Car Temperature Gauge Goes Up And Down While Driving – Is It Why?

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As a careful driver or car owner, your eyes have to constantly be on the temperature gauge when driving.

When you notice that the temperature gauge goes up and down, you should take action. But, don’t panic. Rather, you should pull over and find out why the temperature gauge fluctuates.

This may not be easy, especially when you’re in an unsafe place. You can continue driving until you get to a mechanic shop or a place safe to inspect what the cause could be.

A fluctuating movement of the temperature gauge is a sign that something is wrong and you shouldn’t gloss over it. It can either suddenly rise high or drop to the lowest point.

It can be when the engine is running. At other times, the gauge may rise and fall when the car is idling. While this is happening, the car may not overheat.

The question is, ‘why does the temperature gauge go up and down?” This article explains all you need to know about the causes of the inconsistent rise and fall of a car temperature gauge. I’ll also offer what you can do to fix it.

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

The first suspects when the temperature gauge goes up and down are a stuck-closed thermostat valve, blown head gasket, and a bad cooling system.

The problem can also be due to issues with the radiator, lack of coolant, uphill driving, and a failing water pump.

If there’s a faulty temperature gauge, malfunctioning electronic control unit (ECU), or a problem with the coolant temperature sensor, the temperature gauge can misbehave.

Each of these reasons manifests in different ways. The cause to attribute depends on the position of the gauge at the time.

The causes when the temperature gauge goes up too high are different from what causes the gauge to go up without overheating.

They also differ from what triggers the gauge to go up when the car engine is idling. If you notice that the gauge goes up from hot to normal, a faulty-sensitive thermostat is a suspect.

The truth is, it’s, literally speaking, a case of different strokes for different folks. But let me start by explaining the working mechanism of the temperature gauge.

How The Temperature Gauge Moves And Works     

Depending on your car design, the temperature gauge is usually located leftward of the speedometer and it’s an important component of the car.

If you’re driving a car that uses an internal combustion engine, you must pay close attention to the temperature gauge. The gauge is responsible for indicating the coolant level and how it runs in the engine.

While the water pump pushes the coolant towards the engine to heat up, the radiator, on the other hand, cools the engine. This is to ensure relative balance in heat generation.

The thermostat helps to regulate the amount of heat generated by triggering the radiator fan for proper airflow. The temperature gauge gets its reading from the coolant temperature sensor (CTS).

The CTS, located next to the thermostat, measures the amount of temperature received from the coolant and or thermostat.

It then sends the electrical signal to the on-board control system (OCS) where the gauge takes its reading. From there, you can keep track of how hot or cool is your engine.

The rise in the temperature gauge is not a sign that something is wrong or has gone bad with your engine.

In any case, the gauge starts to rise from zero as your car engine heats up. The rising won’t stop nor the gauge returns to zero until the strain or heat level on the engine has subsided.

The more the strain on the engine, the higher the gauge rises. The maximum running temperature of a vehicle is between 180 and 220 degrees Fahrenheit.

This is normal for every vehicle. But what’s the issue when the abnormal happens? Let’s find out.

Car Temperature Gauge Goes Up And Down While Driving: Causes And Fixes

The temperature gauge can move from normal to hot. This is the most abnormality you’ll find with the gauge on your dash. The sudden rise can be due to a few things.

Failed Thermostat

While the thermostat may not suffer from collision, severe temperature, or irregular maintenance issues, it can still go bad.

By design, the thermostat is supposed to contract and expand relative to the coolant temperature. However, when it goes bad, it may either remain indefinitely open or close.

Alternatively, it may open or close the valve too quickly or stuck halfway. It doesn’t matter whether the thermostat is open, close, or stuck. As you drive, the engine will start to overheat.

The result is a steady fluctuation in coolant temperature. Once the coolant temperature doesn’t settle, the temperature gauge will start to go up and down.

What To Do    

The thing to do once you notice that the thermostat is faulty is to replace it. It won’t take you more than 15 minutes to complete the thermostat replacement.

