Tachometer Buyer’s Guide
- A tachometer measures the rotation speed or revolution per minute (RPM) of the engine crankshaft.
- Redlining is when you go beyond the recommended operating speed of your engine. It is usually indicated by the red area in your tachometer.
- Automatic transmission vehicles have computers that shift gears and prevent redlining, making tachometers unnecessary and purely for aesthetic purposes.
- There are several types of tachometers. They can be digital or analog, contact or non-contact, and time measuring or frequency measuring.
- LED display failure and erratic readings are two common symptoms of a faulty tachometer.
- The price range of aftermarket tachometers depends on your car’s year, make, and model as well as other factors such as colors, styles, bezels, and features.
What is a tachometer?
A tachometer—also called rev counter, tach, revolution counter, RPM gauge, and tachometer gauge—is a device that tells you how fast your engine is moving. You can typically see it on the left side of your dashboard next to your speedometer. Its main function allows the driver to monitor and assess the engine speed and change gears accordingly.
German engineer, Dietrich Uhlhorn, was widely recognized as the inventor of the first tachometer in 1817. He needed a device to measure the speed of machines. This same device became a standard feature on every vehicle some 200 years later.
How does a tachometer work?
A tachometer measures the rotation speed or revolution per minute (RPM) of the engine crankshaft, which is then displayed on your dashboard while you’re driving. The device usually has numbers ranging from zero to nine with multiple markings or lines between the numbers. Each number—multiplied by a thousand—represents the engine’s RPM. So if the indicator or needle is on four when you are driving, it means that your vehicle’s crankshaft and tires are hitting 4,000 rotations per minute.
There is also typically a red area on a tachometer. If the indicator or needle is on the red area, it means that you are reaching the maximum RPM for your engine and it is recommended that you switch gears to avoid redlining. Staying on the redline section on your tachometer for too long may cause serious damage to your tires and engine. The valve train (responsible for the flow of gas to and from the combustion chamber) and transmission may also take a hit over time from consistent redlining. Both of these parts are not only expensive but also difficult to repair. If you are driving a car with manual transmission, it’s easy to redline whether it is accidental or on purpose so you must always pay attention to your tachometer.
What’s the purpose of a tachometer in an automatic transmission vehicle?
Because a tachometer practically assists the driver in shifting, it plays an important role in a manual transmission car. In an automatic transmission car, the shifting of gears is computerized and requires no help from the driver, so a tachometer becomes unnecessary. The engine is also prevented from redlining through the use of a rev limiter, which cuts fuel flow through the fuel injectors or fuel rail and/or disables the ignition system to lower the engine speed.
Simply put, a tachometer in an automatic car is purely for aesthetics. Although modern cars offer a fully customizable dashboard, you might find it weird to see the speedometer without the tachometer. Some drivers, however, have found a practical use for their tach. They use it to quickly check if their engine is running since more and more cars today make very little noise at idle.
Types of tachometer
Analog and digital tachometers
An analog tachometer is composed of a needle pointer and a dial. The needle moves in accordance with the car’s speed. It has no storage of readings and cannot compute and provide other details such as average and deviation.
A digital tachometer has an LCD or LED display and has a memory for data storage. It offers more precise measurement and monitoring when compared to an analog tachometer. Some digital tachometers simply display numbers for the RPM, but others have adopted a more visual display like an analog-type round dial with a needle and horizontal or vertical bars to indicate the measured RPM.
Contact and non-contact tachometers
A contact tachometer is in direct contact with the part that it is measuring, which in this case is the rotating shaft. With the part and the sensor rotating at the same speed, it’s guaranteed to provide accurate data. It often uses a magnetic sensor or optical encoder. A non-contact tachometer, on the other hand, uses a laser to illuminate a mark on the rotating part. The movement of the mark is then detected by a light sensor on the tach.
Time and frequency measuring tachometers
Tachometers can also be categorized based on their measurement methods. Time measuring tachometers determine speed by measuring the time between incoming pulses while frequency measuring tachometers measure their frequency.
Symptoms of a faulty tachometer
Your tachometer might not work properly for several reasons, but most of them can be categorized into mechanical and electrical problems. What’s more important is to be able to tell when your tachometer is having issues. Here are a couple of symptoms you need to look out for:
Tachometer display failure
This is the easiest way to tell that your tachometer is problematic. No reading on your LED tachometer probably means that you have a bad LED tachometer display--which is pretty common in tachometers that have been in use for a long time.
