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Car leaking coolant? Find, diagnose, fix and repair a coolant leak?


Coolant is a key part of your car’s engine. A mixture of antifreeze and water, it keeps the cooling system flowing effectively, raising the boiling point of the water while simultaneously reducing its freezing point.

Without coolant, your car can become damaged and break down from everyday usage or the extremes of hot and cold weather that are becoming ever more frequent. That means a coolant leak can be an especially expensive and frustrating thing for drivers to experience. And what’s more, the smell and taste of coolant can be attractive to animals yet the mono- ethylene glycol in it is toxic, so a leak can put your dog or cat at risk too.

Thankfully though, these problems can be avoided if a leak is fixed quickly. In this guide, we explore how you can diagnose whether your car has a coolant leak, provide coolant leak repair tips, and help you fix a coolant leak in the best possible way.

Please note engine car coolants are hazardous please wear safety gloves and safety glasses when looking for leaks and be careful with inhalation of the fumes.

How to identify whether your car is leaking coolant

Ultimate coolant and antifreeze guide

To work out whether your car has a coolant leak, you need to properly diagnose the problem. Once you’re safely parked, check the following steps to find out whether your car is leaking coolant.

  1. Sweet smell - Antifreeze and coolant are sweet-smelling. That means if you smell it before or after driving, there may be a coolant leak. To make sure you’re smelling the right thing, grab a bottle of coolant and clue yourself up on the odd aroma so you can quickly identify its presence in the future.
  2. Coloured puddles - Coolant can come in blue-green, pink, orange, or lime-green, so if you see a puddle of this under your car after you’ve left it stationary for a little time, then your car may be leaking coolant. Again, make sure you know exactly which type of coolant your car uses before you diagnose the issue, and to make sure it’s your coolant, not a neighbour’s, drive your car so it warms up completely, and then park it on a clean, dry section of your driveway before you look for puddles later on.
  3. Heat problems - If you begin seeing your vehicle’s dashboard temperature gauge rising, this is due to the coolant becoming hotter. Less coolant means a smaller volume of coolant to dissipate heat, so this may be a symptom of a coolant leak too.
  4. Dashboard lights - Your dashboard lights can also indicate a coolant leak. Look out for the coolant warning light and ‘check engine’ light, as these are often the most likely to show if you have coolant issues.

How to find the source of the coolant leak?  

The choice of antifreeze and its ready-to-use, water-mixed form, engine coolant, differs between vehicles. Wondering which to use? This guide will help you find the correct fluid for your car. 


If you’ve discovered any of the above indications, it’s time to work out where the coolant leak is coming from.

Here, you need to properly prepare your car, so drive until it’s warmed up, then park it on a clean, dry, and flat driveway. It’s crucial that you make sure the system has cooled down before you open the bonnet, so wait for an hour or two to give the fluid time to chill, then check off the following:

  1. Find the pool - As we said before, a pool of coolant can mean a leak, but its location can help diagnose exactly which part of the system is leaking.

    If the puddle is towards the front of the car, then the problem may be in the engine bay or radiator. Open the bonnet and begin using your eyes - and nose - to find the source of the leak. As well as leaking coolant, residues the same colour of your car’s specific type of coolant can also be a giveaway.

  2. Smell the source – Beware, coolants are hazardous by inhalation, so be careful when sniffing out the source of the coolant leak in the engine bay, if you smell coolant in the cabin, then it may be a problem with the car’s heater core, which also contains some coolant. This can be a tough problem to fix on your own, given its location deep behind the dashboard, so consider a mechanic if you encounter this problem.
  3. Check the tank - If you can’t find out where your car is leaking coolant from, then double check the coolant tank, opening the cap with a cloth while the car is cool. Top it up to the maximum level, then take the car for a drive. Let the car and tank cool again, then check the reservoir. If the level hasn’t dropped, then a coolant leak is unlikely. If it’s very low or empty, then it’s clear your car is leaking coolant and you should take your car to a technician.

How to fix a coolant leak

If you have found the source of the coolant leak, then you may be able to fix it on your own. Leaky hose clamps can often be tightened by hand or wrench, and if a small amount of coolant is dripping from the hose itself, it may be possible to replace it, if you are able to find the part and are happy following a manual or online tutorial.

That said, many coolant leaks can be in difficult-to-reach areas of the engine, such as deep within the engine bay, behind the dashboard, and the radiator itself. That means if you don’t feel confident performing a coolant leak fix on your vehicle, it’s always a good idea to get professional assistance from your mechanic.

The one thing you shouldn’t do however, is continuing to drive your car. If you continue topping up a car leaking coolant, you’ll not only waste your money on fluid, but pollute your drive and the roads, putting animals at risk in the process. And if you let your coolant leak dry, your engine may overheat from hot weather or usage, or seize up due to freezing cold temperatures. Each of these can end up harming your components, resulting in costly garage bills.

How much engine coolant do i need? 

Your car’s coolant system will typically hold around 5 litres of coolant, though this can differ depending on the make and model. You can find out the exact amount from the handbook or your car dealer.

Engine coolants come in a range of bottle sizes so you should be able to get hold of a pack for a full coolant change or quick top-up - whichever suits the maintenance job to hand.

Can you put water in coolant? 

Yes, you can put water in coolant, with some caveats. First, you should only do so in an emergency, such as if you run low on coolant and your car is overheating while on the road. That’s because automotive cooling systems are designed to run on a mixture of 50% antifreeze, 50% water - coolant. If the mixture is off, the performance of the system will be adversely affected.

If you do choose to put water in the cooling system, you should let your car’s engine cool down and make sure to use a cloth to open the reservoir - which may potentially be full of superheated steam. Be sure to pour in the water very carefully too.

You should also only drive your car to your home, and then take it to a garage as soon as possible to have your cooling system looked over for damage and leaks, the water flushed out, and fresh coolant poured back in its place.

It’s also important you use the cleanest water available as well. Distilled is best, however bottled or tap water can be used in absolute emergencies. The more impure the water source, and the longer you keep driving, the more likely that your cooling system will be hampered by mineral deposits.

Can a coolant leak cause a 'check engine' light?

Yes, a coolant leak can cause a ‘check engine’ light (also known as the malfunction illumination light (MIL) to show on your dashboard.

That’s because the cooling system is crucial to the health and performance of your engine. If your coolant level is low, then your engine will either heat up above, or cool down below, its operating temperature, affecting its function. This can cause the ‘check engine’ light to show.

That’s not all though. If the temperature rises too high, the Engine Coolant Temperature (ECT) sensor itself can be damaged. This means that simply adding more coolant won’t solve the MIL problem, as the engine will understand that there is an error with the ECT sensor. As a result, the ECT may also need to be replaced.

This goes to show just how important it is to keep your cooling system topped up with coolant while on the road.

Choose TotalEnergies' coolant and antifreeze
TotalEnergies COOLELF 

TotalEnergies has a wide range of antifreeze and coolant products available to motorists. GLACELF antifreeze and COOLELF coolant are designed to not just cool engines and stop them from seizing up, but to protect parts from corrosion, improve part lifespans, keep cooling systems clean, and much more. Learn more below or contact our team if you have any questions.