Grease Monkey
Grease Monkey

Engine Overheating-Common Causes, Diagnostic Solution and Expected Repair Cost


Engine overheating is not ‘cool’, but what’s not cooler is the many reasons that can make it happen. From a loose coolant hose to a blown head gasket, there are many possible reasons for Engine overheating. 

In this post, we will be listing the most common causes of engine heating, possible solutions and related repair costs.

All price estimates are in USD

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1. Lack of Coolant:

Low coolant levels are the most common cause of engine overheating. After all, it's the antifreeze/coolant's job to dissipate all heat. Low/No coolant level would render the cooling system useless, causing the engine to get extremely hot and smoky.  


Low coolant level is caused due to two obvious reasons: 

  1. Either the coolant has been completely exhausted over time and needs a refill
  2. Or, Coolant has been exhausted because of a leak in the system. 

Generally, the Coolant lasts around 30,000 miles or two years. So if you haven't had a coolant refill in a while, now’s the time. You can also check your coolant level by looking into your coolant reservoir located under the hood. A white, semi-transparent container with coloured fluid (red, green, or orange). 

Again, anti-freeze lasts around 30,000 miles, so if you recently got a refill, and the coolant level is low, you have a probable leak. Just like oil leaks, coolant leaks have spillage as well which can easily be noticed. 

Solution/Repair cost: 

An average car needs around 5 litres of coolant mixture(2.5L antifreeze + 2.5L water) which would cost you around $50. This can be costly depending on the coolant type and requirement. 

In case of a leak, it can be due to a bad hose or leak in the reservoir. Fixing which can go up to $100. However, coolant leaks mainly happen due to leaking radiators, fixing that gets expensive.    

2. Faulty Water Pump:

Water Pumps help regulate the coolant around the engine. It can fail to do so if it's clogged, broken, or leaking. In any case, the engine won’t get the coolant and would overheat. 


Diagnosing a water pump is not easy and you generally need a mechanic for it. By yourself, you can look for symptoms like whining noises from the water pump belt, coolant leaks and rusting or deposits on the exterior. Any of this is enough reason to get your water pump inspected. 

Solution/Repair Cost:

Water pumps last around 60,000 miles, so they don’t fail easily. But when they do, expect to pay around $300 - $500 in repair. You can also have them replaced at around $500 - $600.     

3. Low Engine Oil level:

Although the oil inside a running engine is extremely hot, it is regulated, getting cooled in the oil pan. So, while less effective, engine oil does help keep the engine cool. 

Low oil levels would not only dissipate less heat but since oil lubricates, not having enough would increase friction, increasing the heat generation of the engine.  


If your engine is lacking oil, you will have the oil light turn ON on your dashboard. Another way to check is by using the dipstick.

You can have low oil levels because:

  1. It hasn’t been changed so now it's denser and sluggish. 
  2. Or you have an oil leak that may be in the oil pan, oil filter or from the engine itself due to a blown head gasket. 

By using a dipstick, you can check the oil level and its consistency. If it's dark, dirty and sluggish, you would need an oil change. Otherwise, you can check around the oil filter, oil pan, and engine to know whether you have an oil leak. 

Solution/Repair Cost:

A car needs an oil change every 5000 miles for petrol and 7000 miles for diesel. It is mandatory that you also replace the oil filter with the oil. Both of which cost $50 - $70 if done by yourself, or $100 by a mechanic.

Any sort of oil leak from the oil filter or oil pan is mainly due to loose fitting and can be fixed fairly cheaply. However, leaks caused by blown head gaskets are expensive $1000+.

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4. Broken Radiator/ Fan: 

The coolant gathers heat from the engine and gets cooled down in the radiator. As the coolant flows through the radiator’s metal fins, the radiator fan blows air on it to cool it down. 

In case the radiator gets clogged, develops a leak due to corrosion, or the fan breaks, it would fail to supply cool anti-freeze to the engine and the engine would get overheated. Another way a radiator fails is when there is too much dirt on the radiator fin. This blocks the air to go through, slowing the cooling. 


Start diagnosing your radiator by looking for coolant leaks. If your car has coolant spills upfront, that’s a clear sign. See if the radiator fan is working properly, not making any noises. Also, clean your radiator fins so no dust is there. 

In case of clogging, the coolant would have a noticeable change in colour and smell. Clogging can happen due to contamination, which makes the coolant dirty and thicker in density. 

Solution/Repair cost:

A leaking radiator is either because it's old/ damaged or it has loose/leaking hoses. While a hose can be tightened or replaced for under $150, a damaged radiator might need replacement which can cost between $500 - $2000 depending on the brand.      

If it's clogged, it can be cleared by flushing that may run between $100 - 200.


5. Bad thermostat:

The thermostat’s job is to maintain engine temp by regulating the flow of coolant. If the thermostat fails, proper coolant flow would not be regulated causing the engine to overheat.


A bad thermostat results in many temp related problems. It would fail to give the right temperature reading. The temperature inside the cabin would change randomly, you might have heater malfunction and even coolant leaks. 

Solution/Repair cost:

Fixing a bad thermostat would need a mechanic that may charge between $150 - $300.   

6. Clogged Heater Core:

A heater core is very similar to a radiator, just smaller. When the heater is on, hot coolant passes through it, heating the heater core. A fan blows air over the heater core, warms up the air and gets to the passenger cabin. 

A heater core can cause overheating by either blocking the coolant airflow or leaking it. 


If your car’s heater is not working or is less effective it has gone bad. 

Solution/Repair cost:

Fixing a clogged heater core would require you to get it flushed which can run around $75 - $100. While replacing one would go as high as $1300 simply because it's a complex and time taking process.

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7. Loose/Broken belts and Hoses: 

Multiple modules in a car are belt driven and run by the serpentine belt. This includes an AC compressor, water pump, and even radiator fans in some cars. A loose serpentine belt will limit the functioning of all the components. Like slowing down the water pump or the radiator fan. A broken serpentine belt would render these components useless.     

Similarly, loose/damaged hoses would cause leaks all around. 


A faulty serpentine belt would be loose, and squeaky, making loud noises. Same for the faulty or loose hose, that will have coolant leaking around it. 

Solution/Repair cost:

Bad serpentine belts are replaced, which cost around $25 - $70. Where a loose hose can be tightened, a leaking one can be fixed using simple DIY or replacement. Depending on the type of hose, charges could differ between $20 - $100.  

8. Blown head gasket: 

A head gasket seals the engine combustion chamber. It keeps its pressure-tight while allowing both coolant and oil to move around freely. Since head gaskets are made of rubber, they get brittle over time, eventually causing cracks and leaks. 

The pressure inside blows opens small cracks letting internal fluid come out. The compression inside the engine is also reduced forcing the engine to work harder. All of which result in extreme overheating and ending up in a hood full of white smoke. 


A clear sign of a blown head gasket is oil spills and sluggish performance. Since the head gasket seals the engine when it blows hot oil spills out and burns in the engine bay. The performance is also reduced and the fluid level drops along with it. 


Blown head gasket cannot be repaired. They need replacing which is a labour-intensive job. So while a head gasket costs around $100 to buy, the labour cost goes above $500. All combined the average cost of head gasket replacement is around $1500.