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Why Is My Car Overheating Even With Coolant


The cooling system is responsible for keeping the engine temperatures of your car at a low enough level that the mechanical parts won’t melt. Gasoline fires burn at 1733 degrees F and the optimal car temperature is around 200 degrees. A car without a proper cooling system can reach up to 400 degrees F which can do some serious damage to a vehicle.

So why do cooling systems fail? The most simple problem to mitigate is that your coolant itself has issues. In some cases you may have enough coolant, but if it is old it will still boil and be rendered useless. There could be a few reasons why your car is overheating and in some cases it may not just be one of them. Thermostat, water pump, serpentine belt, radiator, fuses, cooling fan, or an airflow issue could all be causes to your problem.

Reasons Your Car Could Be Overheating, Even If It Has Enough Coolant

  • Thermostat
  • Water Pump
  • Water Pump Belt
  • Radiator Damage
  • Airflow issues
  • Fuses
  • Cooling Fan
  • Non volume related coolant issues

There are quite a few mechanical parts involved in the cooling system of your vehicle. We’ll get into the specifics of how these parts work and why they can cause your cooling system to fail, but it will first be helpful if you have a rudimentary idea of how the cooling system works.

There Could Be More Than One Reason Why The Cooling System Isn’t Working

Sometimes when it comes to car repairs, it is one problem that causes multiple breaks.

Overheating will break your car. Radiator cracks, warped engine parts, blown head gaskets. The components of the cooling system rely heavily on one another and removing one will put extreme stress on the rest of the system. For this reason, it is not uncommon to find multiple issues within the cooling system, especially after a car has overheated.

The moral of the story is that you need to do a thorough job in testing the entire cooling system when diagnosing your problem.

Basic Cooling System Knowledge

The first thing you should know about cooling systems, is that there is little to no variation when it comes to the different vehicles on the road. Most cooling systems operate the exact same way. Which is great for making this lesson simple.

Temperature Is Important: The car wants to run at a certain temperature. It doesn’t want to be any cooler or warmer than that optimal temperature which for most cars is somewhere between 195 degrees and 220 degrees F.

The car doesn’t want coolant cooling down an already below optimal temperature so it prevents coolant from entering the engine. This is the job of the thermostat to accurately read the engine temps and to open or close the valve that allows coolant to flow.

When a car reaches operating engine temperature, the thermostat signals the water pump to kick on. The water pump pushes coolant fluid out of the radiator and into the front of the engine.

From there, the engine coolant circulates around the cylinders, effectively removing heat. At this point, the coolant enters the head, where it cools off all of the valves. Once this is complete, the fluid goes back out of the cylinder head and back into the radiator to be cooled down. 

The radiator is essentially a system of thin piping that spreads the hot coolant out giving it more surface area to cool off using the airflow from the moving vehicle and the airflow created by the cooling fan.   Once cooled, the engine coolant is recycled and is put back use entering the engine block once again. 

As we previously mentioned, there is a thermometer which is a temperature-controlled valve in the engine. The thermostat reads the temperature and opens and closes a gauge depending on the reading.

The valve opens more when the engine is hotter allowing coolant to flow and do its job removing heat from the engine block. When the engine is cold, your thermometer will signal this gauge to remain closed, remember a car manufacturer wants their vehicle to burn fuel as efficiently as possible for rating and testing.


How The Thermostat Works

The thermostat is responsible for reading the engine temperature and deciding when to allow coolant to flow through the cooling system. Your car want’s to optimize its performance. It is designed to be as efficient in fuel consumption and power output as possible. The engine reaches an optimal temperature to do this that is relatively high (but not too high).

Because of this, the engine coolant is kept out of your car when you first start it. The car needs to get warm. The thermostat opens when the optimal temperatures have been reached to it consistent and not so hot that the engine will melt.

If the thermostat is broken and is always reading that your engine is cold, it will not allow the coolant to circulate. 

Whether your coolant is trapped in the radiator, or in the engine block, you’ll find the same result, engine overheating. 

