Pro Auto Talk is reader-supported. When you purchase through one of our links we may earn an affiliate commission (at no extra cost to you).

Car Temperature Gauge Goes Up And Down While Driving. Why?

Last Updated on: April 10, 2024

It’s a good day to be driving! The sun’s out, music’s blasting, and you are having fun. Suddenly, you notice something is wrong. The car temperature gauge fluctuates. 

What’s happening? Is it still safe to continue driving? 

When the car temperature gauge goes up and down while driving, several culprits are worth looking at. Read on as we talk about some of the top reasons, and more importantly, the best solutions when a car temperature gauge rises and falls. 

How A Car Temperature Gauge Works 

A temp gauge measures the temperature of the coolant liquid in the car’s engine. It will let you know if the coolant is cold, normal, or hot. It relays information from the cooling system to the dashboard. 

In old cars, the gauge works manually. They have a thin metal called a Bourdon tube. It contains an easily vaporized liquid, which allows the tube to expand when it is warm. Since it is manual, it works even when the engine is off and will return to the rest position when the engine is cool. 

In more modern automobiles, it is an electric system. In the case of the latter, the gauge works as a voltmeter. While the scale itself reads the temperature, the instrument reads voltage. It requires an electric circuit, which sends information for the gauge to show.  

Problems and Solutions: Car Temperature Fluctuates While Driving

The ideal engine temperature is between 195 to 220 degrees. If you are experiencing temperature gauge issues, you have a reason to worry. Here is a quick look at some of the reasons and fixes. 

1. Closed Thermostat Valve 

Closed Thermostat Valve

The function of the thermostat valve is to regulate the coolant’s temperature before returning to cool the engine. When the thermostat fails, it gets stuck. It results in an overheated engine. In turn, the car’s temperature gauge will fluctuate. Leaking can also happen, which you can confirm by looking at the thermostat housing. 

If it is closed, the coolant liquid will not flow, which makes the car’s engine prone to overheating. On the other hand, if the car thermostat valve remains open, the temperature will drop below normal, resulting in abnormal readings. 

How to Fix 

The best solution to a bad thermostat is a replacement. While it can be a DIY task, for those who do not have the knowledge and tools, it is best to pay a pro. 

On average, having a thermostat replaced by a pro will cost anywhere from $200 to $300. The thermostat costs $20 to $80, depending on the brand or quality. 

2. Blown Head Gasket 


If your car’s temperature gauge fluctuates, another potential culprit is the head gasket. Found between the engine block and cylinder head, it is responsible for maintaining internal combustion. 

Unsure if you should blame the head gasket? Watch out for some symptoms that it is blown, which include engine overheating, loss of power, milky il contamination, and white smoke coming out of the exhaust. 

A blown head gasket requires immediate attention. Fluids might leak, affecting the other components of the engine bay. 

How to Fix 

Using a chemical sealant is one of the best fixes for head gasket damage. It will close the leaking part without the need to disassemble. 

If a sealant does not work, you have no option but to replace it. Nonetheless, it can be expensive, with the price reaching approximately $2,000. 

3. Faulty Radiator

Faulty Radiator

The radiator eliminates extreme heat in the car engine. The air passing through its fins will help regulate temperature. One of its components is the radiator fan, which pulls air. The coolant stops flowing when there are faulty radiator fans, resulting in a fluctuating temperature gauge. 

A bad radiator cap can also be the reason why the car temperature gauge goes up and down while driving. If the radiator cap is weak, it is unable to regulate the temperature of the engine coolant. 

More so, you can also blame the radiator hose. It transports the coolant liquid throughout the engine. Any crack or serious damage will prevent proper flow in the coolant system. 

How to Fix 

You do not need to replace the entire radiator. Examine individual parts, such as a bad radiator fan or the radiator hose. The radiator cap might also need tightening. Only those with problems will require a replacement. If there is any part you will remove or replace, make sure there is a bucket underneath the engine to prevent liquids from spilling. 

4. Coolant Issues 


The coolant is one of the most common problems when the car temperature gauge rises and falls. When it is below the recommended level, you can expect an overheated engine. Look at the steam warning and volume markings to ensure the right amount of coolant in the car’s engine. 

More so, it is also possible that there is a coolant leakage. It can be because of damage in the coolant reservoir. 

