Mechanical vs. Electrical Automotive Gauges
Find out which gauge type is better, mechanical or electrical.
There are two primary types of automotive gauges - mechanical and electrical.
Mechanical Gauges for Cars and Trucks
Mechanical type gauges use a hard connection between the sensing point and the actual gauge itself.
For example, a mechanical engine oil pressure gauge will have a hard line, typically nylon or copper, between the sensing point and the gauge itself.
As another example, a mechanical engine coolant temperature gauge has a sensing tube (typically a bourdon type) between the sensing point and the gauge.
Electrical Gauges for Cars and Trucks
Electrical gauges use a sending unit or transducer to convert the process measurement into an electrical signal that the gauge then reads.
So in the example of the engine oil pressure gauge, the sending unit would be installed at or near the sensing point, then the wires from the sending unit would be connected to the gauge. The gauge would then provide the readout based on the electrical signal from the gauge sending unit.
Comparison of Benefits of Mechanical and Electrical Gauges for Cars and Trucks
So how do you choose a mechanical type of gauge or an electrical type of gauge? It depends on what your goals are. Here we will list some parameters of electrical and mechanical gauges for comparison:
Cost
Mechanical type gauges are typically less expensive than their electric counterparts, particularly full sweep electric gauges. An execption in some cases will be fuel or other pressure gauges where a pressure isolator is required (discussed in more detail under the Sending Unit section below.
Gauge Installation: Wiring
Electrical gauges obviously will require more wiring than mechanical gauges. The only wiring typically required for a mechanical gauge is if it has a backlight and you want to connect the backlight to say the parking light circuit. Now an electrical gauge will usually have this backlight feature as well.
Gauge Installation: Mechanical
Mechanical gauges require routing the sensing tube or other hard link between the gauge and the sensing port. If there are many tight bends or it is being routed behind the dash without removing the dash, the installation can be tricky. Also if the tube is not long enough, it can be difficult to extend it to reach. Or if it has a fixed tube such as in temperature gauges, the extra tubing must be coiled up or otherwise dealt with.
With electrical gauges, there is just wiring between the gauge and the sender or sensor. It can be easily cut to length as needed and can make tight bends.
Gauge Installation: Sending Unit
As we already examined briefly, mechanical gauges have tubing or other mechanical link that runs from the sensing port to the gauge.
Electrical gauges have a sending unit, transducer or transmitter at or near the sensing point, and then wiring is routed from the sending unit to the gauge.
Typically the sending unit for a mechanical gauge will be smaller and easier to install than a mechanical gauge. For example, for an oil pressure gauge, it is just a piece of tubing to install, so it can fit into a tight clearance area. For electrical oil pressure gauges, a pressure sender about 1.5" diameter by 3 inches long must be installed. If there is not enough space to fit the sender directly into the sensing port, then a length of tubing between the sensing port and sender may be needed. This extra length of tubing isn't necessarily expensive, but it does add to installation difficulty and adds a possible point of future failure.
Mechanical Pressure Gauge Risks
For pressure gauges such as engine oil pressure and fuel pressure, the main risk is that if the tubing between the sensing port and the gauge ruptures, breaks or springs a leak, the process fluid is going to start spraying.
This leaking fluid could cause a dangerous situation. For example hot (say 200 deg. F) engine oil sprayed in your eyes is going to make it hard to keep your eyes open while driving. Ditto for gasoline. And these both can cause a fire.
Pressure Isolator
Pressure isolators are available to isolate the direct mechanical link between the sensing port and the gauge. These pressure isolators typically have a flexible chemical resistant membrane to transmit the pressure, but prevent any actual flow of the process fluid. A pressure isolator is required for mechanical fuel pressure gauges where the gauge will be mounted inside the passenger compartment.
Gauge Stock Availability
Sometimes a vendor will be out of stock of the particular model gauge you want in for example the electrical version, but have it in stock in the mechanical version. So if you are not willing to wait for the gauge to be backordered, that might tilt the decision toward the in-stock gauge.
Gauge Type Availability
Only certain types of gauges are available as mechanical gauges. Typically pressure gauges and temperature gauges are available in both mechanical and electrical versions. However certain gauge types such as voltmeters, ammeters, and air/fuel ratio meters by their very nature are available in electrical versions only.
Data Logging
If you want the option to log data directly from the gauge, electrical gauges are the way to go.
Digital Gauges
If you would like your gauges to have a digital readout, obviously only electrical gauges are available with digital displays. These types of gauges usually also support data logging and may have an adjustable setpoint at which the display will flash or make a sound.
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