Last Updated: 30.03.2022

It’s a good day to be driving. The sun’s up, music’s blasting, and you are having fun in your car. All of a sudden, the temperature gauge fluctuates. Now you’re worried and start thinking about what is wrong. 

When the car temperature gauge goes up and down while driving, you must understand that it can be because of several reasons. Aside from the cause, know the fixes. Read on as we talk about the root of the problem, as well as the best solutions. 

Reasons Why Car Temperature Gauge Goes Up and Down While Driving

car temperature gauge on dashboard

As soon as you see a steep rise and fall in the temperature gauge, you might panic. Especially if you are a new driver, such a situation can be worrisome. It can be because of several problems, including the following: 

Stuck Thermostat 

The thermostat is one of the most important components of your car’s cooling system. It has an antifreeze or liquid coolant, which is responsible for preventing the engine from overheating. In a conventional design, the thermostat has a two-way valve that opens and closes at a specific temperature. Hence, when there is a problem, the temperature gauge fluctuates. 

One of the most common problems in a thermostat is that it gets stuck. When it stays open, the coolant continuously flows into the radiator. As a result, the engine runs cold. It will have a higher emission and will increase fuel consumption. 

On the other hand, when the thermostat is stuck in a closed position, a blockage exists in the circulation system. It prevents the cooling of the radiator, resulting in overheating. 

When the thermostat is stuck in either an open or closed position, the temperature changes. Often, it is because there is a broken thermostat valve, so such might need repair or replacement. 

Blown Head Gasket

blown head gasket picture

Sitting between the engine block and cylinder head, the head gasket is a small but crucial component that facilitates internal combustion. It lets the oil and coolant travel in the engine. More so, it lubricates different parts to minimize wear. Over time, it can suffer from significant damage, and one of the consequences includes fluctuations in the temperature gauge. 

When the engine overheats, the temperature increases at a dangerously high level, which causes the head gasket to blow. It warps and causes the coolant and oil to mix. In turn, it creates sediments that can clog the system. This will prevent the flow of the coolant, which will make the temperature irregular. 

As soon as the head gasket blows, act immediately. If you continue to operate the vehicle, other problems will be apparent aside from the fluctuations in the temperature gauge. Your inaction will let pressure escape from the engine, which can compromise its performance. 

Cooling System Problems 

A faulty cooling system is another common culprit when the temperature gauge in your car rises and falls as you drive. It means that some of the components under the hood are not working properly. This is especially the case if the problem persists despite the engine not overheating. 

Your car’s cooling system has different components that are prone to clogging over time. These clogs will prevent the various parts from delivering optimal functionality. Some of the parts that can be damaged include the radiator hose, water pump, and heater core. Rust, sediments, and debris can clog them, which will cause the temperature to fluctuate. 

More so, it is also possible that air cannot escape the engine’s cooling system. This will act as a blockage, which will prevent the normal passage. As a result, it can significantly increase or decrease the temperature.

Water Pump Damage

man holding a damaged car water pump

Speaking of the cooling system, one of its crucial components is the water pump. The main function of the water pump is to drive the coolant to the cooling system. If it isn’t working properly, then there can be recirculation problems, resulting in an increase in temperature. The engine will overheat. 

Pay attention to the tell-tale signs that the water pump is failing. One of the most common is a coolant leak, which is most evident on the middle portion in front of the car. You should also inspect the water pump and watch out for signs of wear, including rust and corrosion. Another common symptom is steam from the radiator. 

Overheated Engine 

When the engine overheats, it is also possible that the car temperature gauge will move up and down when you are driving. This can be a combination of the different problems that are listed in this article. To add, it can also be because of an inferior battery and harsh environmental conditions that your vehicle cannot handle. 

Even if many of today’s modern engines are built to be highly capable, they aren’t invincible. If it overheats, your car may stop out of nowhere and you can be in trouble when it won’t start anymore. Plus, it can also speed up damage to the various components, such as seals, hoses, and gaskets. 

Faulty Electronic Control Unit

car electronic control unit

The primary function of an electronic control unit or ECU is to direct the electronic features of a vehicle. It has numerous applications, including brake control fuel injection, and optimizing suspension. At the same time, it is also responsible for maintaining the right temperature, hence, as soon as the ECU is problematic, expect fluctuations in the temperature gauge. 

When the ECU has problems, it won’t recognize the real-time temperature. Hence, it might have false or fluctuating readings. Aside from the ECU, the coolant temperature sensor can also result in the same problem. 

Broken Radiator 

A car’s radiator is a heat exchanger, which is a crucial component of the cooling system. It eliminates excess heat, ensuring the optimal functionality of the engine. At the same time, keeping the system cool lessens the wear on the engine components. As soon as the radiator breaks, several problems can emanate, including movements in the temperature gauge. 

Changing the radiator maintains its peak performance. Otherwise, the coolant’s color will change and become rusty. Aside from the discoloration, it also makes the engine inefficient. Plus, it can be prone to rust over time, which will minimize its functionality. 

Bad Radiator Fan

bad radiator fan

While there are many radiator issues that can cause the temperature gauge to fluctuate, one of the most common is a damaged radiator fan. The main function of the latter is to blow cool air to the radiator to prevent it from overheating. 

