Why Does Car Temperature Gauge Go Up and Down While Driving? [See 8 Reasons + More]

You may be asking, “Why does car temperature gauge go up and down while driving?” Well, it happens due to several reasons. Drivers on the road keep their eyes on the temperature gauge. A simple task yet not without advantages.

Keeping your eyes on the temperature gauge gives you the chance to spot when there may be a fault somewhere in your vehicle that affects the engine’s operation; like when you notice that your car’s temperature gauge goes up and down as you drive.

Normally, the temperature gauge goes up as the engine becomes hotter, and keeps on rising when the engine is under a lot of strain like going uphill. Once the strain on the engine is relaxed, the car cools down, giving rise to a normal car temperature gauge as it returns to its operating temperature. 

How does a car temperature gauge work?

The car temperature gauge is a device that’s built into a car to monitor its temperature. The car temperature gauge tells what’s going on in the engine so you don’t drive and suddenly see smoke coming out of your car’s bonnet. It’s expected that any vehicle operates within the normal car temperature range, but sometimes it fluctuates. 

The temperature gauge in any vehicle uses a sensor designed to work with the thermostat to transmit an electrical signal through the vehicle’s ECU, which goes in line with the coolant temperature at the time. The sensor in question is called a thermistor. This suggests that it’s associated with the car’s thermostat.

What Causes Car Temperature Gauge to Go Up and Down while Driving?

Is it normal for a car temperature gauge to fluctuate? The answer is no. So, what causes car temperature to fluctuate? Well, there are several factors responsible for the fluctuation of a car’s temperature gauge. 

In a normal circumstance, the gauge hits the ‘red’ spot when the car is overheating. But if it reaches the red spot when the car is not overheating or the gauge rises when you stop the car then it means that something is not right. 

Let’s begin to look at what causes a car temperature gauge to fluctuate.

Engine Overheating

A vehicle’s engine becomes overheated once the temperature rises above 230°F. Beyond the temperature of 240°F to 245°F, severe damage is likely to occur. 

Overheating can cause your car’s engine not to start as the high temperature can make the cylinder head get out of shape and ultimately reduce the pressure the engine needs to start.

Engine overheating can make a car temperature to fluctuate.

Faulty Thermostat

A car thermostat regulates the temperature of the engine by the use of coolant. The thermostat, like regular car components, also has a tendency to develop faults over time. And when this happens, it can become stuck and unable to move. It could stay open, closed, or halfway stuck.

A bad thermostat that stays open will continually let the coolant spread throughout the engine and this results in a drop in the car temperature, even when the car is not sitting idle. On the other hand, when it’s closed and unable to open the coolant is stopped from flowing to the radiator to cool off the engine, hence, causing a rise in the car temperature. This also means the engine experiences overheating. 

Finally, in the situation where it is halfway stuck, it requires more time than usual to get the engine to warm up because it’s half-open and allows some coolant to flow continuously to the engine.

Faulty Cooling System

The purpose of the cooling system is to maintain a consistent temperature in the car engine. The engine’s temperature should not be rising so high or dropping too low. The cooling system is made up of several parts.

A faulty cooling system as a result of a failing component within the cooling system can result in the car temperature fluctuating. Such components could be a bad thermostat, a bad radiator, failed radiator fan, bad water pump, or low-level coolant.

If any of the components making up the cooling system fails, the engine will not be cooled properly leading to overheating and temperature rise.

Low Coolant Level

A low coolant level can lead to overheating. This should be checked by drivers from time to time to ensure the coolant level is not below the allowable level. 

Even in cases where there is leakage overheating is likely to occur to the engine stating clearly a rise in temperature. A discolored coolant may also be a cause of a rising temperature in a car because in that state it becomes less efficient in cooling the engine.

Bad Radiator Fan

A radiator fan is made to cool the radiator which receives the coolant for the engine. It is fixed close to the reservoir tank. A sign of a bad radiator fan is engine overheating while the car is idle. 

While driving, you have the winds blowing, which keep the engine cool. So, if you notice overheating in the engine once the car is brought to a halt, it is most likely the fault of radiator fans which are meant to draw in sufficient air to cool the engine after driving.

Bad Radiator

A clogged, leaking, or rusty radiator can cause a car’s temperature to rise.

 Water Pump Issues

A bad water pump is one of the reasons an engine’s temperature can rise abnormally. When it breaks or has a leakage, it is unable to cool the engine properly because it serves to take the coolant (from the radiator) and circulate it around the engine to keep it cool.

Bad Head Gasket

A driver can check on his head gasket to see if it’s defective when his car temperature gauge rises and falls. This is one of the most possible causes. It’s placed between the cylinder head and the engine block.

Its purpose is to make easy the circulation of coolant and oil throughout the engine for cooling and lubrication respectively. The car runs on an internal combustion engine, and the head gasket maintains this by sealing up the combustion process thereby preventing a mixture of oil and coolant in the combination chamber.

However, when it ceases to work properly the head gasket can become bent allowing coolant and engine oil mix to form an oily coolant. This mixture spreads around the engine and the radiator leading to a clustered passageway for coolant due to the formation of sediments.

Symptoms of a blown head gasket include white smoke with a fine scent and dewdrops coming from the exhaust pipe, foam or bubbles in the car’s oil, and low coolant level.

Why Your Car Temperature Gauge Will Go Up and Down When Idle

This refers to a car overheating at a halt or stop in traffic or when the engine is turned off. The cause could be a bad radiator or a low coolant level.

Fixing Your Car When Temperature Gauge Goes Up and Down

Changing A Bad Thermostat Valve

  • Lift the car and place a bucket underneath to collect the coolant as you remove the clamp. Then pull off the hose.
  • Proceed to remove the old thermostat. Make sure the new one is the right match for your car.
  • Put in the new thermostat. Then tighten up the necessary points.
  • Finally start the engine and confirm the thermostat is working well.

Replacing The Coolant Temperature Sensor

  • Place a bucket beneath the sensor. Unplug the connector and remove the old sensor. (Make sure the new one matches your car.
  • Replace the sensor. Reconnect and tighten where necessary.
  • You can also check the coolant levels. Then start the engine and confirm its efficiency.

Removing Air from the Cooling System

When air finds its way into a cooling system it forms air bubbles within the radiator causing a rise in car temperature with unstable readings from the thermostat.

Frequently Asked Questions

Is it normal for a car temperature gauge to fluctuate?

A car temperature gauge is made to last for a long time. At the moment you spot a fault move quickly to fix it without delay.

What does it mean when your temperature gauge goes up and down?

It simply means your engine is overheated.

What does it mean when your temperature gauge stays on cold?

Your temperature gauge on a normal condition stays on cold until your engine has run enough then it starts rising. If it continuously releases coolant to the engine, the engine becomes cool and can affect the car’s performance.

Bottom line

Fluctuation in your car temperature gauge is caused by several factors like a blown head gasket, faulty cooling system, bad radiator, etc. They are inexpensive to replace and require an immediate response when they begin to develop defects.



Why Does Car Temperature Gauge Go Up and Down While Driving?

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