A driver taking his eyes off the temperature gauge while at the wheel is highly discouraged, especially if caught up in a traffic jam or such driver is going uphill.
If you are uncertain about why your car temperature gauge goes up and down while driving, then there is no other place to be than here.
This article explains the various reasons your car temperature gauge goes up and down while driving, how to fix it, and an FAQ section to answer some related questions you might have.
Why Car Temperature Gauge Goes up and Down While Driving
If your car temperature gauge goes up and down while driving, it is mostly because of a bad thermostat, a low level of coolant, or air in the cooling system. Also, it could be due to a bad temperature gauge or a defective coolant temp sensor.
So many drivers tend to ask, “why does my car temperature gauge goes up and down while driving?” Several reasons can cause this anomaly.
On several occasions, some parts responsible for the proper functioning of the cooling system might have stopped working. For example, if normal and hot fluctuations are noticed in the temperature gauge, the most likely cause of this is an inexpensive and fault-sensitive thermostat.
Related: Car Temperature Gauge Stays on Cold (Causes & Solutions)
Reasons a Car Temperature Gauge Goes up and Down While Driving
Below are some common reasons why a car temperature gauge goes up and down while driving
1. Stuck-Closed Thermostat
A thermostat that is stuck closed is the most common reason why a car temperature gauge goes up and down while driving.
The thermostat must regulate the temperature of coolants before it goes back into the engine to have a cooling effect. Although the thermostat can be easily replaced and is not too expensive, it could be a problem for a vehicle if it worsens.
Meanwhile, if a thermostat gets stuck and does not open, coolant stops flowing into the engine. Hence, the engine stays warm. This usually results in overheating of the vehicle’s engine. When an engine overheats, the vehicle’s temperature gauge will go up and back to normal.
Vehicles manufactured post-1980s, with cooling systems of closed-circuit nature, have a reservoir that plays the role of a mark that shows the level of coolant in a vehicle level. Hence, checking this level regularly is ideal as it helps to easily know when there is a leakage.
If a small leak is noticed, fix it without wasting too much time because if the coolant level in a vehicle gets too low, it may cause a vehicle’s temperature fluctuations.
If a thermostat gets partially stuck, a definite consequence is that the vehicle’s temperature reduces while driving. This is because there is an uncontrolled release of coolant into the vehicle’s engine, which leads to the vehicle’s temperature decreasing rather than increasing.
A thermostat that works properly only lets in either cool or warm coolant into the vehicle’s engine. Hence, it is in charge of regulating the engine’s temperature. Although if a thermostat should get partially stuck, it may not cause problems for the vehicle, it can only raise fuel consumption.
Therefore, it is advisable to remove inexpensive thermostats from a vehicle rather than spend more money on fueling the vehicle. If a vehicle’s thermostat works properly, but the temperature gauge still fluctuates, a broken gauge may cause this.
2. Engine Getting Overheated
Another reason why a car temperature gauge goes up and down while driving is an overheated engine. Experts and professionals have given an affirmation to the fact that when the temperature of an engine exceeds 230°F, the engine has overheated.
If the temperatures rise above 245°F, then severe problems could be caused by the engine. This makes it a necessity to take an overheating engine as a serious situation.
Aside from having a terrible bad battery, another reason amongst others why a vehicle’s engine may not ignite if the engine is overheating (which is usually caused by a high reduction in engine coolant) is a deformation in the gasket cylinder head, which reduces the pressure required by the engine to ignite the vehicle.
As time goes on, if the problem is left without being solved, the pistons will, later on, get attached to the head cylinder, which is very disastrous for a vehicle’s engine. This problem will require that a vehicle’s engine be changed completely.
Another likely issue that may spring up in the vehicle is that the vehicle’s temperature gauge goes high straight up and not gradually. The first thought will likely be that the engine has heated beyond normal. Well, this is partially correct, as several factors could be responsible for the sudden increase in the vehicle’s temperature.
The vehicle’s thermostat might have broken, or the vehicle’s coolant level may have gone low. In either situation, there is a limited flow of coolant into the running engine, which means the cooling effect of coolant on the engine is limited, and this leads to the engine overheating.
3. Faulty Radiator Fan
A faulty radiator fan is another reason why a car temperature gauge goes up and down while driving. The radiator fan is found very close to the reservoir.
