Car Temperature Gauge Goes up and Down While Driving

Car temperature gauge goes up and down while driving means your engine is overheated and needs a quick fix. The common causes of the fluctuations are a low coolant level, a bad radiator, a faulty temperature sensor, a faulty thermostat, a broken water pump, and a blown head gasket.

Car Temperature Gauge Goes up and Down While Driving

The fluctuating gauge means that the cooling system is not functioning properly. Read on to discover how you can diagnose and fix these issues.

Why Car Temperature Gauge Goes up and Down While Driving?

A car temperature gauge goes up and down because the engine’s coolant temperature is high. The common causes of a fluctuating temperature gauge are a faulty cooling system, a low coolant level, a bad thermostat, and a defective temperature sensor. A quick fix is necessary to save the engine.


A car temperature gauge measures the temperatures of the engine’s coolant. The temperature gauge reading informs you if the coolant’s temperature is normal, cold, or overheating. When your vehicle is functioning normally, the temp gauge will rise after driving for a distance. However, if the temperature gauge fluctuates, you must check your vehicle for the following issues.

– Overheating Engine 

The standard engine temperature range depends on your car model. For most modern cars, the normal range is between 190 and 220 degrees. If the temperature rises above 230 degrees, your engine is overheating. The vehicle requires immediate attention if the gauge increases to 250 degrees or more. 

An overheated engine is hard to start, especially when the high temperature warps the cylinder head. The result is weak pressure that the engine requires to start your car. If you do not fix the issues immediately, the pistons wield into the cylinder. You will need an engine overhaul when that happens. Hence, it is advisable to visit the nearest mechanic immediately to replace any faulty part to save the engine.

– Low Coolant Reservoir

A low or diminished coolant level causes the car engine to overheat, leading to a fluctuating temperature gauge. Modern car models have reservoir tanks with visible markings that allow you to determine the engine coolant level at a glance. The level may diminish if the reservoir leaks for a long time.

Check the marking regularly to determine if the car has any leakages. Let the mechanic identify and fix the faulty part of the temperate control unit to maintain an average coolant level in case of a leakage. The temperature gauge will fluctuate if you keep driving with a low coolant level. Eventually, the engine may fail due to overheating.

– Blown Head Gasket

The head gasket is located between the engine block and the cylinder head. The function of the head gasket is to seal the engine’s combustion chamber so that your car generates enough compression to maintain the engine’s power. In addition, the head gasket prevents the engine oil and coolant from leaking.

Why Car Temperature Gauge Goes up and Down While Driving

The engine gets optimal lubrication and cooling when the head gasket functions well. However, the head gasket is warped if the engine overheats due to coolant leakages or other issues. The engine oil and coolant mix. The oil in the coolant may form deposits or clogs in the passageway as the mixture flows through the engine.

The oil clogs prevent the coolant from flowing freely into the engine, which raises the engine temperature further. If you continue to use your car with a blown head gasket, the temperature gauge fluctuates because of the interruptions in the coolant flow. 

Driving with a faulty head gasket is risky because of the overheated engine. It is advisable to fix it immediately. Common signs of a blown head gasket include a constantly overheating engine or the fluctuating temperature gauge, white smoke from the tailpipe, and diminishing coolant without leakages.

– Faulty Water Pump

The water pump is a part of the car’s cooling system. It suctions the coolant from the radiator into the engine block and cylinder head before it flows back into the radiator. The process is inefficient when the water pump fails or wears out. A faulty water pump cannot propel the coolant to the engine. The car overheats until the pump is repaired or replaced.

When the water pump is faulty, other parts of the cooling system, including the head gasket and cylinder head, may be damaged. However, before you replace the water pump or blame it for the fluctuating temperature gauge, ensure that all other parts of the cooling system are functioning correctly. Check the condition of the radiator, thermostat, coolant reservoir, and radiator hoses.

– A Bad Radiator

A radiator regulates the coolant’s temperature. The coolant flows back into your car’s radiator after cooling off the engine. A faulty radiator changes the color of the coolant and fails to regulate its temperature. Consequently, the coolant’s temperature remains high, so it cannot cool the engine effectively.

The car temperature gauge will oscillate from standard to high because the coolant and engine are hot. In addition, when the radiator fan is faulty, sludge forms in the radiator. The sludge gives the coolant a rusty color, reducing its efficiency in cooling down the engine.

Check the radiator cap if your car’s temperature gauge fluctuates when idling. If the lid is not tightly sealed, air flows into the radiator and forms pockets in the hoses and heater core. The air pockets cause an irregular coolant temperature, which causes the engine to overheat. 

You can tell your car’s radiator cap is faulty or leaking if the coolant is leaking. The coolant reservoir may overflow, or the radiator pipe may collapse if the cap is not replaced on time. Be sure to fix your car before such extreme outcomes because the repairs will be expensive.

– Stuck-closed Thermostat 

The thermostat regulates the engine’s temperature by controlling the flow of coolant. Depending on the engine’s temperature, the thermostat is either open or closed. When the thermostat is open, the coolant flows through the valve, reducing the engine’s temperature.

Car Stuck Closed Thermostat

If the thermostat valve closes, the coolant cannot flow to the engine, allowing it to warm to an average temperature. If the coolant overheats, it flows back to the radiator, which cools it down. A closed or stuck thermostat interrupts the flow of coolant to the engine as needed.