How to Fix 

The first thing to do is ensure enough coolant. Check the coolant level, and if it is below what is recommended, add the right coolant. 

Meanwhile, if you are dealing with coolant leaks, an uncommon but effective solution is to add eggs. The heat will cook the eggs, which will act as a temporary plug. However, this is only a temporary solution. 

5. Engine Overheating

Man opening hood of overheating car

An overheating engine is another reason for inconsistencies in the temperature gauge. The normal operating temperature of an engine should not go beyond 230 degrees. When the car engine begins overheating, act immediately. Otherwise, it might cause serious damage, which can also be costly to repair.

Some of the reasons why a car overheats include lack of coolant, broken water pump, thermostat failure, and radiator issues. Safe to say, it is a combination of the factors that we are talking about in this article. 

How to Fix 

If you are driving when you suspect an overheating engine, turn off the A/C and crank the heater. Find a safe spot to pull over. Let the car sit for a while so the engine can rest. Check the coolant, radiator, and other engine parts when a car overheats. Fix and replace any issue. 

6. Issues with the Coolant Temperature Sensor 

Coolant Temperature Sensor

Often located at the base of a radiator, the coolant temperature sensor relays information to the engine control unit, and this data is then displayed in the car’s temperature gauge. Any issue with this sensor can result in engine knocking, which can also be a headache for car owners to deal with. 

Over time, the coolant temperature sensor can be prone to damage and corrosion. These problems will result in inaccurate readings. If you are unsure if the coolant temperature sensor is the problem, you can confirm this by using an OBDII scanner. 

How to Fix 

Like other parts in your car’s cooling system responsible for temperature gauge fluctuations, a replacement is an easy fix for a problematic coolant temperature sensor. If you replace it through a DIY task, the sensor can cost $65 to $90. On the other hand, you can also pay a pro to do the job and expect to pay up to $200. 

7. Bad Computer Module 

Bad Computer Module

The computer module acts as the brain and is responsible for monitoring the different components, including a faulty cooling system. It collects information from the sensors and displays it on the dashboard. If the computer module has a problem, the gauge reading will be inaccurate. 

A certified scanner is necessary to determine if the problem is the computer module. Proper diagnostics is possible only with the right tool. 

How to Fix

To prevent the car temperature gauge from having faulty readings, a repair is necessary. You can do this by fixing the power supply. Updating software can also do the trick. In other cases, however, it is beyond repair, and hence, you have no option but to replace it.  

8. Broken Temperature Gauge 

Broken Temperature Gauge

It is also possible that the temperature gauge itself is the problem. You might not need to go under the car’s hood and inspect the cooling system. The issue is right in front of your eyes, and it is in the dashboard. 

A bad temperature gauge also affects the ability of the computer to program the right air-fuel mixture. If it is damaged, your car can experience increased fuel consumption and a shorter lifespan. 

How to Fix 

First, make sure that all connections are secure. Check the sensors as well and look for corrosion or any other sign of serious damage. A tester is also a must-have to ensure correct information. 

Frequently Asked Questions 

Why is my car’s temperature gauge going up but not overheating? 

If the engine does not overheat but the temp gauge is rising, then the issue can be with the cooling system. There may be a clog or damage in the radiator. A low coolant, water pump damage, and faulty thermostat can also be common culprits. 

Why does my temperature gauge go up when I accelerate? 

It is normal for the temp gauge to be higher when you are accelerating. According to the law of thermodynamics, when energy passes into a system, such as heat, the internal energy changes. When you accelerate, the engine exerts more effort, making it hotter. It temporarily increases the engine’s temperature. 

Is it normal for temp to fluctuate while driving? 

It is unusual for the temp to fluctuate when you are driving, but it is a possibility. In most cases, it is a problem with the engine cooling system. Specifically, some of the issues include faulty radiator, computer module, head gasket, thermoset valve, coolant, and sensors. It can even be that the temp gauge itself is broken. 


If the car temperature gauge goes up and down while driving, several culprits are worth looking at. It can be because of a stuck thermostat, blown head gasket, damaged radiator, lack of coolant, overheating of the engine, faulty coolant temperature sensor, bad computer module, and broken gauge. 

Are there other reasons you would like to add to this list? Any solution that you want to recommend? Leave a comment below and let us know. 

Leave a Comment

© 2024 Pro Auto Talk - All Rights Reserved is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.