Updated at: 02-08-2023 - By: Lucas

While driving, it’s important to keep an eye on the temperature gauge, especially if you’re stuck in heavy traffic or going uphill. There are a number of factors that influence how quickly the meter rises and falls as you drive. There are many things you can do to avoid your engine from overheating, including understanding how the temperature gauge works.

Temperatures rise as the engine warms up and climb even more when the engine is working hard, such as when driving uphill.. The engine will begin to cool down and return to its normal operating temperature once the stress has subsided.

How The Temperature Gauge Works

Car Temperature Gauge Goes Up And Down While Driving

The engine’s working conditions can be seen on the temperature gauge. A vehicle’s tachometer is second only to the speedometer in terms of importance.

In order to prevent engine damage, the gauge shows you how hot the coolant is running through the engine. The radiator and engine heat the coolant, which the water pump then circulates through the system.

If the airflow isn’t sufficient, the thermostat will turn on the radiator fan and keep the temperature where it should be. Sensors that measure the coolant temperature transmit an electrical signal to the thermostat, which is then used to calculate the gauge reading.

Understanding The Temperature Gauge Movement

It’s critical that you know what the normal range of movement of the temperature gauge is. When the engine is cold, the temperature gauge begins at the bottom since the lowest value is normally set at 122 degrees Fahrenheit.

The engine’s internal combustion generates a great deal of heat as soon as you start it up. The heat of the engine is exchanged with the coolant in an effort to equalize the temperature difference, according to the thermal principles of physics. As soon as the engine achieves a temperature of 180 to 220 degrees Fahrenheit, the temperature gauge will rise. The ideal temperature is plainly displayed on most car temperature gauges.

Coolant and internal combustion will end when you park the vehicle and turn off the ignition. It is easy to see a rapid drop in temperature because the sensor is close to the thermostat, which allows it to cool faster than the coolant trapped inside the engine.

When a vehicle is mechanically sound and operated to its full potential, the temperature gauge positions described below are what to expect. A variety of factors might cause fluctuations in the gauge, which will be discussed in the following sections.

How Does The Thermostat Work

As a valve between the engine and the radiator, the automobile thermostat is an exceedingly simple device. During hot weather, the thermostat expands to open the valve, and when it is cold, it contracts to keep coolant from circulating. Using synthetic wax, which is responsible for shrinking and expanding, this technology is fantastic.

Temperature Gauge Goes Up Too High

Car Temperature Gauge Goes Up And Down While Driving-2

In most cases, the temperature gauge will rise over the ideal operating temperature for one of two reasons. The first is that you’re driving uphill incorrectly, and the second is an issue with the coolant system.

Uphill Driving

The added strain on the engine occurs when traveling uphill. There’s an inclination to contend with as well as driving the wheels and propelling the car along. When you’re driving uphill, your engine goes through the identical motions that climbing a flight of stairs or riding a bike does.

My grandfather/driving instructor has taught me how to handle hills as one of the first lessons. Keep the automobile in a lower gear while using a manual transmission to raise the RPMs by about 3,000 RPM, which is about half the distance from zero to redline.

The same principle applies to automatic transmission cars, with the exception that changing into the 3, 2 or L positions is required to prevent the transmission from shifting up. An in-depth discussion of this topic can be found in our article titled. What Is the Gear Shift Letter L?

You don’t have to drive quickly just because you’re pushing the RPM; the gear ratio will prevent that. In order to keep the water pump from overheating, you need to increase the RPM. In addition, the engine has more power at higher RPMs, thus traveling uphill will be less of a challenge.

Lack of Coolant

Look under the hood for the coolant reservoir. You can tell it apart from other bottles by the steam warning label on the top. In addition, it contains coolant markers on the side and a minimum and maximum gauge. The antifreeze-smelling liquid will be blue, green, or red if it isn’t connected to water.

Open the cap and add more coolant if the level falls below the minimum. Colors of antifreeze should never be mixed, although brands can. It’s best to use demineralized or distilled water if you’re going to add water to the mix.

Whenever the coolant gets heated, it’s pressured and will burst out in a cloud of smoke and boiling hot liquid, which can cause significant burns. This is why the steam warning is there. Do not remove the coolant cap unless you are convinced that the engine has cooled enough to do so without risking serious injury. In this article, we spoke about how long you should wait for the engine to cool down.

When compared to antifreeze, water has a lower boiling point but a higher freezing point. A small amount of water can be safely used in a vehicle that runs between 180 and 220 degrees Fahrenheit before it overheats. It gets significantly worse in the winter. When water freezes, it expands, causing pipes to shatter, the water pump to break, and even the engine block to split.

As a result, a 50/50 solution of de-icing fluid and purified water is strongly suggested. A water-based coolant solution can be used on the road if you don’t have time to run an antifreeze tests before the winter.

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Failing Water Pump

The cooling system’s coolant is pumped around by the water pump. Having no way to circulate it away from the engine causes the coolant to rapidly heat up if it breaks down. Coolant leakage and whining noises from the pump are the initial warning indicators, but a more catastrophic breakdown may cause the temperature gauge to quickly rise.

