Why Does My Car Temperature Gauge Go Up and Down?

One beautiful morning, you were driving to work and found out your car temperature gauge goes up and down. You become so confused and unsettled. And you are there wondering, “How am I going to fix this mechanical error?” Don’t be perplexed. That’s why we are here to help you troubleshoot this problem and find a diagnostic solution.

First thing first, your car temperature gauge is a dial that measures how hot or cold your engine’s coolant is. Under normal circumstances, your car’s temperature gauge should slowly rise after you start off the car’s engine and have traveled a distance. Well, several things can cause this needle of your car temperature gauge to move up and down erratically.  Stay tuned as we elaborate on these factors below.

What causes Car Temperature Gauge to go up and down?

So, you ask, “What causes my car’s temperature gauge to fluctuate?” A plethora of factors are responsible for this anomaly. In most cases, some functioning parts of the cooling component might have gone wrong. For instance, if you notice the temperature gauge fluctuates from normal to hot, you should suspect a fault-sensitive and inexpensive thermostat.

car temperature gauge hot then normal

Stuck-Closed Thermostat

The thermostat regulates the coolant’s temperature before it returns to cool the engine. Though the thermostat is relatively cheap and replaceable, it can cause trouble for your car once it gets bad. If it gets stuck and refuses to open, the coolant cannot flow to the engine to cool off the engine. This causes the engine to start overheating. When the engine begins overheating, the car temperature gauge can go hot and then return to normal.

After the 1980s, most cars that were manufactured had a closed-circuit type of cooling system with a reservoir tank that features a visible marking to determine the coolant level. It is, therefore, essential to regularly check this level to guard against coolant leakage. If you notice a minute leak, you should rectify the leakage without delay because a low coolant level can cause your car temperature to fluctuate.

If your thermostat is partially stuck, then you are surely going to see your car temperature go down while driving. This is simply because the coolant is constantly being released into the engine, which causes the temperature to drop rather than climb up.

When a thermostat is functioning correctly, it only allows either warm or cool coolant to enter the engine, thus regulating the overall temperature of the car engine. Though a partially stuck thermostat may not necessarily hurt your car, it can surely lead to increased fuel consumption. You are therefore advised to change the inexpensive thermostat than spend many bucks on your fuel purchase. If the thermostat is functioning well, then the gauge may simply be broken.

Engine getting Overheated

Experts have confirmed that when your engine’s temperature goes higher than 2300F, your engine is said to be overheated. If the temperature goes beyond 2450F, serious havoc might happen to your engine. This is more reason you should pay attention to an engine getting overheated.

Apart from a bad battery, one of the many reasons your car’s engine won’t start is that the car’s engine is overheated, accompanied by a significant loss of coolant. The overheated temperature can further warp the cylinder head, thereby weakening the pressure the engine needs to start the car.

Over time, if the issue is not attended to, the pistons end up wielding themselves into the cylinder, which is catastrophic for your car’s engine. This means you will need a complete overhaul of a car engine.

Another similar problem you may notice in your car is that your car temperature gauge goes straight too high. Your first guess can be your engine is overheated. Well, you are half correct! In this case, several reasons can lead to this sudden shooting up of your car temperature.

Your thermostat can be broken, or your car’s coolant level may have diminished. In either case, there is not enough circulation of coolant to cool down the running engine, thereby resulting in it getting overheated.

Lousy Radiator Fan

Closely located to the reservoir tank is the radiator fan. The fan is expected to pull air through the radiator when your car is not moving fast enough to draw in air. Having a failing fan can be erratic and can cause your engine to get overheated. A lousy radiator fan can lead to a fluctuating temperature gauge.

Head Gasket Blown

Perhaps, in recent times you have discovered your car temperature gauge rises then falls. The possible cause of this irregularity is that the head gasket may be defective. Located between the cylinder head and the engine block, the head gasket maintains internal combustion. It allows easy circulation of the coolant and oil throughout the engine for cooling and lubrication, respectively.

Due to serious engine overheating, the head gasket can become warped and cause the oil and coolant to mix together to form oil-coolant. If the oil in the coolant circulates around the engine and the radiator, it can lead to the formation of clogs and sediments which cluster along the coolant passageways. The clogs can prevent the flow of coolant, thus leading to an overheated engine.

