EXPERT IN AUTO PARTS
27 November 2025 (updated) Table of Contents
Choosing the right engine coolant is crucial to protecting your engine, ensuring reliable performance in all weather conditions, and avoiding expensive repairs. It regulates your engine’s temperature, prevents overheating, and helps stop corrosion inside the system.
In this guide, we’ll cover everything you need to know about engine coolant: what it is, how it works, which type to choose, and when it should be replaced.
While the terms antifreeze and coolant are often used interchangeably, there is technically a difference. Antifreeze is a concentrated, glycol-based fluid, typically made from ethylene glycol or propylene glycol.On its own, it can’t cool the engine effectively. It must be diluted with water (usually 50/50) to form coolant, the liquid that circulates through your engine’s cooling system.
It mixes with the water in the reservoir to prevent it from freezing up. It also reduces its boiling point and prevents the metal parts of the motor from overheating and corroding. The coolant mixture absorbs heat from the engine and releases it through the car cooling system radiator.
While it’s more convenient to purchase pre-mixed car engine coolant, buying concentrated antifreeze and diluting it yourself can be more economical if done correctly.
Coolant is more than just a temperature-control liquid. It plays several roles in maintaining the engine’s health:
Driving with old or insufficient coolant increases the risk of major damage to internal engine parts, such as blown head gaskets or cracked cylinder heads.
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£10.99
£2.20
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: MN4012-10
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£22.99
£2.30
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: PM0912-10
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£18.99
£1.90
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 86001APC
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£20.49
£20.49
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 99 92 2268
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£28.99
£5.80
for 1 litre
price incl. 20% VAT, excl. delivery costs
Coolants are usually classified by the type of corrosion inhibitor technology they use. The three main types are IAT, OAT, and HOAT coolant fluid (antifreeze).
Types of antifreeze explained
IAT coolants work quickly but degrade fast, which is why they require more frequent replacement.
OAT coolant is efficient and low-maintenance but unsuitable for older engines with copper or brass parts.
Important! Never mix different coolant types. This can cause adverse chemical reactions leading to sludge or blockages in the radiator and water pump.
The safest way to choose the correct coolant is by checking your vehicle’s owner’s manual or using a trusted product compatibility tool on the supplier’s website.
Many people believe the coolant colour alone indicates its chemical makeup, but this is no longer a reliable method. Manufacturers often use different dyes for marketing purposes, so colour can vary even within the same coolant category.
Historically:
However, to avoid confusion and ensure compatibility, you should always go by the coolant’s specification (such as G12++, G13, or Dex-Cool) rather than the colour alone. When in doubt, consult your manual or ask a mechanic.
The replacement interval for coolant depends on its type, your vehicle, and driving conditions. As a general guide:
Other factors to consider:
You can also test your coolant using a hydrometer or coolant test strips. If the liquid is discoloured, rusty, oily, or contains floating particles, it’s time to flush the system.
Don’t wait until your engine overheats to take action. Look for the following symptoms that may indicate cooling system issues:
Ignoring these warning signs can lead to severe damage and expensive repairs.
Here’s a quick guide to selecting the best coolant from AUTODOC experts:
-15%
FEBI BILSTEIN Antifreeze
G11, green, 5l, Ready mixed
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compared to
RRP
£22.99
£19.49
£3.90
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: MN4015-5
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£16.49
£3.30
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 21149
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£8.99
£8.99
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: MN4012-1
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£4.99
£4.99
for 1 litre
price incl. 20% VAT, excl. delivery costs
-17%
FEBI BILSTEIN Antifreeze
G13, violet, 5l, Concentrate
Article number: 38201
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compared to
RRP
£38.99
£31.99
£6.40
for 1 litre
price incl. 20% VAT, excl. delivery costs
Antifreeze contains toxic chemicals (especially ethylene glycol), which can be harmful if ingested by pets or wildlife. Always store coolant safely and clean up any spills immediately. When replacing coolant, dispose of the old fluid responsibly according to local regulations. Many local garages and recycling centres accept used antifreeze for proper disposal.
If you're unsure, consult a mechanic or watch a verified step-by-step video tutorial online. Check out AUTODOC’s handy video guide to inspecting your coolant:
Coolant is one of the most vital yet often overlooked fluids in your car. Using the correct type, checking levels regularly, and replacing it on schedule will keep your cooling system running efficiently and prevent serious engine issues.
Whether you’re maintaining a new model or restoring a classic car, understanding the coolant system gives you the confidence to care for your vehicle properly and avoid expensive surprises later on.
A: Overfilling can cause pressure build-up and lead to leaks or damage. Excess coolant may be expelled through the overflow tube when the engine heats up.
A: Indirectly, yes. An overheating engine caused by poor coolant performance can reduce fuel efficiency and engine performance over time.
A: It’s strongly advised against. Driving with low coolant can cause the engine to overheat quickly, potentially leading to severe thermal damage like a blown head gasket or warped cylinder head.
Top products related to this topic:
Valvoline Antifreeze
G13, yellow, 5l, Ready mixed
FEBI BILSTEIN Antifreeze
G12+, violet, 5l, Concentrate
FEBI BILSTEIN Antifreeze
G13, violet, 1,5l, Concentrate
PEMCO Antifreeze
G11, blue, 10l, Ready mixed, Amine free-Phosphate free
PEMCO Antifreeze
G13, yellow, 10l, Ready mixed, Amine free-Phosphate free
PEMCO Antifreeze
G11, green, 5l, Ready mixed, Amine free-Phosphate free
MANNOL Antifreeze
G12, violet, 1l, Ready mixed, Contains silicate
MANNOL Antifreeze
G12, violet, 20l, Ready mixed, Contains silicate
FEBI BILSTEIN Antifreeze
G12, 5l, Concentrate
MANNOL Antifreeze
G12, red, 5l, Concentrate, Free of nitrite-Phosphate free