The temperature gauge in your car could be the most important gauge on the car. The temperature gauge informs the driver when the engine is overheating, allowing the driver to prevent the engine from being permanently damaged.
When the driver observes the gauge temperature climbing, he or she can pull the car over to the side of the road and allow the engine to cool. But what happens when the car temperature gauge goes from hot to cold?
In this article, we will outline temperature gauge issues, highlight solutions to these issues, and note the importance of diagnostics in this situation.
Reasons Why A Car Temperature Gauge Goes Up And Down
The temperature gauge can fluctuate due to a faulty thermostat, insufficient coolant, or even air in the cooling system.
Here’s a more detailed list of reasons why your car temperature gauge goes up and down:
#1. Bad Thermostat.
The thermostat is used to regulate the temperature for the engine coolant. When it starts to go bad, it will begin to operate erratically, causing the temperature gauge to jump up and down. After it is faulty, it will no longer operate like that.
When the thermostat is stuck closed, it won’t allow the coolant to flow, causing the engine to not cool off. This can create an engine that overheats.
When the thermostat is stuck open, the engine temperatures will drop below normal. It could be hard to get heat from the HVAC system as well.
#2. Low Coolant.
If there is a high concentration of water in the cooling system, the temperature gauge can act funny as well. Some people mix water with the coolant but you have to be careful that there isn’t too much water in the system.
If there isn’t enough coolant in the system, the temperatures will rise. Water does not carry heat away from the engine as efficiently as coolant does – which could show unusual temperature fluctuations.
If the engine starts to run hot, you need to replace the coolant with a water and antifreeze coolant mixture. Follow the required antifreeze to water mixture that is specified in your car or truck service recommendation.
#3. Air in Cooling System.
If you notice the temperature gauge dropping at times, you could have air in the cooling system. Air can enter the coolant system from a defective radiator cap, blown head gasket, or a coolant flush conducted improperly.
An air pocket withholds the coolant and the engine will start to run hot. After it eventually moves through the pocket, the engine temperature will return to normal.
#4. Temperature Gauge Error.
Your temperature gauge’s error may simply be that the gauge itself is bad. Often, you don’t check the instrument cluster first, but it could be the temperature gauge if you did not find anything else wrong.
Often, if the instrument cluster is having an issue, you’ll see other issues too. Look at other gauges to see if it is an electrical issue.
#5. Faulty Coolant Temperature Sensor.
It is more likely the issue is caused by a bad coolant temperature sensor or CTS. The CTS is found in the engine and easily contaminated.
Also, if the CTS gets damaged or corroded, it could send wrong signals. It may also seem to have intermittent readings; it may be shutting or or misreading intermittently as well.
#6. Computer Module that is Bad.
If you are noticing a temperature gauge that is erratic, it could be due to a bad computer module. This is something that will make data communicate in all systems in the vehicle as well with the engine.
It is the module’s job to relay the data that moves the temperature gauge. If the module is going bad, however, you may notice other weird issues, as this part controls a lot of systems.
How to Fix Fluctuating Temperature Gauge
#1. Replace Thermostat.
Replacing a car’s thermostat will cost you between $125 to $300 on average. Fortunately, it’s not that difficult to do yourself.
To begin, locate the thermostat; it is most likely located at the point the top radiator hose connects to the engine and possibly at the bottom hose. Next, remove the clamp and catch any coolant in a bucket underneath.
You can now remove and replace the old thermostat and put a new gasket in place. Replace everything and fill the system back up with coolant.
#2. Fill Cooling System.
Having a professional perform a coolant flush on your vehicle will average between $65 and $150. However, this can be done at home as well.
To perform the flush, drain the radiator and fill it back up with distilled water. Run the vehicle for ten minutes, and after turning off the engine, drain the dirty water from the system, then put fresh coolant into the system mixed as recommended by your automaker.
#3. Bleed Cooling System.
If you notice air getting trapped, bleed the cooling system. Remove the radiator cap and fill it with coolant as much as possible. With the heat set to max and the fan on low, start the engine.
As you start the engine, continue to fill coolant as the level drops. You’ll want to loosen cylinders and each time rev the engine a few times to purge the air out of the system. You want to do this step until the temperature stops fluctuating.
#4. Change Temperature Gauge Sensor or Gauge.
Replacing the temperature gauge sensor costs between $200 and $450. You may need to replace the coolant temperature sensor on the top or side of the engine. It is also possible the gauges themselves are faulty.
Be sure to troubleshoot first, or risk spending money unnecessarily replacing parts.
#5. Change Computer Module.
This is the most expensive repair of all. On average, a new Engine Control Module costs around $300 to $1,500 for parts and labor.
A good code scanner is likely to indicate whether there’s a problem with the Engine Control Module. You might also experience odd symptoms, as this central brain is beginning to fail.
How Does the Car Temperature Gauge Work?
The car temperature gauge shows the operating temperature of the engine. Typically it is located on the dashboard near the speedometer. The function of the gauge is to measure the temperature of the coolant, and it shows how hot or cold the motor is at all times.
The water pump helps to circulate the coolant through the system. While circulating through the engine, it is heated up and then it cools down as it circulates through the radiator.
The thermostat is important to keep the temperature in the proper range. The thermostat controls the flow of the coolant to either stop it or start it. The coolant temperature sensor is also near the thermostat and sends the signal that gauges is reading.
You need to know what the operating temperature is, so you know if it is within the room temperature range. When the engine is cold, the gauge will register at the bottom of the coolant temperature operating range. In most cars, at the cold reading is 122 degrees Fahrenheit.
As you drive the engine becomes heated. The heat is transferred to the coolant and the temperature remains regulated. Once the engine is warm and everything is functioning correctly, the engine temperature will read at either between 180 and 220 degrees Fahrenheit.
This temperature reading should stay solid in that neighborhood until you shut the vehicle off. When you stop the vehicle, the coolant stops circulating, which decreases the temperature back down.n.