Erratic display of readings
This symptom is trickier because you have to pay more attention to your tachometer readings. If the readings on your tachometer, for example, fluctuate at random times like when you are idling or driving at a constant engine speed, you might have to do some troubleshooting. This may be caused by broken or corroded wire connections, a bad ground, or a simple calibration problem.
How much does an aftermarket tachometer usually cost?
Depending on the year, make, and model of your vehicle, the price of an aftermarket tachometer can range from $50 to $900. You can also choose from a wide variety of colors, styles, bezels as well as features such as full LED dial and perimeter incandescent lighting. Each aftermarket tachometer is sold individually and is usually engineered for easy installation.
CarParts.com can help you find the right aftermarket tachometer for your vehicle. Just select your car’s year, make, and model in the built-in vehicle selector and then search for the part that you need. You will then find all the tachometers that are suitable for your ride in the search results. The process is as easy as one, two, three, so you can quickly find what you’re looking for.
Tips When Shopping for a New Tachometer
Positioned directly on your car's dashboard, a tachometer is a gauge that shows the engine's crankshaft revolution per minute or RPM. This assists you when to change gears at the right time. If your car already has a faulty tachometer, there's a risk of engine over-revving because you won't be able to determine the redlining or the maximum safe limit. Don't let your car stay at risk, here's a tachometer buying guide to help you find the right one.
A comparison between analog and digital tachometers
This type of tachometer is what you'll see in most cars. It's inexpensive compared to a digital tachometer, which makes it a good choice for a street car. An analog tachometer uses a needle to indicate the RPM reading. It can be difficult to read precisely, but it does show the distance of the needle to the red zone.
A digital tachometer displays precise numbers of the RPM. This information is very crucial for race cars. A digital tachometer can even store data which is used for engine tuning. It can show graphs that analyze car performance, and it has a LED that lights up when gear shifting is already necessary. In spite of these things, some digital tachometers require batteries. This is very critical and time-consuming because you have to replace the batteries regularly, or be ready when it suddenly stops.
- Analog tachometer
- Digital tachometer
Both analog and digital tachometers practically perform the same purpose. It would be a matter of how you want to view the RPM, and use the performance data, which gives the digital tachometer a slight advantage.
Other things to consider when buying a new tachometer
It's not because a lot of tachometers are sold nowadays that you can already buy one in a snap. Check your engine first if it's applicable to the tachometer because manufacturers specify the number of engine strokes and cylinders.
The dashboard of your car already contains a tachometer by factory default. If you'll install an aftermarket tachometer, you should consider the size and the location of the tachometer. Regular tachometers range from 3-5 inches, so at least you have an idea.
For those who choose a digital tachometer, you have to consider if data is programmable and easy-to-use. You have to know the storage capacity as well, so you can save information for the next tuning.
- Your car's engine
- The size
- Data features
Auto Repair: Installing a New Tachometer
A tachometer is a gauge that shows the RPM reading of your vehicle. To replace a broken "tach" will mostly involve wires, and this task is an easy fix especially if you have a complete set of tools in your garage. This guide will show you how to do it in just nine simple steps.
Difficulty level: Moderate
- Drill set
- Car manual
- Wire stripper
- Wire connectors
- Electrical tape
- New tachometer
Step 1: Take the new tachometer and the hardware from the box, and check their conditions. If everything is good, set the tachometer depending on the number of cylinders your car engine has. Refer to the instructions that came with the box if you're uncertain.
Step 2: Find a place where you'll mount the tachometer. Make sure that the mounting brackets will fit on the surface, and the wires will still reach the tachometer.
Step 3: Drill the holes for the mounting brackets, and mount the tachometer. Seal the position using the screws or bolts.
Step 4: Connect the red wire from the tachometer to your car's fuse box, but do not seal them yet. Refer to your car manual to know which terminal can be used for a tachometer. If the wire from the tachometer is not red, then check the instructions to know which wire should be connected to the car's fuse box.
Step 5: Remove about a half-inch of insulator from the red wire. Take the wire connector, wrap the electrical wire around it, and attach it to the terminal.
Step 6: Connect the tachometer's white wire to the harness that leads to the instrument lights. Splice the wire afterwards with a wire connector, and clamp the two sides on the white wire and the instrument lights. Connect the two sides by clamping the metal wires. Use an electrical tape to secure the wires.
Step 7: Take the green wire from the tachometer, and connect it to the coil's negative terminal. Use the connector to bolt the wire to the coil.
Step 8: Route the tachometer's black wire into a metal ground around the engine. Use the connector attached to the black wire to fix it in position.
Step 9: Turn on your engine to check if the tachometer is already working.