February 22, 2024

Back in the days of slant sixes and turbo-fire V8s, one of the easiest ways to distinguish a luxury car from its less-expensive counterpart was to check out the dashboard. The more lights, the more expensive the vehicle. At the other end of the price scale were vehicles like the Ford Falcon, whose cost-conscious design called for a single light bulb in the dash to illuminate both left- and right-hand turn-signal indicators.

As years passed, discerning motorists came to realize that the “idiot lights” on the dashboard weren’t all they were cracked up to be. All too often, by the time a light indicated a problem, it was too late for the driver to take corrective measures. In effect, these lights didn’t tell the driver what was happening so much as what had already happened. Hence, the birth of a new trend: the more posh a vehicle was, the more dashboard gauges it had.

Unfortunately, OEM gauges-when they’re present-tend to be marvels of ambiguity. Constrained by both cost and styling considerations, they rarely have enough graduations or accuracy to give you more than vague clues about what’s going on under the hood. How hot is your engine running? If the answer is “two-thirds of the way between the yellow and red bars,” you might want to rethink your gauges.

For this reason, aftermarket gauges are one of the most popular upgrades on tow vehicles and motorhomes, not only to supplement factory-installed devices but to supplant them entirely.

Watch the Needle
Many gauges are offered in both mechanical and electrical versions, and the distinction between the two is important. While most mechanical gauges directly convert temperature or pressure to the physical movement of a needle on a dial face, electrical gauges first convert it to a voltage or current before converting it yet again to the needle’s physical movement. This last conversion step is typically accomplished either by electrically heating a piece of metal that expands and contracts to move the needle or by using an electromagnet that pulls the needle against an opposing clock spring.

Getting accurate, consistent needle movement with these two techniques is difficult, and this typically makes electrical gauges less accurate than their mechanical counterparts. Also, mechanical gauges tend to respond quicker to changes in pressure or temperature and are unaffected by voltage fluctuations in the vehicle’s electrical system.

Even so, electrical gauges have several important advantages. First, they’re usually easier to install, simply because electrical wiring is easier to route through tight spaces than the copper or plastic capillary tubing used in most mechanical gauges. Second, in the case of oil or fuel pressure, they don’t bring engine fluids inside the vehicle. (For safety reasons, mechanical fuel-pressure gauges usually require the use of a fuel-to-inert-fluid isolator, which must be mounted outside living areas.) Finally, while most mechanical temperature gauges are permanently attached to their sending units by a specific length of tubing, electrical gauges can be located any desired distance away from their senders-a particular advantage in rear-engine motorhome applications.

For these reasons, many folks prefer electrics over mechanicals-or at least some mixture of both. Fortunately, gauge manufacturers often sell mechanical and electrical versions with identical appearances, making it easy to mix and match without sacrificing aesthetics.

Recently, digital gauges have become available in the aftermarket. Most of these designs use the same basic type of sending units as their electric counterparts but convert the sender’s electrical signal to digital data that’s shown on
a liquid-crystal display (LCD). This approach provides most of the advantages of electric gauges, without the loss of accuracy associated with converting an electrical signal to mechanical movement of a needle on a dial face. Some digital gauges still retain a mechanical dial but use the data to drive a stepper motor that precisely controls the needle’s deflection-an approach that combines the accuracy of digital circuitry with the visual appeal of “real” dials.

Gauge resolution is another important consideration. Inexpensive gauges tend to be marked with few graduations, sometimes with a few color bars in lieu of any actual numbers. Better-quality gauges will be marked every few degrees of temperature, every few pounds of pressure and so on. Most top-quality gauges also display their readings over a wide-sweeping meter face, making it easier to read actual numbers at a glance. Naturally, gauge size also plays an important role in resolution: readings are easier to see on a larger gauge, and a large gauge face provides room for the manufacturer to include more graduations.

One’s Never Enough
Aftermarket gauges tend to be installed in pairs or groups. After all, engine and drivetrain performance can be monitored in a host of ways, from rpm to temperature to fuel pressure, so consumers eager to get a full picture often don’t settle for one. After all, the installation of one gauge presents a convenient opportunity to install several others at the same time.

However, on many vehicles, finding sufficient dashboard space for mounting several gauges can be difficult. Aftermarket gauge manufacturers have partially solved this problem by offering “pods” or “pillars” that replace the vehicle’s original windshield pillar cover on the driver’s side, thereby allowing two or three gauges to be mounted in this location. Aside from providing excellent visibility, pillar mounting avoids any cutting or drilling in the dashboard itself. Gauge pods and pillars are available for most current pickups and SUVs, as well as some passenger cars.

A few manufacturers also offer instrument-cluster upgrades for certain vehicles. Basically, these packages allow you to pull the entire set of factory-installed gauges out of the dashboard as a single unit and replace them with an enhanced gauge suite that retains the original unit’s mounting footprint and aesthetics.

Multi-Function Monitors
Most modern engines employ at least one computer to control engine operation. These little brains rely on sensors that measure things like coolant temperature, fuel pressure, camshaft position and absolute manifold pressure. Many vehicles have a second computer to control various transmission functions, with sensors to measure fluid temperature, tail-shaft speed and line pressure, among other things. Typically, the readings are available on the vehicle’s data bus, which transfers data from the computer to peripherals.

Today’s sophisticated gauges allow RVers to use this wealth of data to display a wide variety of functions. Indeed, many monitors are capable of using several pieces of basic data to display more complex information. Need to know your rig’s instantaneous or average fuel economy? Some monitors compute fuel-injector duration and vehicle speed to determine these figures for you. With the help of the aforementioned LCD screens, most models can either display several functions simultaneously or quickly switch between functions at the push of a button.

Since the monitor requires only a few connections to the vehicle’s data bus (with no new sensors or senders to install inside the engine compartment), installation is quick and straightforward. In some cases, this also allows the monitor to be removed and relocated to another vehicle at trade-in time, leaving the old vehicle unscarred by its removal.

Moving a heavy RV down the road puts big demands on the engine and drivetrain and requires extra driver diligence in maintaining proper temperatures, pressures and fluid levels. In this regard, a comprehensive suite of accurate, reliable gauges (or a monitor with similar capabilities) is cheap insurance against unexpected mechanical breakdowns, trip delays and repair expenses.