How to Top Up Engine Coolant
Learn how to safely check and top up your engine coolant to prevent overheating. Essential maintenance for UK drivers.
⚠️ SAFETY FIRST - READ THIS
NEVER open the coolant reservoir when the engine is hot!
Hot coolant is under pressure and can spray out, causing serious burns. Always wait until the engine is completely cold (at least 30 minutes after driving).
If your car is overheating, pull over safely, turn off the engine, and call for help. Do NOT open the bonnet immediately.
What You'll Need
- Coolant/antifreeze (correct type for your car - check handbook) - £10-15
- Distilled or deionized water (NOT tap water) - £2-3
- Clean cloth or rag
Step-by-Step Instructions
1. Wait for Engine to Cool
Park on level ground and wait at least 30 minutes after driving before opening the bonnet. The coolant system is under pressure when hot.
⚠️ NEVER rush this step. Touch the bonnet - it should feel cool to the touch.
2. Locate the Coolant Reservoir
Open the bonnet and find the coolant expansion tank. It's usually a semi-transparent plastic bottle with MIN and MAX markings, often with a yellow or orange cap.
Tip: Don't confuse it with the radiator cap (usually metal) - always use the expansion tank.
3. Check the Level
Look at the side of the reservoir. The coolant level should be between the MIN and MAX marks when the engine is cold.
- Below MIN: Needs topping up urgently
- Between MIN and MAX: Level is fine
- Above MAX: Too much - don't add more
4. Open Cap Carefully
Place a cloth over the cap and slowly unscrew it. If you feel any pressure or heat, stop immediately and wait longer for the engine to cool.
⚠️ Open slowly - there may still be some residual pressure.
5. Add Coolant Mixture
Pour in a 50/50 mixture of coolant and distilled water (or use pre-mixed coolant). Add slowly until the level reaches the MAX mark.
- 50% coolant + 50% distilled water
- Or use ready-mixed coolant
- NEVER use tap water (contains minerals)
6. Replace Cap and Check
Screw the cap back on tightly. Start the engine and let it run for a few minutes with the heater on full. Check the level again when cool. If level drops, top up again - some air may have escaped.
Coolant Types & Colors
Different cars need different coolants - never mix types!
| Color/Type | Best For | Change Interval |
|---|---|---|
| Green/Blue (OAT) | Older cars (pre-2000) | Every 2-3 years |
| Orange (HOAT) | 2000s cars | Every 5 years |
| Pink/Purple (OAT) | Modern cars | Every 10 years or 150k miles |
⚠️ Never mix different coolant types - Mixing coolants can cause corrosion and engine damage.
Always check your owner's manual for the correct coolant type and specification for your specific vehicle. The information above is for general guidance only.
When to Check Your Coolant
- Once a month - Regular checks help spot leaks early
- Before long journeys - Especially in hot weather
- If temperature warning lights up - Stop immediately and call for help
- Every 2-10 years - Full coolant replacement (depends on type)
⚠️ When to See a Mechanic
- • Coolant level drops frequently
- • Puddles of coolant under the car
- • Temperature gauge runs hot
- • Sweet smell from engine bay
- • White smoke from exhaust
Track Your Coolant Changes
Record coolant top-ups and flushes in AutoChain. Get reminders when it's time for a coolant change and keep your engine running cool.