Why Is My Car Overheating

by | Sep 20, 2020

You’re driving down the road, and to your dismay, you notice the thermostat on your dashboard is reading out H for HOT HOT HOT instead of sitting comfortably at a normal operating temperature. We all hate when our car breaks down. Between the fear of being stranded, knowing that you could be facing a costly repair, and the overall inconvenience to our day, it just really sucks. 

Well, the best way to make the most of a bad situation is to be informed and take the necessary steps to improve your situation. You need to do something about it and you need to do it fast. If you’re just reading this to be prepared, good job for being proactive!  If your car is currently overheating follow the next section below to get yourself to a safe location and avoid damaging your engine block. 

What To Do When Your Car Overheats 

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.

How Does The Cooling System In My Vehicle Work?

Before we get into what components of your engine are likely causing your car to overheat, you should have at least a basic understanding of how the standard coolant system works in a vehicle. Luckily for the simplicity of this lesson,  there is little to no variation in this across vehicles. 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. At this point, it 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 uses airflow created by your moving vehicle to quickly remove heat. 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.  Once fully cooled, the engine coolant is recycled and put back into 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 

Cars burn gas the most effectively, at a certain temperature, so they want the engine block to achieve this temperature as quickly as possible.

The 10 Most Common Causes Of Engine Overheating

  • Low levels of engine coolant
  • Leaking coolant system
  • Coolant Concentration
  • Bad Thermostat
  • Issues With Radiator
  • Leaking Hoses
  • Bad Radiator Fan
  • Broken Water Pump
  • Broken Water Pump Belt
  • Cracked Heater Core
  • Engine Coolant

The most simple fix (and dumb car owner move) is when your car overheats due to lack of fluids. Engine coolant, which is a mixture of antifreeze and water, is the fluid that is pumped through your scalding engine block to keep it at safe operating temperatures. Here is how that works:

A Bit About Engine Coolant

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). 

You might think frozen coolant would be highly effective, but unfortunately, that is inaccurate. Should the fluid freeze, it won’t circulate until it melts and at that point, you could have a ton of damage to your engine block in the areas that don’t have frozen coolant. The coolant can also expand when it freezes and may bust whatever hose or component is housing it. 

Why It Is Important To Maintain Safe Levels Of Engine Coolant

As we discussed above, engine coolant must be present to prevent an engine from running too hot. If you have no engine coolant or very little engine coolant you will subject your car to overheating. Luckily this is a very easy fix. 

How To Know If You Don’t Have Enough Coolant

  1. Your car is overheating (which is why we’re here)
  2. The heat in your car isn’t working
  3. Check the levels in your coolant reservoir 

The Heat Is Not Working Explained

Generally when you don’t have enough coolant, your engine overheating is not the first sign. Part of your radiator (and cooling system) is your heater core which is essentially a mini radiator that provides heat to the cab of your car. Your car may have enough coolant to maintain proper driving temperatures within your engine but may not have the quantity necessary to reach all the way into your heater core. 

Checking Your Engine Coolant

CAUTION: REMEMBER TO NEVER MESS WITH FLUID COMPARTMENTS IN YOUR ENGINE BLOCK WHEN YOUR CAR IS HOT. 

This is definitely an issue as we’ve previously discussed which can lead to expensive repairs in the future and should be addressed immediately if found to be the cause of your overheating car. While this issue is serious, it is also the easiest to fix. You’ll want to pop the hood of the vehicle and locate the coolant compartment. In most vehicles you will find the fluid compartment on the upper left hand side while standing in front of your car. The compartment will be transparent and have a cap on it.  You should be able to see the fill line without even opening it. 

If your reservoir is low, it is really easy to fill it up. You will want to use an antifreeze solution here using purified water, or a premixed engine coolant from the store depending on manufacturer instructions. You can find the proper coolant for your car detailed in your owner’s manual and the coolant you need will almost always be sold at auto part stores or large retailers that have an automotive department like Walmart or Target. 

Again, make sure your engine is cooled completely before you go anywhere near this reservoir. The engine coolant is hot inside a running engine and can become pressurized. No one wants 220 degree coolant blowing up in your face. 

Leaking Coolant System

Leaks in the coolant system are the number one reason that vehicles overheat. As we’ve described above, the cooling system is vital to keeping your vehicle from overheating. There are a lot of components to the cooling system and any one of them could be your culprit. 

Look for these tell signs that you have a leak in your cooling system

  • Your car is visibly leaking fluid (be sure to clean up after your vehicle if you have a coolant leak because antifreeze is toxic not just to people and children but to animals and plants as well)
  • You recently filled up your coolant reservoir and it is already in need of more coolant. In this scenario where you are not visibly seeing a loss of coolant on the ground you have a less severe leak on your hands, but a leak nonetheless. 

Parts Of Your Cooling System That Could Be Leaking

There are many components that make up your vehicle’s cooling system and any one of them can be your issue. 