With $300, you can buy and install a good thermostat. Labor costs can be anywhere around $100.

Faulty Radiator

A faulty radiator causes the temperature gauge to go up when the car is idling. Needless to say, a failing radiator will cause your car engine to overheat.

It doesn’t matter whether you stop, stuck in traffic, or stay idle. The radiator distributes air and ensures airflow through the engine bay.

It houses the fan that cools the engine as you drive and it heats up. Essentially, the radiator is designed to prevent overheating.

What it implies is that a faulty radiator is the first suspect when you notice that your car temperature gauge rises when the engine is idling.

If you continue to drive and get stuck in traffic, the gauge will start to go up and down.

What To Do

As soon you notice that the temperature gauge of your car is rising, what you should do is to pull over and switch off the ignition. Allow the engine to cool for about 15 minutes or more.

It’s possible the coolant level has come down or the fan has stopped working. Fill the radiator up with coolant and check if the fan has stopped due to wiring disconnection.

Defective Cooling System         

It’s a no-brainer to suspect the defective cooling system for a rise and fall movement of your car’s temperature.

When the cooling system fails, the temperature gauge will rise and fall but the car engine will not overheat.

The coolant system houses the coolant, thermostat, water pump, and radiator. When any of this is faulty, then the temperature gauge is the victim.

For instance, a faulty water pump won’t pump coolant through the engine block and cylinder head to the engine.

As a result, the engine will overheat, the head gasket will warp, and a host of other internal components be damaged. The temperature gauge will start to increase suddenly.

What To Do

When the cooling system goes bad, it’s time to look into the various defective components and replace them.

Calling a professional mechanic will be the best bet. in the interim, you can fix some of the components that a simple DIY procedure can fix.

Blown Head Gasket

Another reason your car temperature gauge may fluctuate is when you have a blown head gasket.

The head gasket is located between the engine block and the cylinder head and primarily functions to ensure complete internal combustion.

It circulates oil and coolant that help in lubricating and cooling the engine. As a result of serious engine overheating, the head gasket can blow or become warped.

The consequence is the mixing of oil with coolant. The harmful oil-coolant mixture can clog the passageway of the coolant.

Once the coolant can’t reach its destination, the engine overheats and the temperature rises astronomically.

What To Do

There’s no other option to a blow or warped gasket than getting a replacement. Your car engine may not last long if you continue to drive it with a defective head gasket.

The white smoke coming from the car exhaust tailpipe is a clear sign that your head gasket is blown. Unusual coolant or oil leakage is also a sign.

Broken Coolant Temperature Sensor (CTS)

Another reason your temperature gauge may be fluctuating is when there’s a faulty coolant temperature sensor.

As earlier hinted, the CTS receives and sends a signal to the temperature gauge through the on-board control system.

However, once it’s failing, the gauge can no longer receive any signal.

Consequently, the gauge starts to move up and down as it can no longer read the temperature.

What To Do

You’ll need to test the health of the CTS using an OBD2 scanner. Once you can establish that the CTS isn’t working, allow your engine to cool for about 15 minutes.

Disconnect the wiring connection of the CTS and then drain the coolant in the radiator. Remove the faulty temperature sensor and replace it with a new one.

Replace the CTS wiring connector and ignite your engine to see if the gauge works. A new sensor can cost between $70 and $100 while labor costs can be around $100.

Final Thoughts

Like I said earlier, do not panic when the temperature gauge goes up and down. In any case, nothing gets resolved by worrying.

It’s either you find a solution to the problem squarely or park your car in the garage. I’m the latter won’t be the option.

Rise and fall in temperature gauge happen as a result of a faulty internal system.

The thermostat may be stuck or the water pump failed. If there’s a low coolant level or the gasket head is blown, the temperature gauge may suffer fluctuation fate.

In all, following the fixes I’ve explained above will resolve the issue and make the gauge start to function properly again.

I hope this article helps you with a DIY procedure of fixing a temperature gauge that goes up and down while driving.