is a differential temperature measurement?

  In a differential temperature measurement, two temperatures are recorded simultaneously and their difference is determined.
  
  This allows, for example, an immediate comparison of how much the temperature varies between two measurement points.
  
  The AR 204_LR can determine this difference directly from the two connected sensors.

• Why is measuring temperature differences helpful in vehicle diagnostics?

  Often, it is not just the absolute temperature of a single component that is of interest, but the difference between two points.
  
  For example, this allows for the comparison of inlet and outlet temperatures or of two comparable components under the same operating conditions.
  
  A noticeable difference can then serve as an indication for further diagnostic work. However, it does not in itself prove the presence of a specific defect.

• Is AR 204 suitable for air conditioning systems?

  Yes.

  Leitenberger specifically cites professional temperature differential measurement in air conditioning systems as a typical application of the AR 204_LR. The device is therefore also listed in the Test and Diagnostic Equipment for Automotive Air Conditioning Systems category.

• Why are two temperature sensors useful when diagnosing an air conditioning system?

  With two probes, two measurement points can be recorded simultaneously.

  Compared to two individual measurements taken one after the other, this has the advantage that both values are recorded under nearly identical operating and environmental conditions.

  For such tasks, the AR 204 can therefore complement the test and diagnostic equipment for automotive air conditioning systems.

• Which sensors are included with the AR 204?

  The package includes two Type K thermocouple surface probes.

  The measurement range of these included probes is -65 to +500 °C.

• What does “Type K thermocouple” mean?

  Type K refers to a standardized thermocouple type made from a specific combination of materials.
  
  AR 204_LR is designed for Type K thermocouples.
  
  Therefore, a distinction must be made between the measurement range of the handheld device and the permissible measurement range of the respective connected probe.

• What is the measurement range of the AR 204?

  The handheld unit itself is specified for a range of -200 to +1350 °C.

  The two surface probes included as standard, on the other hand, have a range of -65 to +500 °C.

• Can I measure temperatures up to +1,350 °C using the included probes?

  No.

  That is an important distinction.

  The measuring device can measure Type K signals up to +1350 °C. However, the included surface probes are only rated up to +500 °C.

  For higher temperatures, a suitable and compatible Type K probe would therefore be required.

• What is the resolution of the AR 204?

  In the range from -99.9 to +99.9 °C, the resolution is 0.1 °C.

  Outside this range, up to the specified measurement limits, the resolution is 1 °C.

• How fast does the AR 204 measure?

  The specified measurement interval is 100 ms.

  This allows the device to update the measurement value quickly and makes it suitable for monitoring temperature changes.

• Can the AR 204 be used with just one sensor?

  Yes.
  
  Leitenberger explicitly points out that the device can also be used with just one sensor connected.

• Do I always have to use both measurement channels for AR 204?

  No.
  
  If only a single temperature is needed, a single channel can be used.
  
  The second channel and the difference function are particularly useful when two measurement points need to be compared simultaneously.

• What temperature units can the AR 204 display?

  The device can be switched between:

  °C, °F, and K.

• Does the AR 204 have a display backlight?

  Yes.
  
  The AR 204 features a four-digit backlit LCD display. The digit height is 16 mm.

• What is the difference between AR 203 and AR 204?

  The AR 203 is the simpler, universal handheld thermometer with a combination probe.

  The AR 204, on the other hand, offers two measurement channels and differential temperature measurement.

  In short:

  AR 203: Quickly measure a single temperature.
  AR 204: Measure two temperatures simultaneously and compare them.

• Which device is best suited for simple temperature control?

  If you primarily need individual temperature readings from surfaces, liquids, air, or gases, the AR 203_LR is the simpler solution.
  
  The combination probe is suitable for a variety of measurement tasks.

• Which device is suitable for temperature comparisons?

  When two measurement points need to be evaluated simultaneously or a temperature difference needs to be assessed, the AR 204_LR offers a decisive advantage.
  