Common Issues With The Thermostat

  • Being stuck in the on or off position
  • Inaccurate temperature readings
  • Coolant leaking around the thermostat
  • Corrosion and surface scaling.

Signs That Your Thermostat Isn’t Working Properly

  1. Erratic temperature readings
  2. Engine overheating (duh)
  3. Leaking around the thermostat and onto the ground beneath your car

Water Pump

What The Water Pump Does

The water pump in my opinion is mislabeled. It doesn’t ever pump strictly water, and if it is pumping water and only water, you have your answer why your engine is overheating because that water is boiling in your cooling system. I digress. The water pump is the mechanism that pushes water through the cooling system. 

The standard vehicle water pump is powerful! It is capable of emptying  a small swimming pool in under an hour. In your vehicle this translates to full coolant circulation 20 times per minute! If the coolant is not being circulated properly, it may begin to boil, rendering it useless in accepting heat from your running car, thus an overheating engine. 

Common Issues With The Water Pump Include

  • Erosion
  • Leaks

Signs That Your Water Pump Is Failing

  • There is a coolant leak from the front center of the car
  • There is noticeable rust and corrosion on the water pump
  • The belt is making noises
  • Engine overheating
  • Steam escaping through cooling system

Water Pump Belt

The water pump is powered by a belt known as the serpentine belt. The serpentine belt powers several important components of the car at once. The belt is powered by the car’s engine and is responsible for transferring this energy to other parts of the car like the electrical system, power steering system, cooling system, and air conditioning. In some vehicles also power the power braking system using the serpentine belt.

The water pump belt is responsible for powering the flow of coolant and pushing it through the cooling system. When there are issues with the belt, it can lead to engine overheating. 

Common Issues With The Water Pump Belt

  • Breaking 
  • Loose/ Worn out
  • Whining or whirring belt noises

What Happens If The Water Pump Belt Breaks

When a serpentine belt breaks, the entire water pump will typically lose power. In these scenarios, if the car manages to stay drivable, the engine coolant will not be pushed into the radiator to cool off and the coolant within the system will boil. The engine will overheat among these other symptoms.

Symptoms Of A Broken Serpentine Belt

  • Decreased power to the electrical system
  • Loss of power assist in the steering system
  • Engine overheating due to lack of coolant circulation
  • Alternator not generating power
  • Dead battery
  • Dimmed lights
  • Non working radio


What Is A Radiator And How It Works

The radiator is the part of your cooling system where the hot engine coolant goes to cool off. The radiator is made out of thin piping which the coolant courses through after coming out of the engine block. The small metal piping does a great job of giving the coolant a lot of surface area in a casing that transfers heat well. Your car then uses airflow provided by the moving car and the cooling fan to remove heat from the coolant.

When the coolant is effectively cooled it is sent back through the engine to bring down engine temperatures.

Issues You May Be Having With Your Radiator

Usually the two issues you will have with your radiator is it is either leaking or there are clogs in the radiator which are slowing the flow of coolant or preventing it all together. Disruptions in the flow of coolant 

Signs That Your Radiator Is Failing

  1. Your vehicle is overheating 
  2. Your vehicle is leaking coolant
  3. You have sludge built up in your radiator. 
  4. You may be displaying low coolant levels when you think you shouldn’t be. 

Broken Heater Core

A common cause of overheating  is that your heater core is malfunctioning. Heater cores are responsible for defrosting functions and transference of the heat within the cooling system to the passenger compartment of a car.

A heater core is an extension of your radiator which is made of metal piping usually aluminum or brass. This thin piping carries the  hot engine coolant. Helping to drop the temperature of the scalding liquid to a level where it can be run back through the engine block again. Heater cores look a lot like a small radiator if you are trying to draw a mental map. 

