When it comes to renewing the engine coolant, there isn't a great deal that can go wrong. As long as you can access and undo either the drain plug (if fitted) or the lower radiator hose then draining the system is a matter of placing a large receptacle under the drainage point and allowing the coolant to empty into it.
Make sure the coolant isn't hot, and that you've got a big enough container – It's likely to splash everywhere so be prepared to deal with the resultant mess. The main problem you're likely to face comes when you add the new coolant.
It's easy to get an air lock – which can cause problems with overheating. To minimise the risk of this happening always ensure the heater controls in the car are set to 'hot' and periodically give the main (largest) radiator hoses a squeeze as you're filling it with fresh coolant.
Once filled run the engine until the fan comes on, and check the level again – it's likely to have dropped fairly substantially once it's circulated around the whole engine.
What tools you'll need to replace coolant
Replacing the coolant is a simple procedure, and requires very little in the way of tools. Depending on how your coolant drains, you will either have to undo a drain plug (usually with a small socket) or possibly remove the hose entering the bottom of the radiator.
These will be held on with a hose clip. If you're lucky they will be screw-threaded jubilee clips, and a simple screwdriver will remove them. They may be the type that requires hose clip clamps (or you could attempt it with some long-nosed pliers).
These are easy to operate with the correct tool, and make refitting the clamp easy. If you have ear crimp hoses then you will need to cut the clamp off – side cutters are best for this – and a new clamp needs to be refitted.
We'd recommend fitting a jubilee clip of the correct diameter if you don't have hose clamp crimper.
How to extend the life of your engine coolant
It's never wise to attempt to extend the life of engine coolant. As it ages it is less effective at resisting internal engine corrosion, and it can become less effecting at cooling, and resisting freezing. Nor should you add the wrong type of coolant to 'top it up'. Mixing the coolants can dramatically reduce their effectiveness, and even make the fluid more viscous and sludgy.
How long should engine coolant last?
How long it should last depends on the type of coolant you have in your vehicle. IAT uses silicates and phosphates as corrosion inhibitors and it should ideally be flushed and replaced every two years.
The additives in OAT fluid are more effective than those found in IAT and generally a service interval of 5 years is acceptable between flushes. HOAT has the same life expectancy as OAT.
How much does it cost to replace coolant yourself?
Presuming you already have the correct tools to loosen the hose clamps, and a suitable catch tank, the only cost will be for the coolant itself. This will usually cost between £20 and £40 depending on the type and brand. Always stick with the manufacturers recommendation.