  The two measurement channels and the integrated difference function are designed precisely for such applications.

• Can a digital thermometer be used to check the coolant temperature?

  In general, suitable sensors can be used for measuring liquid temperature.

  AR 203 is specifically described for use with liquids as well.

  However, when working on the cooling system, temperature, system pressure, and the hazard posed by hot coolant must be taken into account. A pressurized, hot cooling system must not be opened solely for the purpose of inserting a temperature sensor.

  For additional diagnostic options, see Test Equipment for Cooling Systems.

• Can this be used to check the coolant temperature displayed by the engine control unit?

  An independent temperature measurement can generally be used as additional comparative data.

  However, it is important to consider where the measurement is taken.

  For example, a surface temperature reading taken on the hose or housing is not automatically the same as the temperature recorded by a sensor immersed in the coolant.

  Direct measurements should therefore only be compared if the measurement location and method are appropriately taken into account.

• Can you use it to measure the engine oil temperature?

  In principle, oil temperature can also be measured using a probe designed for liquid measurement.

  AR 203 is suitable for measuring liquids and has a range up to +500 °C.

  However, it is crucial to have a safe and technically suitable access point for measurement. The sensor must not simply be inserted into a running engine at an unsuitable location.

  For further work on the oil circuit, Engine Lubrication & Oil Service are available.

• Can a surface sensor replace the actual oil or coolant temperature?

  Not necessarily.
  
  A surface temperature measured on the outside of a housing or hose may differ from the actual temperature of the medium inside.
  
  A surface measurement is therefore particularly useful if the manufacturer’s specifications also call for this measurement point or method, or if comparative measurements are being performed.

• Can the temperature of the coolant hoses be compared?

  Yes, with the right surface sensors, you can compare temperatures at different locations.
  
  Such measurements can be used, for example, as supplementary diagnostic information.
  
  However, a temperature difference alone does not automatically prove that a thermostat, radiator, or other component is defective.

• Can a digital thermometer detect a faulty thermostat?

  Temperature measurements can provide information about a cooling system’s opening behavior or temperature response.
  
  However, the diagnosis of a thermostat should be based on the entire temperature curve, the specified setpoints, and, if necessary, additional measurements.
  
  A single surface temperature reading is not sufficient for a reliable diagnosis.

• Can a digital thermometer be used to test a radiator?

  Comparing temperatures across different areas can provide insights into heat transfer and temperature distribution.

  However, the results must be evaluated in conjunction with:

  • Coolant temperature
  • Thermostat function
  • Fan function
  • Coolant flow rate
  • System pressure

  For more testing equipment, see Testing Equipment for Cooling Systems.

• Can you measure temperatures on the air conditioner?

  Yes.

  According to Leitenberger, the AR 204_LR in particular is designed for precise differential temperature measurements on air conditioning systems.

  This allows temperature measurements to complement pressure and leak testing in the area of test and diagnostic equipment for automotive air conditioning systems.

• Does a temperature measurement replace the pressure test for an air conditioning system?

  No.

  Temperature and pressure are different diagnostic parameters.

  A temperature measurement can provide insight into the operation of an air conditioning system, but it does not replace:

  • Pressure measurement
  • Leak test
  • Refrigerant test
  • Manufacturer specifications.

  These procedures complement each other.

• Can a digital thermometer replace an air conditioning service?

  No.

  The thermometer is used to measure or compare temperatures.

  It does not evacuate, recharge, or check an air conditioning system for leaks.

  Special testing and diagnostic tools for automotive air conditioning systems are available for that purpose.

• Is it possible to compare temperature differences on cylinders or exhaust manifolds?

  Temperature differences in comparable components can generally provide additional clues during a diagnosis.

  However, the following conditions must be met:

  • same measurement points
  • same sensor contact
  • same operating conditions
  • permissible sensor temperature

  must be observed.

  A temperature difference alone does not prove a specific cause, such as an ignition, fuel injection, or compression fault.

• Can a temperature measurement detect a compression fault?