If the heater core in your vehicle is not working properly you will not have heat in your vehicle which while simply discomforting in most situations, is not the bigger issue. A common issue with heater core units is leaking and reduced pressure which will lead to the overheating you are experiencing. Check your heater core’s health by noticing these tell signs

  •  The fogging up of your windshield 
  • Your car is overheating
  • You are burning through engine coolant at an abnormally fast pace
  • You notice a fruity or sweet smell inside your car

Airflow Blockage

Why You Need Airflow To Cool Your Car

The radiator, as we discussed, needs airflow to help remove heat from the hot engine coolant. Your car uses a combination of air from the moving car and air blown onto the radiator by the cooling fan. When this air flow is blocked, the coolant isn’t able to properly cool off before being exposed to more heat. If the problem is severe enough, the coolant will boil and the engine will overheat.

The grate on the front of your car is the main intake area for airflow, in some cases the grate can become so lodged with junk like leaves, pollen, dirt etc. that it becomes too clogged to allow the air to pass.

Signs That Your Cooling System Isn’t Getting Enough Airflow

  • The car is overheating
  • While the integrity of the coolant is good, the coolant is still boiling

Cooling Fan

What The Cooling Fan Does For You Cooling System

The job of a radiator fan is to pull air across the radiator and cool the coolant at an accelerated rate. Your vehicle does also use natural airflow from the moving vehicle to accomplish this task as well. Without proper ventilation, the engine coolant will not reduce in temperature as quickly and will lead to increased engine temps. 

Signs That You Have A Bad Radiator Fan

  1. Your engine is overheating when your vehicle is stopped for extended periods. 
  2. Your engine is running slightly hot
  3. Warning lights are on
  4. Your air conditioning is blowing hot air


The Job Of The Fuse

The job of the fuse is relatively consistent throughout all the fuses in your car. Fuses are there to protect the wiring in in your car. There are typically 2 fuse boxes in a car, one in the engine block and another in the cab of the car. The fuse box within the engine compartment holds the fuses for the cooling fans and other electrical components.

Reasons A Bad Fuse Could Be Your Issue

A blown fuse will not allow power to be provided through the electrical components. The cooling fan will not work if the fuse is not in working condition.

Symptoms Of A Bad Fuse In Your Cooling System

  1. You will not have a working cooling fan
  2. Your engine is overheating when your vehicle is stopped for extended periods. 
  3. Your engine is running slightly hot
  4. Warning lights are on
  5. Your air conditioning is blowing hot air

Coolant Integrity

What Coolant Does

Your car uses coolant to keep your engine block from overheating. Engine coolant is typically a mix of 50% antifreeze and 50% water. Engine coolant has a tough job to do based simply on the job description alone. Your engine gets HOT thanks to the controlled gasoline explosions propelling the car forward. 

The burning of gasoline takes place around 495 degrees F. The engine block itself won’t get quite that hot, but engine coolant still has to have a very high boiling point, much higher than water alone at 223 degrees F.  This is because once a liquid is boiling it cannot receive any more heat so if your engine coolant starts to boil, it can’t do its job. Engine coolant must also have a very low freezing point (you do not want the cooling system in your car to freeze). 

Why Coolant Could Still Be Your Issue Despite Proper Volume

You may be using the correct coolant in your car and it may be wearing down or you may have the wrong type of coolant altogether. Either way you’ll need to drain the reservoir, flush it, and refill with the proper engine coolant. 

If your coolant is still relatively full I would check the integrity of the solution. Antifreeze does wear down eventually and becomes incapable of doing its job properly.

Symptoms Of Bad Engine Coolant

Tell signs that your coolant needs to be replaced include discoloration, thick or sludge like appearance,  a sweet smell inside your car, or your car is overheating. 

How Do I Stop My Coolant From Overheating

Your coolant could be overheating because you have an airflow issue, but it could also be overheating if the coolant is old and need replacing. Additionally, coolant can overheat if it is not being effectively pushed through the cooling system.

So How Hot Is Too Hot For A Vehicle?

Any car reaching 230 degrees F and over is considered to be overheated. At this temperature engine parts begin to not be able to withstand the temperatures and will start to warp and melt.