Bad Radiator

It is the radiator’s job to keep the coolant cool enough to continue its journey through the engine. It’s important to inspect the radiator thoroughly before making a decision on whether or not to replace it or get it repaired. In our guide on how to flush a radiator, we go over every method of cleaning a radiator.

Temperature Gauge Won’t Go Up

The thermometer will take longer to reach its normal reading in the winter. If, on the other hand, it appears that the temperature will never rise to that level, there may be an issue with the thermostat. It’s possible that it’s broken and stuck open, allowing the coolant to circulate even when it hasn’t reached the desired temperature. The thermostat should be replaced as soon as possible since driving with an engine that is too cold might lead to further malfunctions and difficulties.

Temperature Gauge Goes Up and Down While Driving

Car Temperature Gauge Goes Up And Down While Driving-3

Despite the fact that it’s quite rare for the gauge to change while driving, it’s possible. There are four possible explanations for the fluctuation of the gauge:

Bad Thermostat

The coolant temperature should cause the thermostat to expand and shrink. Coolant will gradually reach the desired temperature if the thermostat is working properly.

The coolant’s temperature may fluctuate because the thermostat opens and closes the valve too quickly, even before it breaks completely. As a result, the coolant temperature is properly measured by a temperature gauge that fluctuates.

Malfunctioning Coolant Temperature Sensor

This sensor is also known as the engine coolant temperature sensor (CTS) or the coolant temperature sensor (CTS) (ECTS). With a temperature-dependent CTS resistance, it receives a controlled voltage from the electronic control unit (ECU). The temperature gauge receives its data about coolant temperature from the ECU via the resistance. The temperature gauge will fluctuate erratically if the CTS is malfunctioning.

Failing Temperature Gauge

It’s highly improbable that the thermometer is malfunctioning on its own. Either the ECU or the gauge may be to blame for the pendulum-like swaying of the gauge, but both are likely culprits.

Problems With The Electronic Control Unit

Before you even notice a spike on the temperature monitor, you’ll start experiencing issues with the ECU. It may even prohibit you from starting the car because it controls so many technical systems. This is a significant issue, and you’ll need to seek the advice of a specialist in order to fully diagnose and resolve it.

How to Replace a Bad Thermostat

With the cost of labor running up to $100, replacing a thermostat on your own is an excellent money-saving option.

A funnel with a filter, a bucket, a flathead screwdriver, and a hose clamp are usually all that you need.

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Steps to Replace The Thermostat

  • Find the thermostat housing. It can be near the engine or inside the bottom radiator hose. Use google to find the exact location for your vehicle.
  • Place a bucket underneath the thermostat, as releasing the clamp will cause some of the coolant to pour out.
  • Use the flathead screwdriver to loosen the clamp and pull the hose off.
  • With the thermostat housing exposed and the coolant drained, unscrew the old thermostat and compare it to the new one.
  • If they’re identical, screw the new one in place. Replace the old hose clamp just in case.
  • Put the hose back on the housing and tighten the clamp.
  • You may need some help with this step, as you need to strain the drained liquid and pour it back into the coolant bottle.
  • Check the coolant levels and add more if necessary.

An novice mechanic may easily complete the task, which takes around 10 to 15 minutes. Before you go behind the wheel, make one final check to see that the engine is running smoothly and the temperature is within the recommended range.

How to Replace a Bad Coolant Temperature Sensor

The coolant temperature sensor can be easily replaced by just unscrewing one bolt and inserting in the new one that it is provided with. When we get to the steps, you’ll see what I mean, but first, let’s look at the list of equipment you’ll need.

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Steps to Replace The Coolant Temperature Sensor

If you’re familiar with the tight quarters of the engine room, you can do this task in under two minutes with minimal spillage. You should still take your time because you can re-strain any coolant that you might lose.


Why does my car temperature go up when I accelerate?

If your temperature gauge rises even little when you apply the brakes, you should have your car inspected to determine what’s wrong. Simple acceleration should not produce a difference in temperature because coolant levels should remain normal even if you drive strongly.

Accelerating while the engine is still cold is the lone exception. When you accelerate, the engine loses efficiency as it tries to reach its ideal operating temperature. It’s best to wait until the engine reaches the ideal temperature before accelerating quickly.

Is it normal for coolant temp to fluctuate?

What is the sensitivity of the gauge and how often is it measured? A temperature gauge that displayed real-time data would be too distracting to look at while the coolant temperature is being adjusted.

Unless you’re going up a steep slope or there’s a problem with the radiator system, you won’t see much movement on most gauges at the ideal operating temperature.

What are the signs of a bad thermostat?

You’ll notice a variety of indicators.

There will be higher or lower than normal temperatures, leaky coolant, heater malfunction, and engine bay noises.


If your temperature gauge is constantly fluctuating, this is a bad sign and may be fixed for a low price. Here, I’ve outlined the most common causes of erratic readings on the temperature gauge, as well as how to rectify them. My recommendation is to check out the Vehicle Freak website and learn more about your vehicle!