Usually, an automobile with a defective head gasket cannot last longer than a month. The engine will be seriously damaged if the blown head gasket is continuously used without replacement. You are advised not to drive your car around when you have a faulty gasket.

A sure way to know you have a blown head gasket is when you notice white smoke coming from the tailpipe, unusual loss of coolant without a leak, and your engine getting overheated.

Bad Radiator

Most drivers experience an unpalatable experience because their car temperature gauge goes up while idling or in traffic. This can be frustrating and confusing for drivers. The most probable reasons can be a broken fan and a bad radiator.

The radiator regulates the temperature of the coolant. When you notice sludges form in the radiator, this means the radiator and its fan has gone wrong and need immediate replacement.

If the radiator is not changed sooner than later, the color of your coolant changes from yellow to rusty color, which means it has becomes inefficient for cooling down the engine. A better alternative to an iron radiator is an aluminum radiator.

The aluminum radiator boasts corrosion resistance, durability, and excellent heat output. Owing to their efficient thermal properties, aluminum radiators provide more heat than any other material.

A related cause for increased temperature while your car is idling is a bad radiator cap. When your car’s radiator cap is not properly sealed, air can penetrate into the radiator, producing air pockets in the heater core and radiator hoses.

The result is that the car engine will begin to overheat since there is no stable temperature of the coolant throughout the engine. Symptoms of a failing radiator cap include an overflowing coolant reservoir, collapsed radiator pipe, and leakage in the coolant level.

Faulty Cooling System

So, if you find your car temperature gauge rising but your car is not overheating, there might be a few reasons: a bad radiator, reduced coolant level, a defective thermostat, or a faulty water pump. A bad water pump can also cause the car’s temperature to move straight too high. A water pump pumps coolant through the cylinder head and engine block, thus regulating the engine’s temperature.

When your water pump develops a fault, it will be unable to pump coolant throughout the engine. This invariably leads to engine overheating. If there is no quick intervention, the cylinder head can become warped, and the head gasket gets distorted, leading to a sudden increase in the car temperature. Often, this can cause the engine to seize up or refuse to start.

A common reason your car temperature gauge goes up and down, and no heat is emitted, is that your cooling system is faulty. You may want to check out clogged components such as the heater core, radiator hose, coolant level, thermostat, or water pump. The coolant passageway might be blocked with sediments or rust. You should consider replacing the rusty components.

The primary reason your car temperature gauge goes up and down while driving is simply because a component in your cooling system is not functioning correctly. This could be the thermostat valve, radiator hoses, radiator fan, temperature gauge, or the coolant itself that circulates around and cools off the engine. You can either invite a professional car mechanic to fix these issues or easily replace most faulty components by yourself. 

How To Fix If Car Temperature Gauge Goes Up And Down

If your car temperature gauge is malfunctioning, it is high time you consider finding out the cause. Should in the case you discover the faulty part, swiftly swing into action and fix this error. Hesitating about repair can cause severe damage to your car.  Below are some simple and practical steps to fix these mechanical errors and a bucket to drain the coolant.

car temperature gauge rises then falls

Replacing a Defective Thermostat Valve

As mentioned earlier, the thermostat is an inexpensive car part that can spell doom for a car if it is not replaced accordingly when it develops a fault. Here is a quick way to quickly fix a bad thermostat. You are advised to get the right tools before following the steps below. These tools include a screw jack, pair of vise grips, screwdrivers of different sizes, an adjustable wrench, an OBDII scanner, a pocket knife, and a small ball-peen hammer.

  • After turning off your engine, allow the car to cool down for about 15 minutes.
  • Locate the position of the thermostat valve. It is usually positioned at the base or top of the car’s radiator.
  • Jack up your car to give you a better clearance.
  • Remove the cap of the radiator.
  • Drain the car’s radiator and safely detach the thermostat.
  • Check if the thermostat is still functioning. To confirm, submerge it in a basin of hot water to see if it opens. If it remains close, then it has become inefficient.
  • Replace the defective thermostat with the new one. Make sure all your coolant plugs are intact before replacement.
  • Start the engine to check if there is a remarkable improvement in the car temperature gauge.

