Frozen engine, burst radiator: Lack of antifreeze can seriously damage your car.

Many drivers remember winter tyres, an ice scraper and door seals, yet the cooling system is often left out of the checklist. That’s exactly where a hidden risk sits-missing or ageing antifreeze in the coolant. It may sound minor, but in freezing weather it can decide whether your engine survives or suffers damage so severe the car becomes uneconomical to repair.

Antifreeze in the coolant: an unremarkable liquid with expensive consequences

In the expansion tank, antifreeze often looks like nothing more than coloured fluid. In reality, it’s a carefully engineered mix-usually ethylene glycol or propylene glycol-blended with water and a package of additives.

This mixture has three key jobs:

• It lowers the coolant’s freezing point well below 0 °C.
• It raises the boiling point, helping prevent overheating in summer.
• It protects the inside of the cooling system against rust and deposits.

Without antifreeze, water can freeze inside the engine block, expand, and crack components from the radiator and water pump right through to the cylinder head.

The coolant also lubricates moving parts such as the water pump. Meanwhile, corrosion inhibitors form a protective film on metal surfaces and slow internal deterioration. As coolant ages-or if it is repeatedly topped up with plain water-those protective additives are gradually depleted.

What frost can actually destroy in a car

If temperatures fall well below zero and there’s too little (or no) antifreeze in the system, the water content starts to freeze. The issue isn’t just ice-it’s expansion. When water freezes, it increases in volume, generating extreme pressure in parts that were never designed for it.

Engine block and cylinder head: high-risk components

Frozen coolant can create enough force to fail the weakest points first, including:

• hairline cracks or fractures in the engine block
• cracks in the cylinder head
• leaking or displaced core plugs (also known as freeze plugs)

A cracked engine block is usually not cost-effective to repair. Especially on older vehicles, garages may class it as an economic write-off.

Radiator, hoses and water pump: the next likely victims

Ice within the system can also:

• split the radiator
• tear coolant hoses
• jam or destroy the water pump

Split hoses or a damaged radiator are often only discovered on the next drive-when the engine temperature suddenly climbs and steam appears from the engine bay.

Skipping a simple winter check that might cost around £50 can lead to four-figure engine repairs later.

When your engine is asking for help: warning signs to take seriously

Cooling-system and antifreeze problems rarely appear with no clues at all. Common signs to watch for include:

• The temperature gauge rises unusually quickly or heads into the red.
• A coolant warning light illuminates on the dashboard.
• Coloured puddles under the car, often green, yellow, pink or blue.
• A sweet smell in or around the car, especially after a journey.
• Steam or “smoke” from the engine bay.

If any of these occur, avoid driving the car further and arrange professional help. Continuing with low coolant can cause overheating damage-even in winter.

How to check antifreeze in the coolant yourself

A quick look under the bonnet is often enough to rule out the biggest risk. Many people feel unsure about doing this, but it’s usually straightforward.

Step-by-step check

1. Let the engine cool completely-wait at least 30–60 minutes after driving.
2. Open the bonnet and locate the coolant expansion tank (often translucent plastic, typically marked with a thermometer symbol).
3. Check that the level sits between the MIN and MAX marks.
4. Inspect the coolant’s appearance: heavy browning, cloudiness or visible debris suggests trouble.
5. If you’re unsure, ask a garage or service station to measure the antifreeze strength.

Never open the coolant cap on a hot engine-pressurised hot coolant and steam can cause severe scalds.

Extra tip (often overlooked): concentration matters. Many cars are best protected with roughly a 50/50 mix of antifreeze and distilled water (always follow the vehicle manufacturer’s specification). Too much water weakens frost protection; too much concentrate can reduce heat transfer and cooling efficiency.

Which antifreeze belongs in which car?

Modern engines can react badly to the wrong coolant type. The days when “any coloured antifreeze will do” are long gone.

Three practical rules prevent expensive mistakes:

• Follow the manufacturer’s specification: the owner’s manual or service documentation states the required coolant standard.
• Don’t mix types at random: different chemistries can react and form sludge, restricting flow.
• Dilute only with distilled water: tap water can introduce limescale and minerals that clog narrow passages.

Many workshops now use test equipment that displays frost protection in degrees (often down to about –25 °C or –35 °C). For a typical winter in much of Europe, around –25 °C is commonly sufficient; colder upland or mountain areas may justify additional protection.

Change intervals: antifreeze isn’t “fill it and forget it”

Even when the level looks perfect, coolant can lose its protective properties as corrosion inhibitors and anti-deposit additives break down over time.

As a general guide:

• replace coolant every 2–4 years, or
• after about 40,000–60,000 km
• some long-life coolants last longer-check the service schedule for the specific vehicle

If you’ve bought a used car and the maintenance history is unclear, a full coolant change is often a sensible precaution. It typically costs far less than replacing a radiator, water pump or major engine parts later.

Common myths that become costly in winter

A few persistent misconceptions around antifreeze lead directly to preventable damage:

• “I’ll just top it up with water-it’s cheaper.”
  This dilutes the antifreeze and reduces frost protection. After repeated top-ups, the system can end up dangerously close to running on water alone.
• “It’s in a garage, so it’ll be fine.”
  Many garages are unheated. During prolonged cold spells, temperatures inside can still fall below 0 °C.
• “It only does short trips, so it won’t matter.”
  Short-trip driving can hide problems because the engine may not reach stable operating temperature, and warning signs can appear later than expected.

More than frost protection: cooling, corrosion control and engine longevity

Although antifreeze is strongly associated with winter, the coolant protects the engine all year. In summer it helps prevent boiling and overheating; in winter it prevents freezing. At the same time, it reduces corrosion and limits deposits in narrow coolant passages, including those in the heater matrix.

If those passages begin to block, cabin heating can weaken and the engine may cool unevenly. Over time, that can contribute to cylinder-head warping, head-gasket leaks and oil–coolant contamination-classic, expensive engine failures.

Keeping the coolant and antifreeze in good condition can add years to an engine’s working life-for only a few pounds per year.

Safe handling and disposal (often missed, but important)

Antifreeze is hazardous if swallowed and can be particularly dangerous to pets due to its sweet taste. Clean up spills promptly, store containers securely, and never pour old coolant down drains. In the UK, waste coolant should be taken to a council household waste recycling centre that accepts hazardous liquids, or handled by a garage during servicing.

A practical winter routine for drivers

A simple routine keeps the risk under control:

• In autumn, check the coolant level and have the antifreeze strength tested (or test it yourself).
• At every oil service, ask for the coolant condition and protection level to be checked.
• Treat colour changes, cloudiness or rusty particles in the expansion tank as early warning signs.
• Don’t ignore warning lights or a rising temperature gauge-act immediately.

Especially on older vehicles, reliability often comes down to how well “invisible” systems are maintained. Tyres, brakes and bodywork are obvious; the coolant circuit is hidden-until it fails.

If you’re not confident, it’s better to visit a garage or inspection centre once too often than once too late. The test usually takes only a few minutes, costs little, and can prevent a severe cold-weather engine shock.