The Truth About Mechanical, Electrical, and Stepper-Motor Gauges

Long before muscle cars were even built, automakers needed a way for drivers to monitor engine functions in their daily transportation. Gauges were developed from simple-operating devices like an Ammeter gauge to make sure the battery had juice and a fuel gauge so you didn’t get stuck along-side the road.

As cars became more technically endowed, more gauges were added to the dash. It didn’t take long until dash clusters with voltage, fuel levels, oil pressure, water temperature, speed, and tachometers were facing drivers. Way back in 1957, Vern Westberg realized that automobiles could use a more accurate monitoring system, and AutoMeter was founded.

gauges

Whether you’re building a custom dash or just adding a few gauges under your existing dash, you have choices.

When you hop behind the wheel of your hot rod, other than the power of your engine, what is something that you really notice? Hopefully, you said the gauges. You do watch your gauges so your engine doesn’t melt-down, right? When you are either in the process of building or updating your ride, you have to decide what gauges will best work for your application. Not only do you want to consider cost, looks, and size, but whether to install electric or mechanical-style gauges. We all have at least one buddy that swears he will only use mechanical gauges – because they have to be more accurate. We wondered if that were actually true. That was one of the questions we posed to Joseph Mills of AutoMeter, so we could get some honest information that enthusiasts should consider when deciding to choose aftermarket gauges.

gauges

Mechanical pressure gauges – like this oil pressure gauge – use a tube that fills with the fluid being monitored. A huge down-side is if the tube breaks inside your car, you have mess to clean up.

Electrical, Mechanical, Or Something Called Stepper Motor?

For years, if you were contemplating aftermarket gauges, your only two choices were either electrical or mechanical. Both offer a good design, but there is still that old connotation that mechanical gauges are more reliable and more accurate than electrical. Once and for all, that simply isn’t true. To add some confusion to the available choices, there is a (relatively speaking) new kid on the block: the Stepper-Motor gauge. These high-tech instruments are controlled by a microprocessor on a circuit board, not a capillary tube or magnets like mechanical or electrical gauges. But, if all three gauges are considered equal, how do you know which you should use?

“A lot of it comes down to personal preference. We still sell a lot of mechanical gauges, though I greatly prefer using an electronic for something driven on the street. A lot of old-school guys came up in a time when mechanical gauges were significantly better than electronic ones. That hasn’t been true for a long time. I prefer the ease of installation an electronic gauge affords you.” Joseph continued, “I’m also not huge on running fluids into the passenger compartment. For a more extreme build or something with a lot of engine, I’d definitely move toward the digital Stepper-Motor gauges. While they cost a bit more money, it’s cheap insurance. Especially when you start to add up what it cost to put your engine together.”

gauges

Mechanical temperature gauges rely on a capillary tube with a bulbous end that connects to the engine.

Electrical Gauges

An electronic gauge functions by use of a small magnetic core wrapped with copper that will move in relationship to the voltage it receives. This voltage is regulated by the sending unit, which will change its resistance-to-ground, based on the pressure it is receiving. As the temperature or pressure changes, the resistance varies, moving the indicator to a calibrated position on the dial. These gauges are physically different from mechanical and Stepper-Motor gauges, and use a short sweep reading.

I prefer the ease of installation an electronic gauge affords you. – Joseph Mills, AutoMeter

“A typical AutoMeter electronic gauge is going to be no worse than +/- 5-percent accurate at full deflection. This is less than the width of the pointer, so given the dial resolution, any variance is almost academic,” Joseph stated.

Pros: Inexpensive, easy to install, great real-world accuracy, very durable.

Cons: Not as accurate as a Stepper-Motor gauge, limited pointer sweep.

Mechanical

These gauges have a direct connection (via a tube or capillary) to the engine. Take for instance an oil pressure gauge. It has a plastic or copper oil tube from the back of the gauge that connects to the engine. A temperature gauge will use a long capillary tube – similar to an old-style glass thermometer – that is mounted into the engine. The bulbous protrusion on the end of this tube is heated by the engine fluid, and an ether gas encapsulated within the tube expands, pushing the meter movement forward and displaying the temperature.

An advantage to mechanical gauges is they can be utilized without being connected to the car’s electrical system. This is great for a race car, as when the car is shut off in the pits, the gauge will still display the current temperature. Some feel that electric gauges are better, because the fluid-filled lines of a mechanical gauge can rupture. Remember, this line, hose, or whatever you want to call it, is running inside your car.

“An AutoMeter mechanical gauge will be a little more accurate, not really exceeding +/- 2-percent at full deflection. The increased sweep, and therefore, dial resolution, also aids in visibility,” Joseph remarked.