Replacing A Faulty Coolant Temperature Sensor

The coolant temperature sensor (CTS) is typically located near the base of the radiator. One common cause of faulty temperature readings is a broken coolant temperature sensor (CTS). As soon as the CTS gets damaged, the car suffers from engine knocking. Engine knocking happens when fuel burns unevenly in the engine cylinder, which gives off shocks and noise due to pre-ignition.

Typically, the standard cost for replacing a bad temperature sensor ranges between $145 and $195. The fee includes both the price for the part and the labor cost. However, if you wish to buy a new sensor, you should be spending between $65 and $90.

To fix a bad CTS, you need to follow the steps below.

  • To confirm if the sensor is in good condition, you can use an efficient OBD2 scanner to see if it is still working.
  • If the CTS is not functional, then allow your car to cool down for 20 minutes.
  • For better clearance, jack up the front side of the car.
  • Open the radiator’s cap.
  • Drain the coolant/water in the radiator.
  • Ensure you disconnect the CTS wiring connector.
  • Proceed to detach the faulty temperature sensor.
  • Install a new temperature sensor.
  • Proceed to reconnect the wiring connector.
  • Start off your engine and see whether the gauge will work.

Diagnosing Air in the Coolant System

When air penetrates into the radiator, it forms air pockets within the radiator leading to unstable temperature within the engine. This can result in engine overheating. To fix this error, you can eliminate the air by following the steps below.

  • For a better view, jack up your car with the bonnet open.
  • Remove the radiator cap.
  • Start your car’s engine so that coolant can begin to circulate throughout the radiator and engine.
  • With the tilted position of the car, the trapped air in the radiator will begin to burp out.
  • After about 20 minutes of steaming up the engine, all trapped air will be eliminated.
  • You can go ahead to close the radiator cap and lower the car.
  • Drive the car around to see if there are still burping noises.
  • In the absence of noise, you can top up the coolant if it has dropped in its level.

If you have tried the three steps above, and your car gauge still fluctuates, you should invite the service of an auto mechanic. He would check other delicate components within the cooling system and the engine parts and replace them accordingly.

Frequently Asked Questions (FAQs)

What does it mean when your temperature gauge goes up and down?

This simply means that your engine is overheated. An overheated engine can be caused by several factors. These factors may include leakage in the coolant level, a clogged radiator hose, a defective thermostat, a bad water pump, and failed radiator fan. The car temperature gauge might also be the culprit if it has developed a fault.

Is it normal for a car temperature gauge to fluctuate?

Typically, a car temperature gauge is built to last for a long time and slowly rise from cold and stay in the middle. So, when you see the indicator starts fluctuating, you should be quick to check out what exactly is wrong and rectify it without delay.

Should my temperature gauge be in the middle?

The car temperature gauge slowly moves from cold to the middle after driving for a few minutes. The average level of the temperature gauge, when your vehicle is fully working is about the center. Anything apart from this level calls for swift attention.

If the gauge remains in the cold after the engine has run for a very long time, it could mean the car gauge is broken or the thermostat is partially stuck. However, if the temperature gauge goes too high, the engine is overheated and likely caused by a faulty cooling system or warped head gasket.

What does it mean when your temperature gauge stays cold?

Your temperature gauge ordinarily stays cold until your engine has run enough. Then, it starts climbing up slowly. If the temperature gauge is stuck in the cold, the car gauge could either be broken, or the thermostat has gone faulty. If the thermostat continuously releases coolant to the engine, the engine becomes cool and can affect the fuel economy and the car’s performance.

Where should your temperature gauge be on your car?

Typically, there are markings for hot and cold on the temperature gauge. If you observe very well, you will also see a marking in the middle. This middle marking indicates the average temperature for your car. The needle of your car’s temperature gauge slowly moves after you engage your engine.

After a long distance, if your car is behaving normally, the car gauge stays in the middle. Ideally, the temperature for your vehicle should be between 195 degrees and 220 degrees, which is about the middle marking of the gauge.

Final words

Your car temperature gauge might be proving funny as it fluctuates erratically. Common reasons for this irregularity include a lousy radiator, defective water pump, leakage in the coolant level, and faulty thermostat. Also, a blown head gasket can be a chief culprit.

You must replace any defective component as soon as possible to avoid further damage to the car’s engine if you notice your car’s temperature goes up and down. You can replace them by getting the right tools.

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