  1. Hoses
  2. Radiator
  3. Water pump
  4. Thermostat housing 
  5. Heater core 
  6. Head gasket
  7. Freeze plugs

If you have a leak, even a small one, get it repaired immediately. You are leaking dangerous chemicals into the road which are then being washed into local waterways! Also you could be setting yourself up for a more costly repair by waiting. 

Coolant Concentration

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. 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 To Safely And Effectively Drain And Flush Your Cooling System

If you are actively trying to flush your cooling system yourself, way to go! This is awesome. It is great to know how to do these maintenance items on your car yourself and it can save you a ton of money over the years if you continue to replace it at home. With that being said it is important to make sure you are replacing the fluid properly and especially that you dispose of your old coolant in a responsible fashion which we will discuss in detail below. 

I’ve included a YouTube video which goes into detail on the process of draining, flushing and replacing the coolant in your cooling system. In the video you will find helpful information regarding. 

  • Safety. Both in opening the coolant reservoir, safe handling and removal of coolant and what to do with the coolant after you’ve finished the job. Remember to never open your coolant reservoir when your car has been running. Hot coolant can become pressurized and blow up in your face if you do not let the engine cool appropriately. Take some extra time to make yourself comfortable with the safety warnings he gives you. 
  • Preparations: There are a few steps in the flushing process that can take a couple of days, so don’t expect to get this done all in one day. Pick a weekend where you have the time to do this right. He’ll also discuss what you’ll need to have ready to go to get started.
  • Where in your owner’s manual you can look to find the information you need regarding the actual concentration of coolant your specific car takes
  • Hoses: W\here they are located. How to disconnect. How to reconnect. Using hoses to flush the system. 
  • Draining: How to ensure you’ve drained the old coolant entirely. What you should drain coolant into. 
  • Flushing: How many flushes you’ll need to make. 
  • Handling of coolant: How to properly handle and dispose of used engine coolant.
  • Replacement: This part is pretty simple, but he shows you how to replace your coolant and seal your reservoir at the end of the video. 

What Should I Do With My Old Engine Coolant After I Removed It From My Car? 

When you remove and replace your engine coolant yourself you want to use extreme caution in making sure the coolant is handled and disposed of properly. Antifreeze is toxic and should not simply be dumped out with the trash or down the drain. 

Coolant needs to be disposed of properly. You can do this by transferring the liquid into something watertight and a size that is feasible for transport as you will be taking it in for recycling. 

It is a relatively simple process to get rid of old engine coolant. You can take it to most mechanics and they will gladly take it off of your hands. They are gracious in this aspect not because they are kind hearted people, but because they make money when they sell the coolant off to a disposal company who reworks the materials. You can also contact the disposal company directly to sell yours, though with the small quantity you’ll have, I’m not sure it is worth your time. 

You can also recycle the fluid at your local disposal center or hire a private waste disposal company to come pick it up from you. 

I want to reiterate here that engine coolant is toxic. We do not want it in our water systems, in our pets or in our children. Be responsible. 

Bad Thermostat

The thermostat controls the valve that allows the engine coolant to flow from the radiator into the engine block and circulate from there. 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. 

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

Issues With 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 are displaying low coolant levels when you think you shouldn’t be. 

Leaking Hoses

Another common reason your car is overheating would be loss of fluid due to leaking hoses. Your water pump can’t circulate coolant if it has all leaked out. Hoses, as they age, can crack as the rubber oxidizes. Sometimes hoses can get holes in them due to pests or other unfortunate circumstances at no fault of the owner. As a rule of thumb the hoses in your engine block should be replaced every 4 years. 

Bad Radiator Fan

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

Broken Water Pump

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

Cost Of Replacement

How much you spend on replacing a water pump is going to vary based on who you have do the deed (aka what mechanic you use) and what type of car you own. 

The type of car is not as important for actual part cost, the water pump itself typically costs between $50 and $100. The real cost associated with replacing a water pump is the labor hours which is why it is really important to choose the right mechanic. Overall costs of replacing this part are between $300 and $750. Most of this cost as you can see are in labor hours and this is because the water pump tends to be hidden and not easily accessible for removal and replacement. 

 The water pump on a vehicle needs to be replaced every 60,000 to 90,000 miles which is the same timeframe as the timing belt (see below). In some vehicles the water pump is behind the timing cover, making it logical to replace these parts at the same time and the part is again pretty cheap for the timing belt as well. 

Broken Water Pump Belt

Similar to the water pump, the water pump belt is responsible for controlling 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 water pump belt:

  • Breaking 
  • Loose/ Worn out

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 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 which will lead to the overheating you are experiencing. This will lead to insufficient coolant levels. 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

Frequently Asked Questions:

How Do You Stop Your Car From Overheating?

You can prevent your car from overheating by identifying what is causing the issue involving your cooling system and making repairs. Usually the common parts that are responsible for engine overheating include: insufficient or old coolant, broken or cracked hoses, leaking or clogged radiator, broken heater core, bad water pump or water pump belt. 

My Car Is Overheating, Can I Still Drive It? 

