Why Car Temperature Gauge Goes Up And Down While Driving

There are affiliate links on this article. If you make a purchase through any of the links, I may earn a small commission at no extra cost to you.

As a driver, you may have wondered why car temperature gauge goes up and down while driving. It becomes more of a concern when the gauge goes up, yet, the car is not overheating.

There are also situations when the gauge goes up while the car is idle and not being used. All these are enough to get you worried about the health state of your car.

In this article, we will explain quite a lot of things that cause the temperature gauge to rise and fall inconsistently. Your radiator or temperature gauge may be bad, which is the reason for the issues you’re experiencing. But then, let’s discuss in details.

Why Car Temperature Gauge Goes Up And Down While Driving

The temperature gauge is only expected to rise to the “red” zone when the car is overheating. If the gauge rises to the red zone and your car is not overheating, it implies that something is wrong. Also, if the gauge rises when you stop the car, it also means that something is not right.

However, you should know that cars can overheat while sitting idle, and this can be due to a faulty radiator fan or other possible factors. But, basically, the paramount reason why your car temperature goes up and down while driving is due to a fault. Where could the fault have occurred? Let’s see.

Why Car Temperature Gauge Goes Up And Down and No Heat

Why Car Temperature Gauge Goes Up When Idle

Consider these factors are the major reasons for this issue.

1. Bad Thermostat Valve

Virtually all components that make up a vehicle can go bad and breakdown. This could be due to constant severe temperature, irregular maintenance practice(s), or accidents/collisions. Well, the thermostat may not suffer from either of these situations, but it’s still liable to get bad over time.

When the thermostat goes bad, it either stays permanently open, closed, or stuck halfway. However, regardless of how it got bad, the situation it stirs up is the same, which is, the engine will surely overheat while you drive.

Apparently, when the engine begins to overheat, the temperature gauge will rise. But, when the thermostat is malfunctioning (maybe it’s opening or closing when not supposed), then your temperature gauge will go up and down as you drive.

2. Faulty Cooling System

Another common factor why temperature gauge goes up and down, and no heat is the cooling system. As the name implies, this is the system that tries to moderate your car’s temperature. The cooling system isn’t one of the intricate systems in a car, but it is one of the most important.

If your car’s coolant reservoir is filled and yet this is happening, it may signify a faulty cooling system. In this case, you will need to check for clogged and/or damaged components that make up the system. You may not be able to detect these components; hence, you should call on a mechanic.

Why Car Temperature Gauge Goes Up When Idle

If you notice that your car overheats while in stop and go traffic or sitting idle, these factors listed below could be the cause.

3. Radiator Issues

Now, the radiator is one of the core components in a car that help to regulate temperature. It comprises fans and other components. The main function of a car radiator is to circulate air within the engine bay to cool it down and prevent overheating.

However, when you notice that your car temperature always go up when the car is idle, it could be a result of faulty radiator fans.

Naturally, when you’re driving, air would find its way into the engine bay and keep it cool; hence, your car’s temperature gauge will remain at the green/normal side.

Then, when you stop the car, and sufficient air isn’t forced into the engine bay anymore, then the engine may start to overheat, which can cause the temperature gauge to rise. Now, this may continue as you keep driving and meeting stops or traffic; thus, causing the temperature gauge to rise and fall continually.

That said, the reason why your car temperature gauge goes up when the car is idle can be linked to faulty radiator fans or the entire radiator components. To check the radiator fans, as a way of troubleshooting the problem, follow the guide below.

  • Find a safe place to pull over and turn off the car completely.
  • Wait for a while (for the car to cool down if you’ve driven for long miles) before touching the bonnet to avoid burning your palm.
  • Open the bonnet and check your coolant level – fill it up if necessary.
  • While the bonnet is still opened up, put the car in the ignition and return to check the radiator fan.

If the radiator fan is spinning, it is working fine; else, that was the culprit, or rather, one of the culprits. But you have to be careful, leaving a car in the ignition for too long can affect the engine negatively. Radiator failure should not be handled by just anybody; you should have a certified/trusted mechanic to fix it up.

4. Coolant Issues

Yes, the coolant can cause this problem to occur. When the coolant liquid is below the recommended level, it could lead to overheating. Also, if the coolant is leaking, overheating can happen, too. So, the coolant can cause your car’s temperature gauge to rise.

You should understand when you’re driving, even if your car’s cooling system is bad, your car would likely not overheat because a massive amount of air is being forced into the engine bay as you speed. But, the moment the car becomes idle after a long ride, it relies on some of its components/system to stay cool.

This is the moment where your car’s coolant, thermostat, and radiator comes into play. If any of these systems don’t respond while your car is idle, the engine’s temperature can go very high, causing the temperature gauge to shift from the normal zone to the “red” zone.

Note: When the gauge fluctuates (going up and down as you drive), that’s possibly not a coolant issue. However, it still calls for a check on the coolant and its components (hoses).

Always top up coolant liquid or antifreeze before driving out the car. Also, you should always check out for coolant leaks and fix them.

Read Also: How Far Can You Drive an Overheating Car?

Why Car Temperature Gauge Rises Then Falls

Why Car Temperature Gauge Goes Up And Down and No Heat

Everything mentioned so far can all contribute to the malfunctioning of your car temperature gauge. However, the temperature gauge itself can also get faulty and begin to malfunction. But, it is important to know that the temperature gauge works in different ways in different vehicles.

The temperature gauge can read incoherently if the coolant temperature sensor (CTS) is bad. There are other things that can cause the temperature gauge to malfunction, and could be the reason for the issues you’re facing.


The main reason why car temperature gauge goes up and down while driving is because something is not working properly in your car’s cooling system. It could be the radiator fan, water pump, thermostat valve, coolant, or the gauge itself.

To fix either of these issues, we’d advise that you engage a proven auto mechanic. Also, ensure that you stick to a maintenance routine and always be proactive regarding issues with your car.

Scroll to Top