The fan is responsible for pulling air through a vehicle’s radiator when the vehicle is not accelerating enough to pull in air. If a radiator fan fails, it may be disastrous and cause the engine to overheat. A noisy radiator fan may cause fluctuations in the temperature gauge of a vehicle.
4. Blown Head Gasket
If a car temperature gauge goes up and down while driving, it may be the result of a blown head gasket. The head gasket can be found in the middle of the engine block and cylinder head.
The head gasket is responsible for maintaining internal combustion. It eases the flow of oil and coolant and round the vehicle’s engine for lubrication and cooling, respectively.
If an engine should get seriously overheated, deformation of the head gasket is a possibility which will make coolant and oil mix up and form an oil-coolant combo.
The oil circulation through the radiator and engine can cause sediments and clogs to start forming in the engine, which could block the coolant route. The clogs are capable of stopping coolant from flowing properly, hence, causing the engine to overheat.
Generally, a vehicle with a damaged head gasket will last for a maximum of one month. If a blown gasket is used for a while and not changed, it causes serious damage to the vehicle. Hence, not driving a vehicle when its gasket is faulty is strongly advised.
Certain ways to confirm if the head gasket of a vehicle is defective are when white smoke is being released from the exhaust, an abnormal reduction in the quantity of coolant with no visible leak, and an overheated engine.
5. Bad Radiator
Another reason why a car temperature gauge goes up and down while driving is a bad radiator. A lot of drivers go through terrible experiences due to a rise in the vehicle’s temperature while either in traffic or at idle.
When this happens, it confuses and frustrates drivers a lot. It is most likely that this is happening due to a damaged fan or bad radiator.
The radiator must regulate the coolant’s temperature. When a formation of sludge in the radiator is noticed, this could indicate a problem with the radiator, including its fan that requires immediate replacement.
If the replacement does not occur in time, the coolant starts to change to a rusty color from yellow, which means such coolant can no longer have a cooling effect on the engine. A preferable substitute for iron radiators is aluminum radiators.
Aluminum radiators are resistant to corrosion, durable, and have a very good heat output. Due to their efficient thermal composition, no other material provides as much heat as aluminum radiators.
A damaged radiator cap is similar to why a vehicle’s temperature increases while a vehicle is idle. When a vehicle’s radiator cap is not sealed as it should be, air may penetrate and enter the radiator, producing air pockets in radiator pipes and heater matrix.
The consequence is that t he vehicle’s engine starts overheating due to the coolant’s unstable temperature around the engine. Some signs that may show up when a radiator cap fails to include a reduction in coolant level, collapsed radiator hose, and the coolant reservoir may start overflowing.
6. Faulty Cooling System
If a car temperature gauge goes up and down while driving and the vehicle is not too hot, several factors could cause this. They include; a low coolant level, a damaged radiator, a faulty thermostat, or a defective water pump. A defective water pump can also make the vehicle’s temperature go up to its peak. Water pumps transfer coolant around the engine block and cylinder head; hence, it is responsible for regulating the temperature of an engine.
When a water pump gets faulty, it is usually unable to pass coolant around the engine. This will cause the engine to start overheating if quick attention is not given to this problem. In that case, a deformed cylinder head could be the next problem to face, which has an overall effect on the head gasket.
Usually, this may lead to the engine seizing or refusing to start. A common reason a vehicle’s temperature gauge fluctuates without any heat emission is that the cooling system has become faulty.
It is advisable to check some components like the heater matrix, radiator pipe, coolant level, water pump, or thermostat that might have clogged up. The routes through which a gathering of rust or sediments might have blocked coolant moves. Hence, replacing rusty parts of the cooling system from time to time is advised.
The major reason why a vehicle’s temperature gauge fluctuates while a car is in motion is that a part of the cooling system is unresponsive. It could be several things, including the radiator fan, thermostat valve, temperature gauge, radiator pipes, or even the coolant. Engage a professional mechanic to help solve these problems or replace these faulty components yourself.
7. Air Trapped in the Cooling System
Air trapped in the cooling system is another reason why a car temperature gauge goes up and down while driving. Take a vehicle out for a quick drive, and observe the gauge while stuck in traffic for about 30 minutes.
If the gauge goes down, it is safe to say the air is trapped somewhere in the cooling system. Locate where this happened and have it fixed without wasting too much time.
8. Internal Corrosion in the Radiator or Engine Parts
Internal corrosion in the radiator or engine parts can be another reason why a car temperature gauge goes up and down while driving. This cause is more difficult to locate because internal components are not easy to look at.
