Are you having problems with your coolant temperature gauge staying on cold, even if the car engine obviously is warm?

One of the most important things to keep track of in your car is the coolant temperature because some horrible things can happen with your engine if it overheats.

In this article, we will talk about the coolant temperature gauge. What could cause the temperature gauge to stay on low?

7 Causes of Car Temperature Gauge Stays on Cold

  1. Faulty engine coolant temperature sensor
  2. Broken wirings
  3. Faulty gauge or instrument cluster
  4. Corrosion in plug connectors
  5. Bad thermostat
  6. Air in the cooling system
  7. Broken engine control unit

These are the absolute most common reasons why your car temperature gauge stays on cold. Let’s go a little bit more into detail about the different causes.

Here is a more detailed list of the most common causes when a temperature gauge stays on cold.

Faulty Engine Coolant Temperature Sensor

Coolant Temp Sensors

The most common problem when it comes to a faulty engine temperature reading is the coolant temperature sensor itself, sending the information to the cluster.

Some cars have two temperature sensors, while other car models have one. The models with one sensor usually both use the engine control unit’s temperature and the same sensor for the gauge.

If your car model has two coolant temperature sensors, one is used by the temperature gauge, and one is used for the engine control unit.

Engine temperature sensors are easy to measure with a multimeter, but you need to find the right values of them. You can often find more information on how to test them in your repair manual.

However, if you decide to replace one of them, you should make sure that you replace the sensor going to the temperature gauge – if you have two.

Broken Wirings

Broken Wirings

If you have two temperature sensors on your car and one separate for the gauge, you need to check the sensor’s wires to the gauge or ohm measure the sensor from the cluster connector.

If you have one sensor for both of them, there could either be a problem with the wires between the sensor and the ECU (most likely) or a wiring problem between the gauge and the ECU. Check for any broken wires between these components.

The best way to find broken wiring is to measure the resistance with a multimeter from all the wires’ directions. However, this requires a bit of electronic car knowledge, and you may have to let your mechanic take a look at it. 

You can also find information about this in your repair manual. Check a wiring diagram of your car to measure the wiring correctly.

Faulty Gauge/Cluster

Instrument Cluster

The next problem is a faulty temperature gauge. However, most temperature gauges are integrated with the instrument cluster on modern cars. In some cases, you can replace the temperature gauge or repair any bad solderings if you find any.

In other clusters, you might have to replace the instrument cluster. You can often leave your instrument cluster to an expert to repair the soldering if you do not know how to yourself.

A faulty cluster is not a very common problem, though, and they are often pretty expensive and need coding after replacement. Therefore it is recommended to check the other things first before you decide to replace the cluster.

You can also test the cluster temperature gauge with an Ohm tester if you have some knowledge.

Corrosion in plug connectors

Coolant Temperature Sensor Location

Corrosion in the connectors is also a common problem when it comes to a faulty temperature gauge. Clean and spray electronic cleaner in the connector at the sensor, the engine control unit connector and the cluster’s connector.

If corrosion appears, there might be a problem with the connectors’ sealings, and you may have to take a look at these to make a permanent repair or replace them to avoid future problems.

Bad Thermostat

Thermostat Housing

The thermostat restricts the coolant from flowing through the radiator. If this gets stuck on wide open, the temperature might not reach the optimal temperature.

However, this will often make your temperature go up a bit from the min mark if you drive hard enough. If your temperature gauge is going up slowly, you might have a problem with the thermostat. 

You can read more about thermostats here: Faulty Thermostat Symptoms & Causes

Air in the Cooling system

Bleeding Coolant System

Air in the cooling system can also cause the temperature gauge to stay cold if there is an air bubble right at the sensor spot. This can also often be indicated with a fluctuating coolant temperature gauge.

If you suspect air in the coolant system, you have to bleed your coolant system with a unique bleeding technique. If you want to learn more about this, you can check out our guide: Coolant Bleeding.

Broken Engine Control Unit

Engine Control Unit

This only applies if your car uses one combined temperature sensor with two pins.

In some rare cases, your engine control unit could be a problem if the temperature information is received first to the ECM, which therefore sends the data to the cluster.

If this is the case, you have to check the trouble codes with an OBD2 scanner in the engine control unit to see if the engine control unit receives the temperature information. 

If you can find the temperature readings in the engine control unit but not at the cluster, you have to make sure that they are using the same sensor. If this is the case, you have to measure the temperature output on the engine control unit. To do this, I recommend letting a car electronics expert do the job for you. 

You do not want to replace the engine control unit if there’s no problem with it because they’re often costly and require coding.