Advice Centre

Car Maintenance - How To Guides

Prevent Overheating

Coolant (a mixture of water and antifreeze) is pumped around the engine and cools it down by means of the car radiator. If the level of coolant gets too low, it can cause overheating and serious damage. Coolant should be renewed every two to five years.

How To Guide Overview

  • Tools/materials needed:
  • Antifreeze suitable for your vehicle and weather conditions (check your vehicle handbook or Haynes manual for details); funnel or jug, clean rag

WARNING:

Never undo the coolant filler cap while the engine is hot as there is a danger of scalding. Place a rag over the cap and unscrew it slowly to allow pressure to escape. Wash off any splashes of coolant from the skin (as it's poisonous) and from the car's bodywork (as it can damage paint).

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Step 1 - Check Coolant Level

Most cars have a coolant reservoir with minimum and maximum level marks. With the engine cold, the coolant level should be between the two marks.

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Step 2 - Top up Coolant

If your coolant level is too low (below or near the lower mark), top it up using a 50/50 mixture of water and antifreeze (for normal driving conditions). You can use clean tap water in an emergency, but make up the antifreeze concentration afterwards). DO NOT overfill.

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Step 3 - Refit Cap

Refit the cap tightly afterwards and mop up any spillage.

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Step 4 - Renew Coolant

To renew the coolant, open the radiator drain tap or disconnect the bottom hose.

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Step 5 - Flush the System

If there is a cylinder block drain plug, unscrew it. Flush the system with clean water, or maybe a flushing compound.

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Step 6 - Refill the System

Close the drains and refit any hoses, then refill the system with the correct water/antifreeze mixture.

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Step 6

Some cars have bleed screws that must be opened when refilling to avoid airlocks. Check your vehicle handbook or Haynes manual for details.

Haynes Hints
Haynes Hints

A leaking coolant hose can sometimes be patched up with a hose bandage. This will get you out of trouble until a new hose can be fitted. A leaking radiator will have to be replaced eventually, but adding a leak-sealing compound to the coolant reservoir will sometimes fix it for a while. A clogged-up radiator can cause overheating. Try using a cooling system flushing compound to clear it. If the engine starts to overheat when you’re driving and you can’t stop immediately, put the heater on (maximum heat, highest blower speed) to disperse some heat.