  Not directly.

  A mechanical compression fault must be diagnosed using compression pressure testers or, if necessary, an engine pressure loss tester.

  Temperature differences can, at most, provide additional clues about varying combustion conditions.

• Can a thermometer detect a faulty injector?

  Not clear-cut.

  Variations in temperature can have various causes.

  If an injector malfunction is suspected, specific injector and fuel injector testers for gasoline and diesel engines or other fuel diagnostics should be used.

• Can you take noncontact measurements with the AR 203 or AR 204?

  No.

  The two devices currently listed use contact probes.

  The AR 203 uses a combination probe, and the AR 204 uses a Type K thermocouple probe.

• Is a digital thermometer the same as an infrared thermometer?

  No.
  
  An infrared thermometer measures surface temperature without contact, using thermal radiation.
  
  In contrast, the Leitenberger AR 203 and AR 204 devices currently listed in this category operate with connected contact probes.

• Why is the probe contact important in surface measurements?

  When performing a contact measurement, the probe must be thermally coupled to the measurement point in as reproducible a manner as possible.
  
  Variations in contact pressure, contaminated surfaces, or changing measurement positions can affect the measured value.
  
  Therefore, conditions should be kept as identical as possible during comparative measurements.

• Why should measurements always be taken at the same spot?

  Even a distance of just a few centimeters can result in different temperatures on thermally stressed components.

  To ensure reproducible comparisons, the following should therefore remain as consistent as possible:

  • Measurement point
  • Sensor position
  • Operating condition
  • Measurement duration.
• Can the AR 204 quickly display temperature changes?

  The specified measurement interval of 100 ms allows for rapid updating of the measured values.
  
  However, the actual response time of a measurement also depends on the sensor used, the measurement location, and heat transfer.

• Is the measurement interval the same as the sensor's response time?

  No.
  
  The measurement interval describes how often the device processes or updates a measurement value.
  
  How quickly the sensor itself reaches the actual temperature at the measurement point, on the other hand, depends on its design and on heat transfer.

• Can AR 203 and AR 204 be used for very hot exhaust components?

  Only within the permissible temperature range of the probe being used.

  For the AR 204, the supplied surface probes are specified only up to +500 °C.

  The upper measurement range limit of the handheld device (+1350 °C) should not be confused with the temperature rating of the standard probes.

• Why is the probe's measurement range more important than just the device's measurement range?

  Because the entire measurement system may only be used within the permissible limits of its components.
  
  For example, a handheld device may be capable of displaying +1,350 °C, while the connected probe is rated only for +500 °C.
  
  In that case, the probe limits the specific application.

• Can a digital thermometer replace a thermal imaging camera?

  No.
  
  A digital thermometer takes precise measurements at one or a few specific locations.
  
  A thermal imaging camera, on the other hand, displays the temperature distribution across a surface.
  
  Contact thermometers may offer advantages for obtaining precise readings at selected points; for the rapid visualization of larger areas, a thermal imaging camera uses a different measurement principle.

• Can the devices be used on the go?

  Yes.
  
  Both devices are compact, battery-powered handheld meters and come with a carrying case. This makes them ideal for mobile diagnostic and service work.

• Which digital thermometer is best for a multi-brand auto repair shop?

  That depends on the intended application.

  If the primary goal is to quickly check individual temperatures, the AR 203_LR with a combination probe is the simpler, more versatile solution.

  If temperature differences between two measurement points are frequently relevant—especially during HVAC and thermal diagnostic work—the AR 204_LR, with two Type K channels and a differential function, offers more options.

• What diagnostic devices are useful to use alongside a digital thermometer?

  Depending on the application, temperature measurement can complement, for example, cooling system testers, test and diagnostic equipment for automotive air conditioning systems, engine lubrication & oil service, test and diagnostic equipment for turbochargers, or compression pressure testers.

  You can find additional mechanical test and service equipment under Test, diagnostic, and service equipment for internal combustion engines.