Pros: Great accuracy, full dial-sweep, always on, has a direct, physical connection to engine.

Cons: Can be harder to install, introduces fluid in the passenger compartment.

Digital Stepper-Motor

The next type of instrument we’ll touch on is fairly new to the automotive world: Digital Stepper-Motor gauges. These highly advanced gauges provide the highest possible levels of accuracy, precision, response, and durability. “The digital Stepper-Motor electronic gauges are the most accurate, with a typical variance of +/- 0.5-percent. These are also the most durable gauges and use the same solid-state sending units as our high-end data systems, which are a big upgrade from standard senders,” Joseph stated.

gauges

The Stepper-Motor gauge is the latest evolution in gauge design. It utilizes microprocessors for operation.

Stepper-Motor gauges are controlled by a microprocessor that utilize laboratory-grade sending units for the ultimate in accuracy. An added bonus to choosing a Stepper-Motor gauge is that any of the sending units can also be used to provide data streams to a data logger or standalone engine management system. Mechanical and electronic gauges can cause concern for some enthusiasts when the gauge needle doesn’t return to zero. This is not an issue, just a fact of operation and supplied voltage. With a Stepper-Motor gauge, every time the gauge is powered, it will zero calibrate. This ensures that over the gauge’s lifetime, it will always remain as accurate as it was the day it was built. These gauges utilize 270 degrees of the dial, making them very easy to read.

Since the Stepper-Motor gauge is, well, a circuit board, we asked about failure rates. “Anything is possible, but it’s highly unlikely. I suppose if our gauges never broke, we wouldn’t have a warranty, but our across-the-board failure rates are in tenths of a percentage, and the Stepper-Motor gauges are even more robust. I wouldn’t expect any issues with one of those over the life of the vehicle,” Joseph stated confidently.

Pros: Best possible accuracy, durability, and easiest to install. Available with advanced features like warnings, recall, and electronic-device control.

Cons: A bit more expensive.

Is an Electric, Mechanical, or Stepper-Motor Gauge Easier To Install

There is little difference in the work involved to install any of the gauges, as it will likely take you about the same amount of time for each. However, routing of the mechanical gauge’s tubing will require a bit more planning. That’s because you will need to be careful so you do not kink or damage the line as you route it from the engine to the gauge. You will also want to make sure that the line is as short as possible to get the most accurate reading. With an electronic or Stepper-Motor gauge, as long as you get the wire connected, the gauge will work fine.

High Speed Pursuits

When it comes to speedometers, once again, you have a decision to make. While the tried-and-true cable-driven speedometer does still have a place in the hobby, an electronic mph-meter simply requires you to connect a couple of wires between the gauge and either a Vehicle Speed Sensor (VSS) in the transmission, or a GPS-signal receiver.

AutoMeter

An electronic speedometer will deliver better accuracy, and is more versatile in regard to installation.

Again, your application and budget will determine which is your best choice. For instance, if your car was originally equipped with a cable-driven speedometer, it would probably be cost effective to replace it with another. But keep in mind, your new, cable-driven speedometer could fluctuate and be inaccurate. This is not any fault of the new gauge, but rather, because there is a flexible shaft encased in a plastic housing that extends between the transmission and the speedometer. As it ages, this flexible shaft can bind and stick inside the housing, which causes the fluctuation. Have you ever seen a speedometer bounce from 20 to 100 mph while you drive? If you are planning a new installation using a cable-driven gauge, the flexibility of the cable assembly will limit how it can be routed.

gauges

The small GPS-receiver to the right of the control module can be mounted almost anywhere on the car. It is then connected to the control module, which is then connected to the speedometer.

If you feel the need to update you ride with an electric speedometer while still using a cable-driven system, you can use a Speed Sensor, but the ease of installing an electronic speedometer really makes that option obsolete.

The advent of commercially available GPS signals has impacted gauge design immensely. Now, instead of having a cable running from your transmission to the gauge, or needing a VSS of some sort connected to your transmission, you can simply mount a GPS receiver – almost anywhere on your car – and then connect a couple small wires to the gauge. When it comes to choosing a speedometer, you have a multitude of options.

Autometer

If using a GPS-enabled speedometer, the receiver needs to be mounted in an area where it can receive the satellite signal. That means possibly having the receiver mounted out in the open.

It seems that deciding what gauges will best suit your application is a matter of personal taste. All three of the discussed gauges offer an accuracy that is nearly imperceptible to the human eye, and durability that has an almost equal playing field. The final decision mostly comes down to what you are comfortable using, and how much the final cost will affect your budget.

If you still have questions about gauges, and would like more information, you can check out the AutoMeter website, and/or give them a call at (866) 248-6356.

Article Sources

About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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