How an engine’s cooling system works

Coolant Replacment Image

Coolant is your engine’s lifeblood. The fluid keeps the motor at the correct operating temperature, helping it to warm up quickly in cold weather and not get too hot when under stress – and when mixed with the correct antifreeze it prevents damage in cold weather and stops corrosion (so always add it, even if you don’t live in a cold climate).

Take a look at your car’s handbook for coolant change intervals. Some models need a change every couple of years but some can go for longer.

This task is reasonably easy and requires only basic tools. It should take between 1-2 hours.

What is the lifespan of your engine coolant?

Coolant is deeply important. It’s the liquid tasked with coursing through your engine to keep it cool and happy. It also works its way through the interior heater matrix to keep the cabin warm.

Without it, you would be very cold indeed, but your engine would be very, very hot. And given this, you’d think that servicing it would be pretty important, right? Well, evidently not.

Some people will tell you that it needs to be changed every year, some will say longer. Some manufacturers say you don’t have to change it for 150,000 miles (looking at you, Mercedes-Benz) which seems brave to us.

Changing the coolant is not a big job, and as such, we would advise changing it seasonally, or twice a year to be more exact. It might seem like a lot, but trust us, there is a method to our reasoning.

Coolant is seasonal

Your engine needs coolant. You should never, ever just put water in your cooling system. Water on its own will course through your engine and do nothing but aid to corrosion. Plus, water is volatile and unpredictable. The coolant additive you put into your engine is chemically balanced to react in certain ways under certain conditions.

Take winter coolant. The operational range of the coolant is shifted to account for the lower temperatures, this means it is more stable and can more effectively cool the engine. It also means it won’t freeze, which is exactly what water will do. And when water freezes in your engine block, it will crack it. And that’s game over.

Summer coolant works better in higher temperatures, meaning it is chemically engineered to not work as hard as plain water would have to in high temperatures. For example, you could have plain water in your car, yes? Sit in traffic on a hot day and even with a healthy, full cooling system, the water is going to get excessively hot, resulting it boiling. Summer coolant has a higher boiling point, so it won’t do this.

With that in mind, we would change the coolant seasonally. Most cars have a bleed screw on the radiator, but even if they don’t it’s only a case of removing a lower hose to drain the system. Your Haynes guide will tell you all you need to know about draining the system of your car.

When to change your coolant

“If you can’t remember the last time the coolant was changed, change it now”

Always consult your vehicle’s handbook for recommended intervals, but we think that two years is a suitable period. If you can’t remember the last time the coolant was changed, and it’s looking cloudy and discoloured, change it now. Part of the cooling system service involves flushing. If the coolant is changed on a regular basis you may need to flush only once before refilling.

Always wait until the coolant is cold before draining it. Don’t allow antifreeze to come in contact with your skin or painted surfaces of the vehicle and rinse off spills immediately with plenty of water. Never leave antifreeze lying around in an open container or in puddles on the floor; children and pets are attracted by its sweet smell and may drink it.

Check with local authorities about disposing of used antifreeze. Many communities have collection centres which will dispose of antifreeze safely. Never dump used antifreeze on the ground or pour it into drains.

All cars are slightly different, so if it is time to change your coolant, use our before you begin checklist, and find your car for specific instructions.

How to change your coolant

Here's an example of how it's done

A very brief summary of the task:

  1. Make sure the engine is cold and raise the front of the vehicle on jackstands. You may need to remove the underbody shield
  2. Place a container under the radiator and undo the drain valve
  3. Remove any other drain plugs as instructed by Haynes. Flush the system as many times as necessary
  4. Refill the system with the correct antifreeze, following Haynes’ instructions for bleeding/topping-up procedures

Why you should change your coolant

Periodically, the cooling system should be drained, flushed and refilled to replenish the antifreeze mixture and prevent formation of rust and corrosion, which can impair the performance of the cooling system and cause engine damage.

Over time the antifreeze chemicals in the coolant lose their effectiveness, especially if you top up the coolant with water regularly. In harsh winter weather this can lead to the coolant freezing and expanding, which can damage components.

Tools you will need

Only basic tools are required for this job, although you may need to raise the car to remove the undershield.

  • Pan or bucket to collect water
  • Floor jack (if necessary). Not your car’s emergency jack
  • Axle stands
  • Ratchet and socket set
  • Flat-bladed/Phillips/torx screwdriver
  • Rags
  • Pliers

Parts you may need

  • Coolant
  • New hoses and clamps

How much does new coolant cost?

Coolant £2-£5 per litre
Garage fee savings £100-£150

Every car is different, so before you view the full instructions, find yours…