Does Engine Coolant Go Bad?


The cooling system is a vital part of keeping your car at safe and operable temperatures. The cooling system cannot function without all parts functioning properly, most important and the star of the show, engine coolant. Engine coolant is a chemical compound made of antifreeze, and water. Over time the compound will break down and go bad as it is run through your vehicle.

Pure antifreeze that has not been used (is still in the bottle) has an almost infinite shelf life while it sits in its original air tight container. Pre mixed engine coolant which is a mixture of antifreeze and water does have a shelf life which will vary from brand to brand. The range for shelf life for a pre-mixed engine coolant is anywhere from 1 to 5 years.

Coolant or Antifreeze? What Is The Difference?

It seems everyone tosses around the phrases coolant and antifreeze as if the two are interchangeable. This is true to an extent but the two are different things and shouldn’t be misused. Let’s shed some light on the differences between the two words.

What Is Engine Coolant?

Engine coolant is the liquid that runs from your engine block to your radiator removing heat and keeping the car at an operable temperature. Engine coolant, true to its name cools the engine, but how does it do this?

Engine coolant is a solution. Meaning it is made up of a mix of several substances. One of those substances is called antifreeze.

What Is Antifreeze?

Antifreeze is a chemical, ethylene glycol, which is found in most premixed engine coolants that are ready to be added to your vehicle.

Ethylene glycol is also sold separately as a pure substance ready to be mixed with softened water and then funneled into your car’s cooling system (after you have read the manufacturer’s instructions and safety warnings).

What Does Antifreeze Do For Our Vehicles

  1. Water is corrosive! Pure water inside our cooling system and will eventually corrode the radiator and cause rusting of the internal components it comes in contact with making them unable to do their job. Antifreeze is an anti corrosive substance that prevents the water from reacting and stripping the metal.
  2. Water has a relatively low freezing point, but in most areas of the world winter does get cold enough to bring fresh water to a solid ice. If this was to happen within a vehicle it would break the engine. Anti freeze significantly lowers the freezing point of water.
  3. Coolant also keeps the water from boiling when it gets too hot. When engine coolant boils, or any other liquid for that matter it cannot get any hotter while in the liquid form. What this means is that it is no longer effective at receiving heat from your engine or cooling anything down. Antifreeze raises the boiling point of the water.
  4. Antifreeze also protects your car’s cooling system when driving in extreme weather climates. So if you’re planning on adventuring towards the poles in your vehicle or driving through death valley you should make sure your cars coolant levels are full and have been mixed with the appropriate coolant for your vehicle and the driving conditions.

What Are My Options For Engine Coolant

You have 2 options for engine coolant

  • Mix your own using pure antifreeze
  • Buy pre-mixed engine coolant

Your options are to purchase a premixed engine coolant that is ready to be added to your empty, clean, engine coolant compartment in your car. Or you can purchase anti-freeze and mix a 1:1 ratio with softened water. Always read the mixing instructions to verify safety procedures and mixing ratios which may vary from brand to brand.

I have included some information further along in this article to help you clean out your engine coolant system of all old, used and dirty coolant and to help you dispose of it properly.

REMEMBER antifreeze is toxic and has to be disposed of properly! Please be sure to keep your used and replacement coolant away from animals it tastes sweet to them and they will drink it.

Does Engine Coolant Go Bad While In The Bottle?

Pre mixed engine coolant does have a shelf life of somewhere between 1 and 5 years depending on the brand that you select. Each bottle of engine coolant will have an expiration date listed on it. Pure antifreeze has a much longer shelf life, almost infinite if stored properly.

Read manufacturer storing instructions and expiration dates to ensure your engine coolant is still good.

Does Engine Coolant Go Bad In Your Car?

Engine coolant in your vehicle will definitely go bad and need to be replaced every 30,000 miles or so. Older fluid can become contaminated with metal pieces from your cooling system or may cause acid build up in the radiator.

When coolant goes bad, it may have a reduced boiling point making it less effective at cooling your vehicle. If the boiling point drops too low the coolant will boil within your cooling system wreaking havoc and causing the car to overheat. It is imperative that the coolant is regularly checked and maintained.

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 Degraded Coolant Could Cause Your Car To Overheat

If your car is overheating and you have the proper levels of coolant, 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. We’ve included details on how to do this in a section below.

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

Signs that your coolant needs to be replaced include physical discoloration, thick or sludge like appearance,  a sweet smell inside your car, and your car overheating. 

How Do I Stop My Coolant From Overheating

You may have an airflow issue in your car that is blocking the radiator from getting the cooling air that it needs to reduce the temperature of the coolant. Check your car for bad filters and blockages due to leaves and debris in the front grill. The other issue is that you may have old or bad coolant in your system that has suffered from antifreeze deterioration. Finally, there may be a circulation issue in the cooling system which generally points to an issue with the water pump.

Change The Fluids In Your Cooling System Every 30,000 Miles

Eventually the chemicals in antifreeze will breakdown and become less effective at keeping your car’s temperatures in a safe range. When this happens your car is at a high risk of engine overheating which can lead to costly repairs.

Its best to be proactive here and change this antifreeze combination every 30,000 miles or so for most vehicles. Your car’s user manual should make a recommendation on this mileage specific to your vehicle in the same section where they detail what

Make Sure You Dispose Of Your Antifreeze Properly

Be careful with your used engine fluid during the removal process!! It is toxic and should be handled appropriately. You cannot simply dump it out with the trash or down a drain. It needs to be disposed of properly and safely. Follow these steps to keep yourself, family, pets, and the environment and wildlife around you safe from chemical harm.

Transfer the liquid into something watertight. It needs to be in a container that will be feasible to put in your car to take in for recycling. Used engine coolant can be properly disposed of pretty easily. Most mechanics will take it off your hands for free (they make money when they sell it off to the disposal companies).

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 reiterate here, engine coolant is toxic. We do not want it in our water systems, in our pets or in our children. That would be bad. Be responsible.

Does Engine Coolant Evaporate?

Yes, engine coolant does evaporate over time from the coolant reservoir. However, this will be the smallest amount and should not lead to a shortage of coolant. If you are losing a significant amount of coolant in a short period of time you likely have a leak in your cooling system or a radiator cap that is not maintaining pressure.

DIY Drain And Flush Your Cooling System

Most of my readers are interested in engine coolant because they are actively undertaking the replacement of their engine coolant themselves. This is awesome and will save you guys some money, however you need to make sure you are replacing the fluid properly and especially that you dispose of your old coolant in a responsible fashion.

  1. SAFETY. Cooling systems are pressurized and you need to ensure you are using your car when the engine is cool. We don’t want you to get scalded by super hot engine coolant, okay? Please pay attention to these warnings he gives you.
  2. What preparations you need to make before flushing your engine’s cooling system. Generally it is suggested that you use a chemical coolant flush several days before actually flushing your engine.
  3. The section in which you can look within your owners manual for information regarding what engine coolant you should personally use for your car.
  4. How to disconnect and reconnect the hoses in your cars cooling system so that you can attach a hose and flush the system.
  5. How to ensure the engine cooling system has been drained entirely.
  6. What to drain your old cooling fluid into.
  7. Safe handling and disposal of used engine coolant.
  8. He even shows you the change in color with each of his five or so engine flushes!
  9. Finally, the video shows him replacing the engine coolant with new coolant.

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Protect My Car is an extended auto warranty company. Our goal here at Protect My Car is to eliminate your worry of being financially responsible for an expensive mechanical breakdown. With our extended auto warranty, you don’t have to worry about being fully burdened with the cost of a covered repair.