Car Temperature Gauge Goes Up and Down While Driving – Main Causes

Have you experienced a situation wherein your car’s temperature gauge goes up and down while driving? If you are constantly experiencing it, you may have wondered if it should cause alarm. You may also wonder about the main causes why the car temperature gauge goes up and down while driving.

The typical reason your car’s temperature gauge fluctuates while driving is a problem with your cooling system. The cooling system has a lot of components. This means that it has multiple areas of concern that may cause the mentioned problem with the car temperature gauge. These include:

  1. A Malfunctioning Radiator Fan
  2. A Faulty Coolant or Water Pump
  3. A Blown Head Gasket
  4. A Closed Thermostat Valve
  5. Not Having Enough Coolant
  6. A Broken Temperature Gauge
  7. Issues With the ECU

These are only some of the many causes why a temperature gauge spike up and down. If you observed your car’s temperature gauge rising but not overheating, you must address this issue quickly. Addressing this concern immediately will prevent serious damage to your car’s engine.

Read on to learn more about why a car temperature gauge goes up and down while driving and their solutions.

Why Is Your Car Temperature Gauge Goes Up and Down While Driving

car temperature gauge goes up and down while driving

Let’s say you’re in the middle of an interstate trip when suddenly the temperature gauge spikes up. Should you be worried? Yes, you should but avoid panicking. There are more than a dozen causes of this problem. Fortunately, most of them are easy to fix even while in the middle of the road.

Here are some major causes of the temperature gauge going haywire to determine what you can do:

1. A Malfunctioning Radiator Fan

A Radiator Eliminates the Heat

The radiator utilizes the air passing through its fins to dissipate the heat collected by the coolant. The radiator fan makes it more efficient as it forces air through the fins. It does such function even if the vehicle is not running.

In some cars, the fan is essential because the radiator was downsized to fit into the bonnet. Without the fan, the radiator can’t cool the engine on its own. If the radiator fan malfunctions, the car temperature gauge goes hot than normal when the vehicle is not moving.

Causes of a Faulty Radiator Fan

  • Debris jamming the fan blades
  • Electrical issue/blown fuse
  • Broken fan blade
  • Shattered bearings

Any of these issues (and more) can stop the radiator fan from spinning. This makes it necessary to fix it as soon as you can.

2. A Faulty Coolant or Water Pump

Coolant Will Stop Flowing and Start Boiling

The engine coolant absorbs the heat from the engine and disperses it in the radiator. For the coolant to flow through the engine channels and the radiator, it will need a pump. If this pump fails, the coolant will stop flowing and start boiling.

Boiling Coolant Inside the Cooling Lines

Engine coolant has a much higher boiling point compared to water. However, note that it is still no match for the amount of heat a car engine produces. If the coolant stops flowing, it will boil inside the cooling lines. When that happens, the engine will overheat and seize.

Cooling Lines Might Rupture

Moreover, when the coolant evaporates and turns into steam, the excess pressure can rupture the coolant lines. Not only will your engine seize, but you will also have to deal with a severely damaged cooling system.

It is best to scrap the car and get another one if this happens. Note that this is only possible for people with lots of disposable income. For regular folks, this means taking the bus for a year.

Inspect the Pump for Damage

You can find the water pump just behind the fan belt. You can often find it bolted on the engine block. Once you locate the pump, you should inspect it closely for damage.

Signs of a Busted Water Pump

  • Rust/corrosion
  • Damaged bearings
  • Cavitation/pockmarks
  • Mineral deposits
  • Sludge buildup
  • Damaged/broken shaft
  • Leaking weep hole or on the mounting bracket

If you find any of these signs, you must have your water pump replaced immediately. If you don’t, you will find your car overheating every time you go out.

3. A Blown Head Gasket

Head Gasket Prevents Coolant Leakage

The head gasket seals the connection the cylinder head and the engine block have. This prevents the leakage of the following:

  • Combustion gases,
  • Lubricating oil, and
  • Coolant.

If your car’s head gasket fails, it can cause all sorts of problems, not the least of which is engine overheating.

A blown head gasket is dangerous because all the important fluids are leaking out. If left unattended, it can cause serious harm to your engine. Because there is no coolant and lubricant, it means serious damage like engine knock or damaged piston rings.