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. 

What Happens If You Keep Driving A Car That Is 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. 

Symptoms Of A Blown Head Gasket

The head gasket is responsible for sealing the cylinders preventing coolant and oil from leaking into them. The head gasket has an incredible job as both sides of the engine block expand, shrink, warp and rub together and the head gasket withstands all of it. 

Symptoms of a blown head gasket include:

  1. White smoke coming from the tailpipe
  2. Water leaking from the tailpipe
  3. Milky white coloration in the oil
  4. Bubbling in the coolant reservoir or in the radiator
  5. And of course, engine overheating 

Is A Blown Head Gasket Worth Replacing? 

It depends. If your car isn’t worth very much then your answer is probably no. A blown head gasket on average is going to cost around $1500 to replace. If your car holds sentimental value to you then your situation may be different. 

If your car isn’t worth a ton itself, but is relatively low mileage and you think will last you a while, it may be cheaper to replace the head gasket and get the remaining years of life out of your existing vehicle. 

How Much Is My Overheating Car Going To Cost Me To Repair?

This is going to vary depending on your problem. Replacing the coolant in your vehicle won’t cost you more than $20 but if you have a bad water pump that needs replacing it’s going to cost you upwards of $800. If you don’t let your car severely overheat this is probably the most that you will pay. 

If your car was still driven and you now have warped engine parts on your hands, it’s going to cost you anywhere from $500 to $2700 depending on what broke in the process. If you have a cracked head gasket expect to pay at least $1500. And no your warranty is not going to cover these issues because they resulted from negligent maintenance or driving decisions. 

My Car Is Running Hot, But Isn’t Overheating. Help!

Usually when your car is running just slightly hot it is an indication that you don’t have enough coolant circulating or the coolant is not being cooled properly. You’ll want to take the vehicle to a mechanic for diagnosing if you aren’t a car person, which you probably aren’t if you’re asking this question. 

Typically a car running slightly hot is in the process of getting to a level where the car will overheat. Whether you have a slow leak or a slight clog in the radiator, it’s probably a sign of bad things to come. Get your car to the mechanic as soon as possible and avoid driving long distances until you do. 

Why Is My Car Overheating In The Cold

Your car runs very very hot. Hot enough that cold temperatures outside are going to do very little to cool it off. Honestly outside temperatures shouldn’t even be a factor in your mind when it comes to the cooling system in your vehicle. Yes, cars can have a harder time staying cool when it is hot outside. 

Your car is experiencing internal combustion temperatures of almost 500 degrees. A little cold weather isn’t going to do much for you in terms of cooling off the engine block. If your car is overheating in winter it is likely because you don’t have sufficient cooling levels, you have a clogged radiator, issues with the water pump or belt, have a leak in your cooling system or you have a bad thermometer. 

Can Low Oil Cause Overheating?

Yes, low oil levels or a clogged oil filter can cause your vehicle to overheat. The oil is meant to lubricate engine parts and reduce friction and in doing this reduction of overall heat. If your car takes 5 quarts of oil and you are currently operating with 4, you are only reducing friction by about 80% of what you should be. 

Clogged oil filters are another cause of engine overheating. An oil filter is there to keep foreign particles like dirt, glass, and paint chips out of your engine block. With time the filter will remove so many foreign particles that it can become clogged, reducing the amount of oil that can get through. In some severe cases, a clogged filter can cut off the supply of oil entirely. 

Be sure to keep your oil topped off at all times. Both your oil and oil filter do need to be replaced over time. Time frames will vary depending on the variety of oil that your vehicle takes, the same goes for the oil filter, but as a general rule of thumb replace these every 3,000 miles. With advances in technology, some oils and filters can last between 8,000 and 10,000 miles again you should check your specific products for maintenance information. 

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References:

https://www.military.com/off-duty/autos/auto-repair-overcoming-overheating.html
https://www.aaa.com/autorepair/articles/how-often-should-you-change-engine-oil#:~:text=It%20used%20to%20be%20normal,as%2015%2C000%20miles%20between%20services!
https://eliteautorepairtempe.com/my-car-is-overheating-what-could-be-wrong-what-do-i-do/
https://www.lifewire.com/when-your-heater-blows-cold-air-534667
https://www.subarusuperstorewest.com/service/learning/learn-why-your-vehicle-heater-air-conditioning-stopped-working-surprise-az.htm
http://www.ace-autoparts.com/About/Blog/entryid/13/four-signs-you-have-a-bad-or-failing-radiator
https://www.autoblog.com/2019/06/13/symptoms-of-a-bad-or-failing-thermostat/
https://www.yourmechanic.com/article/how-often-should-hoses-be-replaced#:~:text=Most%20automakers%20and%20belt%20manufacturers,the%20hoses%20replaced%20much%20sooner.
http://www.ace-autoparts.com/About/Blog/entryid/13/four-signs-you-have-a-bad-or-failing-radiator
https://www.felpro.com/gaskets-101/signs-of-a-blown-head-gasket.html

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