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 to your engine if it overheats.
In this article, we will talk about the coolant temperature gauge and what you can do if this issue occurs.
7 Causes of Car Temperature Gauge Stays on Cold
The most common reason why your car’s temperature gauge stays on cold is a faulty coolant temperature sensor. It can also be caused by bad wiring between the cluster and the sensor. In some cases, it can also be a stuck thermostat causing the engine not to heat up properly.
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.
1. Faulty Engine Coolant Temperature Sensor
As we talked about, the most common problem with 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 for them. You can also 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 to replace the sensor going to the temperature gauge – if you have two.
2. 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.
3. Faulty Gauge/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 do it yourself.
A faulty cluster is not a very common problem, though, and they are often pretty expensive and need programming 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.
4. Corrosion in plug connectors
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.
5. Bad Thermostat
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
6. Air in the Cooling 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.
7. Broken 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.
Frequently Asked Questions
Is it bad if my car temperature is cold?
Yes, if your thermostat is stuck open and the engine never gets up to operating temperature, it’s bad for the engine and fuel consumption in the long run. The car engine is most efficient when it reaches operating temperature and it will also wear less on the engine parts.
How do you unstick a stuck thermostat?
The only way to loosen a stuck thermostat is to do it manually by removing it. But if your thermostat is stuck, you’ll most likely want to replace it, or you could end up in the same situation in the near future, and they are quite inexpensive.
How do I know if my thermostat is stuck open?
One way to tell if the thermostat is stuck open is to check the outlet radiator hose. The hose should not have any coolant circulation while the engine is warming up and therefore should remain cold until the engine reaches operating temperature. If it is the same temperature as the inlet hose during the heating process, it is probably stuck open.
How do I reset my temp gauge?
There is no way to reset your temperature gauge in most car models. If you have a rare car model where it’s possible you need to check a repair manual for your particular car model.
Conclusion: Temperature Gauge Stays On Cold
The temperature gauge staying cold is a serious problem that needs to be fixed. This can be done by checking the cooling system, engine components, and electrical system. It’s not good for your engine to drive around your car without reaching the operating temperature in the long run.
The main reasons a temperature gauge stays on cold include:
- Faulty Engine Coolant Temperature Sensor
- Broken Wirings
- Faulty Gauge/Cluster
- Corroded Plug Connectors
- Bad Thermostat
- Air in the Cooling system
- Broken Engine Control Unit
If you are not comfortable doing this yourself, take it to a mechanic or dealer. With proper care and maintenance, your car will last longer and perform better.