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Prevent Overheating

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Stop your car from getting hot under the collar with our guide on how to prevent overheating.

Prevent Overheating

Coolant (a mixture of water and antifreeze) is pumped around the engine, cooling it down by means of the car radiator. If the level of coolant gets too low, it can cause overheating and serious damage. It's best to renew your coolant every 2 to 5 years.


You'll need:

Antifreeze suitable for your vehicle and weather conditions (check your vehicle handbook or Haynes manual for details)

Funnel or jug, clean rag


Never undo the coolant filler cap while the engine is hot as you could scald yourself. 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).

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.

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!

Step 3 - Refit Cap

Refit the cap tightly afterwards and mop up any spills.

Step 4 - Renew Coolant

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

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.

Step 6 - Refill the System

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

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

Top Tips

  • Leaking coolant hose? Sometimes they can be patched up with a hose bandage until a new hose can be fitted. You  could also add a leak-sealing compound to the coolant reservoir as a short-term fix
  •  A clogged radiator can cause overheating. Try using a cooling system flushing compound to clear it
  • If the engine starts to overheat whilst you're driving but you can't stop immediately, put the heater on maximum heat and highest blower speed to disperse some heat.
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