The cooling system is responsible for keeping the engine temperatures of your car at a low enough level that the mechanical parts won’t melt. Gasoline fires burn at 1733 degrees F and the optimal car temperature is around 200 degrees. A car without a proper cooling system can reach up to 400 degrees F which can do some serious damage to a vehicle likely totaling it.

Is It Safe To Drive An Overheating Car?

If you’re asking whether your car will still run despite running hot it will. If you want to know if it is advisable whether or not to drive the car the answer is no, this is a really, really bad idea. If you make the decision to drive your vehicle, knowing it is overheating, you are looking at taking your repair costs from $10- $400 to well above the $2000 mark. When your engine severely overheats, your engine parts will warp. 

Common Repairs After Engine Overheating

If you decide to drive your vehicle knowing well that it is overheating, you can expect to pay a lot in repairs when your internal parts of your engine block begin to warp. Engine overheating causes warping of several important components of the engine like the aluminum cylinders, engine head gasket and water pump. 

Common parts that break and require repairs after engine overheating include a cracked head gasket (average replacement cost $1500), warped cylinders (average replacement cost $500) and water pump replacement ($350- $700).

As you can see, repairs for blown head gaskets and warped engine parts are expensive and no warranty will cover repairs caused by negligent maintenance. 

How To Deal With An Overheating Car

Here is what you should do immediately to mitigate the damaging effects of an engine overheating. 

  1. Turn off the air conditioning and turn the heat on high.
  2. Turn on your defroster and blast the heat at full fan volume.
  3. Roll down the windows to help let out some of the heat.
  4. If you are in traffic, put your car in neutral or park wherever it is safe to do so as you try to get off the road.
  5. Drop your car into the lowest gear and try to use as little acceleration as possible as you try to get off the road and find a safe place to stop. 
  6. Call a tow truck OR wait for your vehicle to cool off (COMPLETELY) and check your fluid levels. 

If you notice your car is overheating, the best thing that you can do is try to remove as much of the heat as possible from the engine block to mitigate the damages. By using your heater, which is a component of your cooling system, you can redirect some of that heat from your heater core into the cab of your vehicle. Do the same thing with your defroster and take as much heat as possible away from the coolant in your cooling system. 

If it’s a summer month, you’re going to be uncomfortable sitting in your hot car, but trust me when I tell you that it is better than the alternative which is spending THOUSANDS of dollars on repairs when your engine has a full-on meltdown. 

By putting your car in as low of gear as possible and minimizing your acceleration you are essentially minimizing the amount of heat that you are adding into an already overheating engine block. 

When you notice that your car is overheating, do your best to get to a stopping point as soon as possible. You want to pick a safe place because odds are you’re going to be there for a while, but where you stop and how much further you drive is up to you. Remember that even driving just a little further can cause a pricey component of your engine to break. Use your best judgment to keep yourself safe and your car from having even more damage. 

If you are on the interstate, and there is an exit coming up, take it and find a parking lot or gas station. If you are driving at night, find a well-lit area if at all possible. TURN OFF YOUR CAR AS SOON AS POSSIBLE. Even running in idle will burn fuel and add heat to your engine block. 

Now you’re going to want to do one of two things, call a tow truck, or wait for your car to cool down to the point that you can open your hood and check your fluids. In some cases, you are simply in need of engine coolant, and if you haven’t topped off your coolant levels in some time you may have an easy fix on your hands. 

If you suspect this is the issue, lock up your car and get a ride to your nearest engine part store or large retailer to get some engine coolant. Before you go, be sure to check your owners manual to determine what type of coolant your car takes. When you get back to your car, it should be completely cool but double-check the temperatures before ever opening any of your fluid compartments. 

If you are diligent about ensuring your fluid levels in your vehicle are topped off, you probably have a more serious repair on your hands and you are going to need a tow truck. Remember you should never drive a car that is overheating. Have your car towed to your home or to a mechanic you trust in the area.

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