Over time, the radiator fan becomes lousy. Dirt and debris will accumulate on the surface. Rust and corrosion can also be apparent, among other superficial damages. These can result in erratic functionality. As it fails to work as necessary, there can be significant fluctuations that affect the reading on the temperature gauge. 

Lack of Coolant Liquid 

Also called antifreeze, the car coolant prevents engine overheating. It also has lubrication benefits to minimize wear on the moving parts. This is crucial for ensuring the smooth functioning of the components of the cooling system, which include a water pump, radiator, radiator hose, radiator fan, and thermostat control. It will be good to have a good idea of how much coolant should be in the reservoir

Once the coolant is low, the temperature gauge can drop. At the same time, it can also fluctuate. Pay attention to some of the most common signs that your car has a low coolant, including a blown head gasket, faulty coolant level sensor, and malfunctioning air conditioning system.

You should also learn more about how antifreeze works and if engine coolant evaporates. 

Temperature Gauge Failure 

At the end of the day, the problem can be as simple as the temperature gauge itself. Everything might be working fine, but the gauge itself can be erratic. Even if the internal temperature is right but the gauge isn’t working as it should, fluctuations can be apparent. 

Look at several culprits when the temperature gauge is not working. It can be related to problems in the temperature sending unit, electrical circuit, and control circuit.

Aside from fluctuations, the reading can also be too high or too low compared to the normal temperature. 

The Best Solutions for Car Temperature Gauge Going Up and Down 

If the car temperature gauge moves up and down, below are some of the best fixes: 

Change the Thermostat Valve

As earlier talked about, one of the potential culprits is the thermostat valve. Over time, it is prone to wear, which will compromise its functionality. The failure to replace it accordingly can be a nightmare. Good thing, replacing such can be an easy DIY task using basic tools that you most probably already have. 

When changing the thermostat valve, turn off the engine and let it cool down for at least 15 minutes. Jack your car for a higher clearance. Take off the radiator cap and drain the fluid. At this point, you can now take the thermostat off. Test if it is still in good condition. If it is damaged, it must be replaced.

Replace the Coolant Temperature Sensor 

Aside from the thermostat valve, the coolant temperature sensor is another component that can cause significant movement in the temperature gauge. It can also result in more serious problems, such as engine knocking.

The cost of replacing a coolant temperature sensor can range from $150 to $200, depending on the quality of the replacement and labor.

You can cut the cost by doing the job yourself. It requires basic wiring knowledge and familiarization with the engine components to complete the task. It will take only a few minutes of your time. 

Fill the Coolant 

As a part of your preventive maintenance, check the coolant, making sure that it is at the right level. Otherwise, it can compromise the performance of the engine and cause the temperature gauge to fluctuate. Aside from ensuring the right level, using a high-quality product is also a must. 

To fill the coolant, start by letting the engine cool down before you start the work. Look for the coolant reservoir and check the minimum and maximum lines. If it is below the minimum line, top it up with your choice of coolant. You can also choose to pre-mix 30% distilled water and 70% antifreeze. 

Maintain Your Car’s Cooling System 

Proper care and maintenance of the cooling system is most important in preventing the car temperature gauge from moving up and down while driving. Here are some of the top things to do: 

  • Flush the radiator and cooling system depending on the recommendations of the manufacturer. In most instances, you should do this after every 30,000 miles. This is important to prevent the build-up of dirt and debris.
  • Ensure the right mixture of the coolant replacement. Otherwise, it can do more harm than good, such as speeding up rust and corrosion. Check the container for the right ratio. 
  • Let the engine cool down before adding any liquid to the cooling system, especially coolant. Otherwise, it is not only scalding hot, but it can also exert unnecessary strain on the components. In turn, it can speed up the damage. 


How does a car temperature gauge work? 

The modern temperature gauges are electric, which has a scale on the face. It has a bimetallic assembly with two fastened metals. It needs an electric circuit for temperature reading. It also has a sending unit, which is what sends the temperature to the gauge. When the sending unit fails, the temperature reading will be inaccurate. 

Is it normal for a car temperature gauge to fluctuate while driving? 

It is not normal for the car temperature gauge to go up and down when you are driving. If it moves, then this is a sign that there is a problem. Check under the hood and pay attention to potential issues before it worsens. 

What is a car’s normal temperature? 

In most cars, the normal temperature should range from 195 to 200 degrees Fahrenheit. In most dashboards, however, you won’t see the exact temperature. Instead, you will see H and C markings, which stand for hot and cold. 

What should you do if your car temperature is too high or too low? 

As soon as the car temperature gauge fluctuates, pull over and reach out under the hood. Look at the cooling system and the surrounding components to see if there is any damage. Otherwise, you might suffer from worse problems, such as overheating. If you cannot diagnose the problem by yourself, go to a mechanic to fix the issue. 


If the car temperature gauge goes up and down while driving, you can assume that there is a problem with the cooling system. It can be because of various issues, such as a stuck thermostat, blown head gasket, damaged water pump, broken radiator fan, and low coolant fluid.