Why Is My Car Overheating When Idle?


With the onset of warm days, many automotive owners have problems with the engine overheating when idle.

This problem can overtake anyone. Therefore, all car drivers should know what causes the engine to overheat and how to cope with this task.

How to tell if the engine is overheated

The following signs tell the driver that the engine is overheating:

1. Many cars are equipped with an arrow indicating the temperature of the coolant or a warning sensor on the dashboard indicating that the engine is overheating. Sometimes an additional sound signal is activated.

2. Even if you don’t notice anything, other unpleasant factors will notify you about overheating. First, there may be a loss of motor power, this will be clearly noticeable by the “heaviness”. Secondly, the parts expanded by the increased temperature will start to knock, which will lead to further breakdowns.

3. If you suspect that the engine is overheating, open the expansion tank cap when the engine has already cooled down, and examine it for the presence of a dark foreign plaque. Pay attention to antifreeze, which may contain gray “flakes”. If at least one of the factors is present, it can be interpreted solely as overheating of the motor.

4. Cars with an additional belt of both the pump and the generator signal overheating in another way – the battery charging lamp lights up along with the engine overheating lamp. This indicates a broken generator belt and pump. But the indication of low battery appears only in conjunction with a rise in temperature. If this is not the case, then the problem is solely in the battery.

5. Perhaps the most unambiguous symptom of engine overheating is steam from under your hood. In the first case, it comes from the radiator of the heater.

What causes an engine to overheat at idle

Idle speeds cause the temperature indicator arrow to rise to the maximum.

So why does the engine overheat when idle? The problem may be hidden in the following vehicle parts:

Water pump impeller malfunction. 

This element in the system is responsible for proper circulation.

If there are faults in it, then while the engine is idling, the antifreeze begins to stagnate in the block.

As a result, the coolant boils and the engine overheats.

To solve this problem, there is only one solution – the installation of a new water pump.

Broken pump belt. 

When the belt breaks, the fluid stops circulating and the temperature in the engine begins to increase.

You will be able to understand the problem visually. Sometimes the water pump gets stuck. If this happens, you will hear the belt screeching as it slides over the sheave.

You can’t replace this part yourself.

It is not recommended to go on your own to the car repair shop, it is better to reach it with the help of a tow.

Bad thermostat. 

This part is very vulnerable during hot days.

The thermostat is responsible for the normal operation of the engine.

If there are problems in it, the motor will be poorly heated, and because of this, its operating temperature will increase.

The solution to this problem is to replace the faulty part with a new one.

Some car owners simply remove the thermostat for the summer and the car is already safe to drive until the fall, and then it is again installed in its place.


The gaps between the radiator honeycombs are quite small, and may gradually become contaminated by representatives of the insect world.

This is not a joke, there was a case when minor contamination of the radiator (coupled with poor engine condition) – led to constant overheating of the car.

Keep the radiator clean, and at least sometimes blow it with compressed air.

Engine wear-out:

This can include many aspects, but in most cases, it is the wear of the piston group.

During the long-term operation of the car, the piston rings that serve to seal the combustion chamber wear out, which leads to a decrease in compression, a violation of fuel combustion, loss of power and overheating of the car.

To put it simply, the fuel burns better at a certain pressure that is created in the combustion chamber.

The pressure is about 12 atmospheres.

If you take a pipe, plug it with a potato and blow it inside, you will create a pressure inside, which is called compression.

The force with which You blow will represent the expansion force of the fuel during combustion, which puts pressure on the piston and rotates the crankshaft.

The rings are used for a tighter fit of the piston to the cylinder (in our case, the potato and the tube). Now, if you put a piece of potato, loosely fitting, and blow – the air will pass by the potato-piston.

This is what happens in the engine when the piston group wears out (ring wear and cylinder wall wear).

As a result, part of the fuel expansion energy during combustion passes by the piston (between the piston and the cylinder), and compression is reduced (the optimal pressure in the combustion chamber), which worsens the quality of combustion.

Radiator Fan:

In some (older) car models, this reason was absent, since the fan was driven directly from the crankshaft through the belt. Now, the fans are electric and turn on when the temperature sensor is triggered.

The sensor may not work, and the fan may not turn on. This is a fairly common reason. Just go out and see if the engine connection contacts are oxidized.


A pump forcibly distills water to improve circulation.

Two things can happen to the pump: it will simply leak or the pump impellers will be worn out.

When the impeller wears out, the pump is slow at pumping the liquid, as a result, the liquid in the engine heats up faster than in the radiator (water circulation worsens) You can determine this by the uneven heating – the radiator is cold, and the engine is boiling.

It is important to keep in mind that those symptoms are the same ones you would get if your thermostat is faulty and there is an airlock

There may also be other reasons — one of which is from the category of “you can’t make it up on purpose”.

For example – the handbrake is not fully relaxed, which causes the car to slow down, increase the load on the engine, and overheat.

The handbrake can also get stuck making the car slow down slightly, which is enough for it to heat up

Let’s end it here. Next, we’ll talk about engine overheating in traffic.

Car overhating in trafiic:

When driving a car for a long time in low gear, the engine works with increased power, which in itself leads to overheating.

while also having a lack of counter-flow of air needed to cool the radiator.

What should I do?

The main thing is not to panic. Short-term overheating is not terrible, but if you see that the car is not cooling down, it’s time to act.

If there is overheating, but the temperature has not reached a critical point, then it is better not to turn off the engine immediately.

It is optimal to immediately reduce the speed, then stop the car and let the engine run for another couple of minutes.

Don’t even try to put water in the radiator. this will definitely result in a visit to the car mechanic. 

If the car is overheated try to pull over to the side of the road, if you cant, don’t panic,  it’s important to save the engine.

stop the car, turn on the ac on max and wait, if after 5-10 minutes the situation doesn’t get better – turn off the engine 

It wouldn’t be superfluous to open the hood as well.

The only reason you should stop the engine if there is steam from under the hood.

Most likely, the cooling pipe burst and further engine operation will only worsen the situation.

How to prevent a overheated car engine

There are several rules that a driver can follow to protect the engine from overheating. First of all, it is necessary to occasionally monitor the level of the coolant.

If a drop in the coolant level is detected, add more cooling liquid. Otherwise, serious problems may arise.

The thermostat should be monitored periodically, this isn’t hard and you can even do it by touch.

To do this, just touch the radiator with your hand.

A cooled thermostat is a sure sign that it is faulty. To diagnose it, remove the thermostat and lower it into the water.

Then heat the water to 80 degrees Celsius.

When the water is heated to the set temperature, the valve must respond. If this does not happen, the thermostat must be replaced with a new one.

It is necessary to sometimes subject the cooler pipes to revision.

They should not have holes, cracks, or other damage. The narrowing of these channels is fraught with a violation of the quality of heat removal from the surface of the motor.

It should also be taken into account that even the most microscopic holes in the channels of the cooler can cause leakage of the cooling liquid.

At least occasionally it is worth checking the sealing of the cooling system, the upper part of it.

First of all, The air should not get there, otherwise, the pressure will drop, which will reduce the pressure of the liquid circulation.

You can not ignore the fan operation. As a result of its damage and stopping, the motor will start to overheat with all the previously mentioned consequences.

Now you know how your car’s engine can overheat, how to identify this problem, and what precautions to take. Follow these simple rules, and have a good trip!

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