Signs of a Blown Head Gasket

  • Overheating – Because the coolant is leaking profusely, your engine will constantly be overheating.
  • Milky Oil Contamination – If you check the dipstick, you will discover that other fluids already contaminated the oil. This results in a milky residue coating the dipstick.
  • Loss of Power – The head gasket keeps the combustion cylinder sealed. This results in most, if not all, of the energy being contained and utilized. Without the gasket, nothing will keep all that inside the cylinders. This will prevent you from getting as much power from your engine as before.
  • White Smoke Out of the Exhaust – Since there is no barrier preventing coolant, oil, and fuel from mixing, your exhaust will be constantly spewing smoke. If the exhaust is just black, it means the oil combined with the fuel. If it is white, it is possible that the coolant mixed with the fuel.

You should take your car to the mechanic as soon as possible to prevent serious damage from happening.

4. A Closed Thermostat Valve

Monitors and Regulates the Coolant’s Temperature

The thermostat monitors and regulates the temperature of the coolant before it recirculates through the engine. Even though the thermostat is fairly simple and cheap to replace, it can cause several problems.

Effect of a Stuck Thermostat

If the thermostat is always closed, it will prevent the coolant from flowing. This will cause the engine to overheat. The car temperature gauge may also get hot then go back to normal.

Closed-circuit Cooling System

After 1980, almost all carmakers utilized a closed-circuit cooling system. It now includes a reservoir with visible markings to determine the coolant level. This promotes ease for car owners to monitor the coolant level. If there is even a minute drop in the coolant, you will need to top it up.

Effects of a Partially Stuck Open Thermostat

Meanwhile, having a partially stuck open thermostat will cause your temperature to go down while driving constantly. The reason is the constant circulation of the coolant through the engine. This might not seem like a problem, but it does bring its share of issues.

One problem you may experience is increased fuel consumption. Remember that the engine does not reach and retain its optimum working temperature.

This will result in it needing to burn more fuel to produce more power. So, whether your thermostat is stuck open or closed, you should replace it immediately.

5. Not Having Enough Coolant

Inspect the Coolant Reservoir

Open your car’s hood and check the coolant reservoir. The coolant reservoir is a white plastic container with a “steam warning” marking on the cap. Plus, the reservoir has volume markings (maximum and minimum) at the side.

If you don’t use water as a coolant, the liquid inside the reservoir will be blue, orange, green, or red. The coolant will also smell sweet.

Top Up When the Coolant Is Below the Minimum Level

If the coolant level is below the minimum level, take the cap and top up the amount. Note that you should never mix different colors of coolant. Use the same color coolant that is already in the reservoir. It does not matter what brand of coolant you use, provided it is the same color.

Also, do not top up the coolant reservoir when the engine is hot. The steam warning is on the cap for a reason. The coolant would be scalding hot.

It would also suddenly spurt out and cause serious burns. If your car does overheat, turn off the engine. Allow the coolant to cool down for five to ten minutes before topping it off.

Avoid Using Water as a Coolant

Avoid using water as a coolant. Water has a higher freezing point and a lower boiling point than proper coolant/antifreeze. Most vehicles have typical working temperatures between 180-220°F. This means they will easily boil water.

It gets even worse when winter comes because water expands when it freezes. It can, therefore, cause the pipes to burst and break the water pump. There is even a high chance for it to crack the engine block.

If you don’t have any other choice, use water. However, flush the cooling system as soon as possible and use proper coolant.

Again, the car temperature gauge goes up and down while driving- what causes this issue? The main reason why your car temperature gauge goes up and down while driving is due to a cooling system’s malfunctioning component. This part could be the car’s radiator hoses, thermostat valve, temperature gauge, or coolant.

6. A Broken Temperature Gauge

Another often overlooked cause behind the car temperature going up and down is the gauge itself. This might be obvious, but it is better to check out the other possible causes discussed earlier.

Corroded or Damaged Sensors

Corroded or damaged sensors can mess up the readings of your gauges, so you should check them, too. Also, ensure that all the connections are snug and no loose or cut wires.

Check the Connectors Using a Tester

If you have any electrical skills, grab a tester and check if the connectors are still good. If the temperature gauge and sensors are fine, there could be another cause for the spiking temperature.

7. Issues With The ECU

Monitors and Controls All the Aspects of the Car

The problem might also stem from the Electric Control Unit (ECU) or the car’s computer module. This part is essentially the brain of the car. It monitors and controls all the aspects of the car. If something is wrong with the ECU, this might explain the temperature problem.

Collects Information from the Engine’s Sensors

The ECU is responsible for collecting information from the sensors in the engine. It also controls them to prevent severe damage. It displays the information it gathers on the dashboard then alerts you when something is going wrong.

The problem here is that you can’t figure out this problem without a computer scanner. You have to take your car to a mechanic and have them scan the ECU to find the actual problem.

