Why Is My Car Overheating With A New Thermostat? – Solution

Why Is My Car Overheating With A New Thermostat? – Solution

Why is My Car Overheating with a New Thermostat

After visiting the mechanic and replacing the thermostat, the car starts to overheat again. This can be incredibly frustrating as you might need to revisit the mechanic. The fact is that various parts of the car engine can cause it to overheat.

These include a bad water pump, faulty radiator, failing head gasket, damaged belt, failing coolant, and much more.

To make your work easier, we’ve highlighted all the issues that may be causing your car to overheat after replacing a faulty thermostat. These are as follows:

Contaminated Or Low Coolant

Even if you replace your vehicle’s thermostat but still have contaminated coolant, the car will still overheat. The work of coolant is to transfer heat and prevent engine damage caused by boiling or freezing.

Note that heat can only be properly transferred with a liquid in the system. Therefore, it is essential to keep the coolant from evaporating or freezing.

If the coolant is contaminated, it will not flow smoothly. As a result, this will affect the performance of the engine as it will overheat. On top of that, if the coolant is low, the engine will start to overheat. This is because there will be a spike in temperature.

How To Fix It

All you need to do is change the contaminated coolant with the good one. Also, ensure that the coolant level is right all the time.

Failing Heater Hose

Another overlooked reason why your car’s engine may be overheating after replacing the thermostat may be due to a bad heater hose. The heater hose helps to transfer the excess heat, in the form of engine coolant, from the engine to the heater core.

On the same note, it transfers the same heated coolant from the heart core to the engine.

If the heater hose is damaged or has a leakage, the coolant will be lost, and it won’t work effectively in transferring the required amount of coolant. As a result, this will make the engine overheat.

How To Fix It

Replace the damaged heater hose with a new one. The procedure is easy, and any person can replace it. Follow your vehicle’s manual, or you can even hire a mechanic.

Damaged Belt

Even after replacing a damaged thermostat with a new one, a broken belt can cause the car to overheat. The water pump belt is circulating coolant from the radiator, around the engine, and back to the radiator.

Therefore, if this serpentine belt is broken or damaged, it will not turn the water pump at the required speed, which will affect how fast the coolant cools the engine. As a result, it will cause the engine to overheat.

How To Fix It

Maintaining and inspecting the water pump belt is crucial. This is because it is made of rubber and nylon cords that tend to crack or break after some time.

The belt is exposed to high temperatures, which means it has to be inspected often. Change the damaged or worn out belt to prevent the car from overheating.

Faulty Water Pump

Bad or faulty water is another main reason why your car may be overheating. This is because it won’t be in a position to circulate coolant through the engine block. As a result, the engine won’t be cooled. And if not repaired or replaced in good time, this may lead to other serious issues.

How To Fix It

Replace the bad water pump with a new one. It is important to thoroughly flush the cooling system before setting up the new water pump. You should also refill it with the right coolant or else you will have more problems to deal with.

Faulty Radiator

The radiator also plays a significant role in the cooling of the car’s engine. The radiator works by transferring the heat from the fluid inside to the air outside, thus cooling the fluid.

This, in return, cools down the engine and maintains its operating temperature. If the radiator is faulty, it will not cool down the coolant, which means the fluid won’t be able to cool down the engine’s temperature.

Check the radiator cap, radiator fins, and radiator fan if they are working okay. These will let you know if the radiator is working fine or not.

How To Fix It

If one of the radiator parts is damaged, you can either repair them or have them replaced. If there are holes in the cap, you can use epoxy to fill the cracks. But if the damage is severe, you should simply replace the entire radiator.

Clogged Radiator

Despite having a new thermostat, if your radiator is clogged, the issue of your car overheating will not be resolved. One of the things that cause the radiator to clog is a coolant leak. If the coolant is not checked or topped up well, hoses and hose connections will become clogged and start to rust.

After some time, this may cause small holes to come up in the radiator. In the end, the coolant will be lost, and the car radiators’ performance will be affected.

How To Fix It

If you’ve got a clogged radiator, you will start by flushing it. Make sure that all the bad coolant is out before replacing it with a new coolant. Also, before you perform the flush, ensure that all the holes are sealed.

Air In The Cooling System

When the air gets into your car’s cooling system, it causes steam pockets in the line that behaves like plugs protecting the coolant from flowing. For this reason, the engine starts to overheat as the coolant doesn’t flow at its normal speed or stops flowing.

How To Fix It

The easiest way to fix air pockets in the cooling system is by leaving the radiator cap off, turn the engine on, and allow the radiator to bleed out the air. Unlike other cases where you have to replace parts, you don’t have to in this situation.

All you need to do is to bleed the air out. Also, ensure that the radiator cap is sealed properly so that the air doesn’t find its way inside the system.


Since you know which parts to inspect that may be causing your car to overheat, your work has been made easier. Aside from highlighting the parts, we’ve also gone ahead and explained how you can fix them.

Therefore, you should have an easy time repairing your car. Alternatively, you can take it to a mechanic for proper maintenance and repair. But take your time so that you don’t have the same problem again.