What is antifreeze? And how to check your engine coolant level

Auto Express explains how antifreeze keeps your engine from overheating and why you should check your levels

As the name suggests, the primary function of antifreeze is to stop your car’s coolant freezing (with coolant being a combination of water and antifreeze). Everything from your standard variety Ford Fiesta, to premium cars like the Jaguar F-Type relies on this liquid, but to understand what it is, we need to know what it does.

There are channels inside an engine which allow coolant to circulate, removing excess heat from the engine block. The heated mixture is then taken via connecting pipes to a radiator, where heat is removed from the fluid. It is then pumped back into the engine to begin the whole process again.

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The problem is, when you turn your engine off, the fluid stops moving and the engine begins to cool. It’s especially important to keep an eye on your coolant if you live somewhere where temperatures drop below freezing. If the water in the coolant channels freezes, it can expand and cause stress on the engine block. The knock on effects of which can result in a wide range of problems, including coolant leaks or even a warped cylinder head.

On top of lowering the freezing point of the mixture, antifreeze also serves another purpose – it acts as a lubricant/projector for the engine internals. Most engines are made from either iron, or aluminium, both materials which can be eroded by water. Therefore, modern antifreeze coolant contains chemicals which protect the internals of and engine from corrosion – including the water pump, which is often located in awkward places that make repairs expensive.

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How do you check your car’s coolant level?

Well, there are two common ways to do this, and it depends on the cooling system your car has. Firstly, there are systems which have a coolant reservoir allowing the coolant level to change as the system heats up without dumping fluid. To check the level of a system like this, follow the steps below:

Check engine coolant on cars with a reservoir

  • 1. Let the engine cool completely as the system becomes pressurised under use.
  • 2. Use your handbook to locate the position of the coolant reservoir in the engine bay.
  • 3. Open the bonnet and locate the coolant reservoir, if you do not have the hand book, it is normally on one side of the engine over a wheel arch.
  • 4. On one side of the reservoir there will be a minimum and maximum mark to indicate where the level of the coolant should be (these are usually for when the coolant is cool), use these to check the level of the fluid.
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    Check engine coolant on cars without a reservoir

    There are also systems which do not have a reservoir. They may have an overflow tank where water can be released to, but it cannot return to the engine.

  • 1. Similar to above, let the engine cool completely as the system becomes pressurised under use.
  • 2. Open the bonnet and locate the radiator – it is usually at the front of the engine. If you cannot find it, fall back to the car’s handbook for instructions.
  • 3. Get a rag or old tea towel and carefully undo the cap on top of the radiator. If you have not waited long enough for the engine to cool, steam may be released, so be careful.
  • 4. With the cap removed, look into the radiator, the coolant should be up to the top.
  • If, after checking coolant level of your car it is below the minimum, you will either need to top it up, or even better, drain the system and replace the coolant. A mechanic will be more than happy to replace your engine coolant for you.

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    If you decide to do the work yourself, there are a couple of things to bear in mind. Firstly, most modern cars have completely sealed systems, meaning coolant should only need replacing if there has been a leak, so it may be worth investigating that sooner rather than later or the problem may continue to get worse. Also, the different types of antifreeze do no mix and can have adverse effects on your car, so make sure you get the correct one. 

    Have you had any coolng related horror stories? Let us know in the comments below…

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