Install an Aftermarket Coolant Gage in Your Car

Almost all modern cars with an internal combustion engine require coolant (also known as “anti-freeze” to cool the internal components of the engine. A coolant temperature gauge tells you the temperature of the coolant, so the driver knows if they need to let the car warm up before accelerating aggressively, or if they need to back off the throttle if the engine is overheating. The purpose of this WikiHow is to show how a car can be fitted with an aftermarket coolant temperature gauge. You may need to do this for a variety of reasons:1) The coolant gauge that came with your car is broken and beyond repair2) The car has a custom modified engine configuration in which the factory coolant gauge no longer works, for example, putting a Chevrolet engine in a Toyota car. 3) The car never came with a coolant gauge or is not accessible easily by the driver.4) The car does have a temperature gauge but is not very accurate. Most cars from the factory will display that the temperature is “all good”, even though it isn’t in order to keep the driver calm.


  1. After purchasing your kit, lay out the parts from the kit and become familiar with the names of all the components. When purchasing the kit, ensure that is it compatible by consulting the manufacture of the gauge. Due to licensing issues we cannot show you an actual kit, but the owner’s manual of the kit will show a diagram will all the parts labelled.
  2. Locate the engine’s existing coolant sensor port. This is typically located on the cylinder head, because of the wide variety of engine configurations, it is best to confirm the location of this sensor using a repair manual specific to your car/engine.  
  3. Remove the sensor with a wrench, confirm the size before applying pressure.
  4. Install the “1/8-27 NPT Temperature Sensor” from the kit. To do this, spin the sensor into the port gently by hand. This should not require a lot of twisting force, if it does, ensure the engine and temperature sensor are clean, and that the sensor is the right size. Once it is tight by hand, use a wrench to tighten the sensor until it is snug.
  5. Understand the wiring from your kit since they are all different. Generally, there will be about 4 wires that come out of the gage, but this can vary, along with the colors. Understand their operation below, then route the wires. The routing of the wires will depend on the vehicle, it is usually best to use an existing wire grommet. If you are unsure on where these might be, consult the vehicle’s service manual. Use solder and electrical tape or high-quality automotive crimps to connect the wires. If you are unsure how to do this, WikiHow has several articles. Just search, “How to Solder” or “How to crimp”. If you need to extend the wires, use standard automotive grade 18ga hook up wire.   
    • Yellow Wire: Power – This goes straight to the positive post of the battery through a fuse.
    • Black Wire: Negative – This goes straight to the negative post of the battery or an unpainted, metal structure on the vehicle.
    • Orange Wire: Goes to the power line off the headlight, this is so that when the headlights are turned on (when it gets dark), the gage will automatically reduce the brightness on the screen. This wire is optional and may not be included with every kit. To find this wire, consult the car’s factory service manual wiring diagram, and perform a wiring splice. If you are insure how to do this, WikiHow has serval articles on wiring, just look up “How to splice wire”
    • Green Wire: This goes to the white wire coming out the temperature sensor installed in Step 4. There will usually be a black wire coming out of the sensor, this needs to go to the negative post of the battery, or, more conveniently, any good, clean ground connection which is any clean unpainted metal structure on the car. This can be done by crimping a ring terminal on the wire, and installing it onto an existing bolt on the car.
  6. Install the gage and connect the wires you routed in step 5. Most gages have several ways they can be mounted, usually there is an included bracket where you can drill holes into your interior and screw them on. Otherwise, they are fixed with double sided tape. Consult the kit’s manual on the specifics of your gage.
  7. Start the car’s ignition, but do not crank the engine yet. In most cars this can be done by turning the key one click without your foot on the brake or clutch. This will turn all the electronics on without starting the engine. This step is to double check your wiring, the gage should be reading the absolute minimum value.
  8. Open the coolant cap and refill any coolant that was lost. Coolant filling procedures can vary greatly based on the type of car and how much coolant was lost. Consult your car’s service manual to make sure the coolant was filled properly. WikiHow also has instructions on ths, just search “How to check coolant”.
  9. Start the engine and allow it to get to temperature. While the car is warming up, look for leaks, specifically where the sensor was installed, then, check that the temperature gage is reading accurately. It should start to rise slowly and plateau around 100c/212f, however this will vary on the car’s operating temperature. Look for steam as well, some steam may be normal as it is coolant that was spilled during the procedure, and not its contacting the hot engine, however a lot of steam may indicate a continuing leak.


  • Purchase a service manual for your car, including a wiring diagram.
  • Study the installation manual of your gage kit, and contact the manufacturer for compatibility before purchasing.


  • CAUTION When removing the sensor, coolant will start to leak out, be ready to collect the coolant in an appropriate container and keep it away from animals and children as it is toxic if ingested. Allow the car to sit for several hours before performing this to ensure the engine is cool to the touch to avoid burns.CAUTION