The most common problem with the thermostat valve is that it becomes stuck in either the closed or the open position. Consequently, the engine becomes too hot or cold. If it is stuck in the closed position, fresh coolant cannot flow into the engine to cool it down. Your car temperature gauge fluctuates because of the overheating engine.

If the thermostat is partially stuck, the coolant keeps flowing into the engine even when the engine is not overheating. You will notice that the temperature gauge goes down instead of going up as you drive. The partially stuck position is less harmful to your car than an overheating engine. However, it will increase your fuel consumption significantly.

– Broken Temperature Gauge

The coolant temperature sensor (CTS) may fluctuate if faulty or damaged. Your car experiences engine knocking and other mechanical issues. Engine knocking means that the fuel in the engine cylinder burns unevenly. The irregularities in burning fuel produce noises and shocks because of pre-ignition.

How To Fix a Fluctuating Car Temperature Gauge

To fix a fluctuating car temperature gauge, determine the underlying cause first. Start by checking for leakages that reduce the coolant level and then inspect other components, such as the temperature sensor and thermostat.


Add the coolant if the level is low, and then test the temperature gauge. Inspect other components if the fluctuations persist. Regular service will help you identify and fix any faulty parts quickly.

– Check and Fix Coolant Leakages 

A low coolant level causes the temperature gauge to fluctuate because of the engine’s high temperature. The measure of coolant in the reservoir may be visible depending on your car model. If the indicator shows a low level, switch off the engine and allow the car to cool for 20-30 minutes. Top up the coolant to the recommended maximum level for your vehicle.

Remedies of Fluctuating Car Temperature Gauge

Leakages cause the coolant to diminish fast. If the temperature gauge shoots from regular to high after topping the coolant up, check for leakages and ask your mechanic to check the source. The mechanic may advise you to buy new parts to fix the leakages, which will increase the cost of the repairs.

– Replace the Faulty Parts of the Cooling System

When the temperature gauge goes up and down, diagnose all the cooling system parts. Tightening or replacing the radiator cap can prevent air from penetrating the engine and forming pockets that destabilize the engine temperature. If the radiator is rusty, consider replacing it with an aluminum radiator, which is less susceptible to rust. 

Your mechanic can help you to replace or fix a faulty water pump or head gasket. It is easier to diagnose all the issues with the cooling system at home if you are a professional mechanic. If filling the coolant reservoir does not solve the fluctuations, go to a mechanic for a complete cooling system diagnosis. You may need to replace more than one part to fix the problem.

– Replace the Coolant Temperature Sensor

You can replace the faulty coolant temperature sensor at home to avoid engine knocking and false alarms on your temperature gauge. You will require a good OBD2 scanner to determine if the sensor is in good condition. If the scanner shows that the sensor is faulty, switch off the engine and jack the car’s front side as you allow it to cool down for 20 minutes.

Open the radiator’s cap to drain the coolant and disconnect the sensor’s wiring connector. Disconnect and replace the faulty coolant temperature sensor and reconnect the wiring connector. Switch on the engine to confirm that the temperature gauge is working normally. If you need clarification on the replacement process, allow a qualified mechanic to replace the faulty sensor.

– Replace the Faulty Thermostat

You can replace a faulty thermostat valve alone or with the help of a mechanic. However, you need the right tools, including a hammer, vise grips, screwdrivers, an OBDII scanner, an adjustable wrench, a pocket knife, and a screw jack.

Here is the process of replacing a faulty thermostat:

  1. Switch off the engine and leave the vehicle to cool down for 20 minutes
  2. Jack up your car for safety
  3. Open the radiator’s cap and drain the radiator
  4. Detach the thermostat valve. The valve is at the top or bottom of the radiator, depending on the car model
  5. Check if the thermostat valve is functioning properly by dipping it in a basin of hot water. If it remains closed, the thermostat is faulty.
  6. Ensure that the coolant plugs are in place, then install a new thermostat
  7. Start the engine to confirm if the fluctuations of the temperature gauge have reduced or stopped

Further diagnosis is necessary if the fluctuations continue after replacing the defective thermostat. In addition, only attempt to replace the thermostat valve with the right tools and procedure to avoid additional complications. Seek professional help if you feel unsure about the replacement process. 

– Service Your Car Regularly

Regular service saves you high repair costs because your mechanic can detect issues before they escalate. The faulty part may be beyond repair when your car temperature gauge goes up and down. Be sure to attend all scheduled services and report minor signs such as leakage or smoke in your tailpipe. 

Drive or tow your vehicle to a qualified mechanic immediately after the temperature gauge starts fluctuating. Your choice of a mechanic or repair company is critical. Ensure that the company has qualified mechanics to handle your car model. In addition, ensure that the mechanic replaces faulty parts with top-quality parts with long service life.

Solving Car Temperature Gauge Goes up and Down


You have nothing to worry about when your car temperature gauge goes up and down while driving because you know the causes. You have also learned how to fix the issue at home or with your mechanic.

Here now is a summary of the main lessons you have learned in this article:

  • The car temperature gauge fluctuates when the engine is overheating.
  • The engine requires a high coolant level and low coolant temperature for optimal performance.
  • Faulty parts of the cooling system, including the radiator, head gasket, water pump, and thermostat, cause fluctuations.
  • A broken coolant temperature sensor can also cause the gauge to fluctuate.
  • Replacing the defective part(s) of the cooling system fixes the car temperature gauge fluctuations.

You can use the information you have obtained from this article to save your engine from the damages associated with prolonged overheating.

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