The car temperature gauge is a small needle located on the dashboard to show the coolant’s temperature in the engine compartment. The needle shows the cold reading when you are not driving while the indicator moves towards hot during uphill movement because of overheating.
Car temperature gauge can go up and down while driving because of a faulty thermostat, air pockets in the cooling system, leaking and low coolant levels, blown-out head gaskets, failure of the coolant temperature sensor, faulty radiator fans, water pumps, and water control valves.
The car temperature gauge shows a reading between the hot and cold when driving. The small fluctuations are normal because of driving conditions, but many people complain about their frequent up-and-down movement.
| Causes | Solutions |
| Faulty thermostat | Replace the right coolant and replace it |
| Air pockets in the cooling system | Bleed the cooling system to remove air |
| Leaking and low coolant | Add coolant and inspect fluid lines and connections |
| Broken head gaskets | Remove the cylinder head and add new gaskets |
| Failure of coolant temperature sensor | Replace coolant temperature sensors |
| Radiator fan issue | Check the fuse and keep the blades clean |
| Faulty water pump | Add a new water pump |
| Bad control valve | Replace control valve |
Faulty thermostat
The thermostat is located near the radiators responsible for transferring the coolant into the engine’s part. The thermostat senses the internal temperature and draws the coolant according to them to remove heat.
Sometimes the thermostat fails to perform its correct function, and you can see the erratic movement of the temperature gauge on your dashboard.
The issue also comes when thermostat valves get stuck in the closed or open position. These can restrict the flow of coolant or allow their continuous supply.
The thermostat contains metal housing that can rust because of age and develop leakages. You can see the white mist from the exhaust system’s tailpipe.
These can also go bad because of the use of incompatible coolant and their contamination. The issue comes when you do not change the coolant for so long.
Using the right and compatible coolant for your vehicle is better so it cannot contaminate the thermostat valve. In addition, it is necessary to replace it every 30,000 miles to 50,0000 times, depending upon the type and vehicle.
Replace the thermostat valves if these get stuck and are not functioning.
Air pockets in the cooling system
The temperature gauge in your car fluctuates during driving because of air pockets in the cooling system. The engine overheats because of the accumulated air and returns to normal temperature when coolant moves through them.
The coolant system is tightly enclosed to prevent leakages and restrict air and dirt entry into the reservoir. However, the air can find its way to enter the system and disturb its normal function, leading to overheating issues.
Air enters the cooling system because of cracks in the plastic reservoir due to the hood’s high temperature.
Moreover, the damaged or faulty radiator hose caps allow the entry to mix with the coolant. It can also mix with antifreeze solution because of blown-out head gaskets.
It is necessary to bleed the coolant system for air removal. Plan scheduled maintenance once a year of the cooling system and inspect the leakages in fluid lines and ensure their tight connections.
Leaking and low coolant
The leakages and low coolant levels also cause the temperature gauge’s frequent up and down movement.
The coolant starts to leak from the plastic hose because of the faulty thermostat and corroded metal housing. The corroded metal housing develops cracks, allowing the coolant to seep through them.
The issue also comes because of an incorrect size hose cap which can come off and cause the coolant’s boil. You can see a fluctuating needle reading on the dashboard when carrying a heavy load with low antifreeze levels.
Engines need more power to hold heavy loads, and eventually, their temperature increases. Check the coolant level by opening the car’s hood, and you can see a plastic container there.
You can also inspect the fluid lines and radiator hose cap to check the leakages.
Broken head gaskets
Head gaskets make the seal between the cylinder head and the engine components, and these are also helpful in keeping the oil and coolant separate for lubrication and cooling.
Sometimes the head gaskets blow out and cause mixing of coolant with oil. The coolant and oil mixing leaves a milky residue that can contaminate the engine parts.
You can see warping of the head gaskets because of their age and high temperature. These cannot seal the cylinder head properly because of their warped structures and broken seals.
These are less costly to replace, and you can remove the cylinder heads to add new ones.
Failure of coolant temperature sensor
The coolant temperature sensors are located near the base of the radiator. These are responsible for giving the signals to the car temperature gauge for their movement.
It senses the temperature and controls the needle movement according to the coolant temperature. Sometimes the sensors become bad and give an erratic reading on the screen.
The sensors cannot transmit information if the connected wires are broken, or there is an issue in the electronic control unit.
The sensor also fails to function and gives the correct reading to the needle. The issue also comes when these sensors break and provide false information to their connected units.
It is better to replace the sensors if they are broken and malfunctioning. Moreover, you can also identify the fault in the sensors by connecting scanner tools with them.
Radiator fan issue
The radiator fan’s primary function is to cool down the engine components and draw cool air into the hose. The failed radiator fan cannot cool the antifreeze in the radiator hose, increasing the engine part’s temperature; as a result car temperature gauge fluctuates.
These become faulty when dirt, dust, and grime build up on their fan blades. Sometimes the blades can also bend, becoming slow or losing functionality.
In addition, the issue also comes because of bad wiring, blown out fuse, and bad bearing of the radiator fans. Check the fuse of the radiator fan if these are not functioning and replace the blown-out ones.
You can keep their spinning blades neat and clean to remove dust and prevent bending.
Faulty water pump
Water pumps are responsible for circulating sufficient coolant throughout the engine parts. The failure of the faulty water pump causes the up and down movement of the car temperature gauge.
The antifreeze cannot move equally in all engine parts when water pumps fail to perform their function. The malfunctioning of water pumps occurs because of the corrosion and rust on their parts.
In addition, failed bearings, propeller, broken shaft, and sludge buildup lead to failure. You cannot repair the water pumps, and the only solution to resolve the problem is their replacement.
These are not expensive, the replacement procedure is easy, and you can do it at your home.
Bad control valve
The control valve is an integral part of the cooling system and regulates the coolant flow from the hose according to the internal temperature.
Sometimes the control valves become bad or get stuck, and you can see the up-and-down movement of the car temperature gauge during driving.
The failure of the valve occurs due to their age and routine functioning. These can also develop leaks when they get stuck in the open position. You can see white steam coming from the exhaust system because of their leakages.
Replace the failed control valve with a new one for better regulation of antifreeze.
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