Effects of an Overheating Engine

what causes temperature gauge to drop while driving

You already know that engine overheating is a bad thing, but do you know exactly why it is so? Here are some of the reasons why you would not want your engine to overheat often:

1. Engine Knocking

One of the most dangerous effects of engine overheating is engine detonation, also called engine knock.

“Knocking” occurs when the air-fuel mixture in the cylinder erratically combusts in the cylinders. This can result in flame fronts colliding, meaning pistons that are supposed to be down are going up.

Engine knocking puts a lot of strain on your car’s engine. It can often destroy the pistons, piston rings, and rod bearings. Repairing engine knock is often expensive, and it is sometimes better to replace the whole engine.

2. Broken Seals and Gaskets

Engine seals and gaskets can withstand the heat and pressure from an engine’s normal operating temperature. However, both heat and pressure increase exponentially when the engine overheats. This will cause seals to melt, deform, or invariably fail.

3. Cracked Cylinder Head

The cylinder head expands and warps when exposed to extreme heat for too long, seeing as it is from metal. This is exactly what happens when the engine overheats.

Cylinder heads often use billet aluminum for their construction. This expands three times faster than iron, which is often the main material for engine blocks.

Since the cylinder head comes bolted onto the engine block, it cannot expand when needed. This means that the cylinder head will crack from the excessive pressure.

4. Head Gasket

Head gaskets provide a seal between the cylinder heads and block to prevent compression loss. They also seal oil and coolant passages to keep oil and coolant from mixing.

As mentioned above, really high temperatures can cause the cylinder heads to swell. The cylinder head will then be capable of crushing the head gasket.

As a result, compression loss between each cylinder would ensue. The damaged gaskets may even cause coolant to leak into the cylinders, damaging other engine parts.

Note that it could be tedious to repair a damaged gasket. You will have to take off the cylinder head for ease of access.

5. Pistons

When an engine overheats, the pistons may expand so much. The expansion could be extreme; there will no longer be enough room for them to expand.

This may cause them to scrape against the cylinders, damaging both in the process. The damaged pistons may lead to severe engine damage. It is also costly to have them fixed.

6. Engine Block Crack

Every component of the engine expands when exposed to heat. It will expand quite a lot when overheating. Although made from solid cast iron, the engine block is susceptible to expansion. The problem arises when the engine overheats.

Some areas of the engine block would expand and then suddenly contract, causing cracks to form.

A cracked engine block is a serious problem because it will cause leaks and the loss of compression. Cracked engine blocks are tough to weld, and often, they are irreparable.

7. Damaged Exhaust Valves

The exhaust valves can also expand when the engine overheats. When they get stuck in the open position, they can cause a loss of compression. If stuck shut, they can cause engine knocking.

8. Burst Radiator and Heater Hoses

Engine coolants may have a high boiling point, but they will still boil when exposed to high temperatures.

When coolant boils and turns to steam, the temperature and pressure they produce are much higher than regular water. The high pressure can sometimes cause hoses to blow off their clamps. Sometimes, they can even rupture and burst.

Frequently Asked Questions (FAQs)

what causes car temperature gauge to fluctuate

Can You Use Water As a Radiator Coolant?

You can use water but only for emergencies. Regular tap water is full of minerals that can deposit into the radiator and metal components. Moreover, water has a lower boiling point, so your engine is more likely to overheat.

Can Your Car Run Without Coolant?

Unless you drive an old Volkswagen Beetle, your car cannot run without coolant. The engine would get too hot too fast that it would immediately shut down after just a couple of minutes.

What to Do When My Car Overheats?

First, carefully go to the shoulder of the road and turn off the engine. Open the hood to let the heat escape. After that, top off the coolant reservoir once the engine cools down enough. If the car does not start, call for a tow truck to bring your car to the nearest mechanic.

Conclusion – Car Temperature Gauge Goes Up and Goes Down While Driving

The usual reason your car’s temperature gauge goes up and down while driving is an issue with the cooling system. Here are some of the many possible reasons why your engine might overheat:

  1. A Malfunctioning Radiator Fan
  2. A Faulty Coolant or Water Pump
  3. A Blown Head Gasket
  4. A Closed Thermostat Valve
  5. Not Having Enough Coolant
  6. A Broken Temperature Gauge
  7. Issues With The ECU

These are only some of the reasons why your temperature gauge would suddenly shoot up while you’re driving. If diagnosed early enough, you can fix the issue before it gets worse.

Read next:

Car Running Hot but Not Overheating

What Are the Gauges in a Car?

“Check Gauge” Light

Radiator Leak [Causes and How to Fix]