However, still, check them closely if no other component shows any sign of being worn. Replacing these components entirely is the only way to fix this problem.
If you cannot determine the component responsible for the temperature gauge fluctuations, get a mechanic to examine the vehicle. A full inspection should be carried out on all components. Spending a little money on an inspection is better than spending a lot more later.
9. Low Coolant in the Cooling System
Another reason why a car temperature gauge goes up and down while driving is when the cooling system has a low quantity of coolant. If the engine has a small quantity of coolant moving around it, the temperature will increase to dangerous levels, and the vehicle will start to overheat. Coolants are essential fluids required by a vehicle to maintain an optimum level.
Coolant helps release heat produced by the engine to allow the radiator to pass it safely into the atmosphere. When the coolant in an engine is less than what is needed or in a situation where it misses its route in the system, this will lead to overheating.
The warning indication is that the car temperature gauge goes up while driving; however, it goes down after operating normally for a while. If the vehicle is not driven for too long and too hard, then there is no real cause to worry.
Meanwhile, if the engine overheats consistently, replacing the coolant immediately becomes necessary. This will allow the cooling system and the radiator to function at the optimum level again. Look at the coolant level, too, as it is not all about replacing one and leaving out the other.
Also Read: Temperature Gauge Rising but Car Not Overheating (Causes & Solution)
How Does the Car Temperature Gauge Work?
A vehicle’s temperature gauge monitors the operating temperature of a vehicle’s engine. It is usually found on the vehicle’s dashboard, close to the speedometer. Its duty is to measure the temperature of the coolant, which helps a driver know how cold or hot an engine is at any particular time.
The water pump assists in circulating coolant around the system. When coolant gets into the engine, it heats up. Then, it gets cool when it reaches the radiator. The thermostat is responsible for regulating how coolant flows. Near the thermostat is a temperature sensor that passes the signals required by the temperature gauge for its readings.
Knowing the regular operating temperature of a vehicle is vital in determining whether the needle is in a normal position. For cold engines, the gauge usually drops down to the bottom of the gauge. In a lot of vehicles, the normal operating temperature reads at 122°F.
Once a vehicle starts, the engine begins to warm up. While getting warm, the coolant receives heat to balance the temperature. After the engine adequately heats up and other parts have started working, the temperature gauge usually reads between 180 – 220°F.
These temperatures should be maintained until the vehicle is turned off. When this happens, the coolant does not flow any more, and the vehicle’s temperature starts reducing.
How to Fix if Car Temperature Gauge Goes up and Down While Driving
If a vehicle’s temperature gauge starts to malfunction, it is a sign that the cause of this needs to be investigated. Peradventure, the cause of this problem is discovered, start acting upon it immediately and have the error fixed. Wasting time on repairing may cause serious damage to the vehicle.
There are some easy and practical ways to correct these mechanical issues, and also, try getting a container for the coolant.
1. Replace a Defective Thermostat Valve
As stated earlier, vehicle thermostats are not so expensive to replace. However, they may cause serious problems for a vehicle if it gets faulty and their replacement is delayed. Here is a way to quickly solve the problem of a defective thermostat.
Getting the right equipment before engaging in this procedure below is strongly advised. These tools include different sizes of screwdrivers, vice grips, an adjustable wrench, screw jack, OB2 scanner, a pocket knife, and a small ball-peen hammer.
- After the engine is turned off, leave the vehicle for 15 minutes or more to allow it to cool down.
- Find where the thermostat valve is placed. It is often placed at the bottom of the radiator.
- Jack up the vehicle to get a clearer view of the lower part of the radiator.
- Take out the radiator cap.
- Drain the vehicle’s radiator and carefully remove the thermostat.
- Check whether the thermostat is in good condition. To ascertain this, drop the thermostat in a container filled with hot water and check if it opens. If it does not open, then it is no longer efficient.
- Remove the inefficient thermostat and put a new one in its place. Ensure every coolant plug is in its place before replacement.
- Start the engine and observe if any remarkable improvement has occurred in the vehicle’s temperature gauge.
2. Replacing A Faulty Coolant Temperature Sensor
A coolant temperature sensor (CTS) can be found close to the radiator’s base. One common reason temperature readings may be faulty is when the CTS is broken.
Immediately it gets damaged, and the vehicle’s engine starts knocking. An engine knocks when fuel does not burn properly in an engine cylinder, and this act causes noise shock as a result of pre-ignition.
