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Car Still Overheating After Replacing Thermostat And Water Pump – 7 Causes

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Car Still Overheating After Replacing Thermostat And Water Pump

When a car overheats, the most common fix is replacing the thermostat and water pump. However, the car will sometimes overheat after this fix, indicating more problems. 

Why is your car still overheating after replacing the thermostat and water pump? That could result from a faulty head gasket, a malfunctioning radiator, or a cracked head cylinder. Sometimes, the cooling fan is stuck or broken, the drive belt is worn out, or the temperature sensor is damaged. 

Read on to learn how to diagnose overheating issues, how to fix them, and how much the repairs cost. 

Car Still Overheating After Replacing Thermostat And Water Pump

Car Still Overheating After Replacing Thermostat And Water Pump

Several issues can cause your car to overheat even after you swap out the water pump and thermostat. They are discussed below.

1. Faulty head gasket

The head gasket seals the engine, maintaining the compression required to burn the fuel mixture. This seal also helps keep the coolant and oil in the engine and prevents leaks. 

A blown head gasket will cause the engine to leak oil. Since oil helps lubricate the engine and reduce friction, low oil levels can lead to overheating. A faulty head gasket will also allow coolant to leak, causing the engine to overheat. 

Faulty head gasket

You cannot fix a blown head gasket, so the only repair is a replacement. However, since replacing a head gasket involves taking apart the engine, it is a complicated and time-consuming repair that’s best left to a mechanic. 

2. Warped cylinder head

Similar to the head gasket, the cylinder head sits on the engine and maintains compression. It also has valves that allow air into the engine. A warped  cylinder head causes overheating because it restricts the motion of pistons and interferes with airflow into the engine.

There are two main ways a cylinder head gets damaged; warping or cracking. A qualified mechanic can flatten a warped cylinder head back into shape. On the other hand, a cracked cylinder is beyond saving and must be replaced with a new one. 

Warped cylinder head

3. Faulty radiator hoses

Hoses help transfer coolant between the radiator and the engine. They can clog due to debris build-up and burst when hot coolant expands within them. Clogged, constricted, or burst hoses interfere with coolant flow, causing the engine to overheat. 

Though you can patch up radiator hoses, the best thing to do is replace them with new ones. If the hoses are clogged due to debris, flush them to clear out the debris.

Faulty radiator hoses

4. Cracked drive belt

A drive belt’s job is to power the compressor, alternator, water pump, and fan clutch by transferring power from the engine. If the drive belt is cracked or damaged, it won’t power the water pump, so coolant won’t circulate in the engine. As a result, the engine will overheat. 

The best fix for a damaged drive belt one is swapping it out for a new one.

Cracked drive belt

5. Faulty radiator

The radiator’s main function is to remove heat from the engine and keep it cool. It works with the water pump to get hot coolant, cool it, and then send the cooler liquid back to the engine. 

If your car overheats even after replacing the water pump, the radiator is most likely malfunctioning. 

Faulty radiator

Find a good radiator sealant and follow the process below to fix any leaks;

  • Open the radiator cap and pour in the sealant. Do not drain any coolant in this step
  • Fill up the radiator with coolant to the recommended level
  • Run your engine for 10 minutes to circulate the coolant and sealant. This way, the leaks will be closed by the sealant
  • Top up the radiator coolant and let the car sit for a day

6. Faulty cooling fan

Your car’s cooling fan only kicks in when the engine is running while the car is stationary. It may also turn on when the engine temperature is too high and is typically activated by the thermostat.

If your car overheats after replacing the thermostat, your fan may be stuck. A stuck cooling fan isn’t able to rotate, so it can’t push air into the engine and cool it. The fan’s circuit may also be faulty, making the fan unresponsive. 

Faulty cooling fan

In case your cooling fan is stuck or touching some other engine components, move it so it can rotate freely. Replace melted wires or blown fuses to fix the fan circuit. Finally, if the fan is beyond repair, replace it with a new one.

7. Faulty sensor

Sensors like the coolant temperature sensor monitors the engine to ensure it operates optimally. If the temperature sensor is inaccurate, the cooling fan may fail to turn on, leading to overheating.

The best fix for a bad temperature sensor is to replace it with a new one.

Faulty sensor

Signs That Indicate Overheating Problems? 

If you’ve replaced the thermostat and water pump, and your car is still overheating, use the table below to diagnose the problem.

Signs That Indicate Overheating Problems? 
Components to checkSigns to look for
RadiatorCoolant leaks under the car
Discolored coolant fluid
Head gasketThe engine will lose power 
White smoke out of the exhaust
Engine oil contaminated with coolant and coolant contaminated with engine oil
Low coolant level without obvious leaks
Drive beltAC and power steering malfunction
Weird squealing noises from under the hood
Cylinder headEngine misfires 
Smoke coming out of the hood
Low coolant levels without visible leaks
Radiator hosesLow coolant levels
Crust formations where the hose connects to the radiator
Coolant leaks along the hoses
Constrictions or burst sections
Soft, swollen patches due to the pressure of coolant expansion
Cooling fanBlown fuse or melted fan circuit wires
AC performs poorly or refuses to turn on
Loud whirring noises when the fan is stuck
Engine coolant temperature sensorCheck engine will turn on
Black smoke out of the exhaust
Poor gas economy

How Much Does It Cost To Fix Overheating Problems?

How Much Does It Cost To Fix Overheating Problems

The prices of the replacement parts, like the fan and head gasket, range between $20 and $350, while labor costs are around $75 to $130 per hour. Since replacing parts like the head gasket is time-consuming, total repair costs can be more than $1,000. 

However, if you have to replace the engine, the cost lies between $2,500 and $10,000, or more, depending on engine size and car model. 

How Can I Stop My Car From Overheating?

How Can I Stop My Car From Overheating

Fixing an overheating car can be highly expensive, so it’s wise to prevent the problem. Here are a few tips on how to stop your car from overheating;

  • Check your radiator and radiator cap regularly and ensure it is in good condition
  • Monitor and regularly top up the coolant in the radiator so that it never falls below the recommended level
  • Regularly check the engine oil level and its condition. If the oil looks contaminated, change it immediately
  • Avoid overusing the car’s AC because that can increase the likelihood of overheating
If your car is still overheating after replacing the thermostat and water pump, you may be interested in our articles on car blowing white smoke but not overheating and car still overheating after replacing head gasket. These articles provide valuable information and solutions to common car overheating issues, such as head gasket failures, coolant leaks, and other cooling system problems. Whether your car is blowing white smoke but not overheating or it’s still overheating after replacing the head gasket, our team at Car Problem Solved can help you diagnose and fix the problem.
How Can I Stop My Car From Overheating


Here are some answers to questions about overheating problems. 

Q: Can I drive my car to the garage when it overheats?

No. You should never drive your car with an overheating engine because that can cause permanent damage to the engine. 

Q: How long can an engine survive overheating before it’s damaged?

An engine can only survive overheating for a maximum of 1 minute. So, if you think your car is overheating, stop it immediately.


If your car still overheats after replacing the thermostat and water pump, some underlying problems are causing the issue. The fault may lie with components like the cooling fan, radiator, head gasket, sensors, head cylinder, or even the drive belt.

And fixing overheating issues typically involves swapping out parts for new ones. These replacements can cost anywhere between $200 and $10,000, or more depending on what part you’re replacing. Fortunately, overheating can be avoided by checking coolant and oil levels regularly.

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