Generally, the standard price to replace a defective temperature sensor is around $145 to $195. This fee also includes labor costs. Although, getting a new temperature sensor will only cost about $65 to $90.
Fixing a bad Coolant Thermostat Sensor can be easily done by following the procedure below.
- To ascertain the condition of the sensor, whether it is good or not, use an OBD2 scanner to know if it is still working.
- When it is discovered that the CTS is no longer working, leave the vehicle alone for about 20 minutes to cool off.
- To get a better view, jacking the front area of the vehicle will help.
- Take off the cap of the radiator.
- Drain the content radiator off its content.
- Ensure that the coolant thermostat sensor wiring connector is disconnected.
- Then, go on and take out the defective temperature sensor.
- Put a new sensor in its place.
- Then, go ahead and reconnect the CTS wiring connector.
- Start the engine and observe if the gauge has started working.
3. Diagnosing Air in the Coolant System
If air should get inside the radiator, it starts to form air pockets, resulting in the engine having an unstable temperature. The engine may also start overheating as a result of this. To fix this problem, the procedure below teaches how to take the air out of a radiator.
- To have a good view of the radiator, jack up the vehicle without closing its bonnet.
- Remove the cap of the radiator.
- Start the engine to allow coolant to move around the engine and radiator.
- With the vehicle tilted, the air trapped inside the radiator starts burping out.
- After heating the engine for up to 20 minutes, all air trapped inside the radiator would have been passed out.
- Then proceed to close the radiator, after which the vehicle should be brought down.
- Drive the vehicle around to confirm if any burping sound still occurs.
- If no sound is noticed, top it up if the coolant has reduced.
If the vehicle’s temperature gauge continues to fluctuate after undertaking the above procedure, engage a professional mechanic for assistance. The mechanic will most likely check some other components of the cooling system and the engine and fix them accordingly.
4. Fill Cooling System
The average price of a good quality coolant flush ranges from $65 to $150. Although, this is something that can be fixed without the help of an auto mechanic.
Take out the content of the radiator and pour some distilled water into it till it’s full. Start the vehicle and keep it running for about 10 minutes. Then, turn the engine off and remove the unclean water from the radiator. Pour the new coolant mixture into the radiator, as specified by the vehicle manufacturers.
5. Replace Computer Module
Doing this will cost a whole lot, and no other option listed above is as expensive as this. Averagely, buying a new Engine Control Module will cost up to $300 – $1,500, including a labor fee.
Code scanners can detect if the Engine Control Module has a problem. Another uncommon sign that may show up is a failing central hub.
Frequently Asked Questions – Car Temperature Gauge Goes Up And Down While Driving
Is it normal for temp to fluctuate while driving?
If, while driving a vehicle, the gauge maintains a low, high, or fluctuating status, it is a big possibility that the thermostat is responsible for this. The thermostat works as a regulator for the flow of coolant in a vehicle and helps keep the engine at a very good temperature while it is working.
Why does my temperature gauge go up when I accelerate?
Considering the thermal laws of physics, the heat produced by the engine mixes with the coolant to balance the difference in temperatures. The temperature gauge starts going up until the engine reaches its highest running temperature, usually between 180 to 220°F.
Why is my car temperature going up but not overheating?
The problem of a vehicle’s temperature going up with the engine not overheating could be caused by the radiator having an inadequate quantity of coolant, a defective thermostat, a damaged radiator, a blown head gasket, a defective temperature gauge or sensor, or a defective water pump.
Why does my temperature gauge go down when I accelerate?
If a vehicle’s temperature gauge goes down when accelerating, it could indicate that the thermostat is letting excess coolant into the vehicle’s engine from its radiator, which in effect reduces the heat produced by the engine, which is an abnormal thing that needs to be cheeked.
Conclusion – Car Temperature Gauge Goes Up And Down While Driving
A vehicle’s temperature gauge may rise or fall based on the temperature outside. Nothing is wrong with this; however, if it does not return to its normal state, something might have gone wrong with the cooling system or the radiator.
It should not be ignored if something has gone wrong with either of these components. The sooner it is repaired before it causes more problems, the lesser the repair expenses will be.
Hopefully, this article has, in one way or the other, provided answers to some questions bothering drivers on the causes of fluctuation in a temperature gauge and ways to fix this problem when things go wrong.