Your car's radiator is essential for the ongoing cooling of your engine. If it springs a leak, your engine could overheat and, if left for a long time, the resulting engine damage could cost you a lot of money, or even - in a worst-case scenario - write off your vehicle.
Car engines generate a huge amount of heat. Most of this escapes through the exhaust system, but a good deal lingers around the engine itself. The radiator system dissipates this heat, but if the coolant contained within starts to leak, the engine may overheat.
It's important to carry out regular checks on your radiator to spot any leaks as soon as they occur. A classic tell-tale sign is a patch of coolant fluid appearing on the ground under your car after it has been parked up - if it's petrol on the ground, you might have a fuel leak.
How to tell if it's coolant on the ground beneath my car or oil
Coolant is a sticky fluid, often of green or orange colouration. Oil, by contrast, is either yellowish if it's new, or brown/black if it has been in the system for a while. Models with air-conditioning systems may also leak water from condensation - but this, of course, is easy to distinguish from coolant or oil.
How to check the coolant reservoir for a leak
If you think your vehicle is leaking, make a note of the fluid level in your coolant reservoir - you can do this with a pen or take a photo. Check back after a while driving and see if the coolant level has reduced. If you initially check the coolant level when the engine is cool, be sure it is cool when you re-check (as the fluid can expand when hot). If the fluid level is lower on the second inspection, you do have a leak.
Can rust cause a leak in car radiator?
If you spot rust or discolouration around the radiator, there could be a leak in that area. Rust can appear in many parts of your car, but a concentrated zone of rust around your radiator suggests a leak.
How to fix a car radiator leak
The simplest way to remedy a suspected radiator leak is to take your car to your local garage. If you want to tackle the job yourself, follow the safety advice below.
Allow the engine to cool before inspections begin
When hot, your radiator system is highly pressurised. As such, you must wait several hours for the engine and radiator to cool down before attempting to locate the leak.
Wear safety glasses
Even after the engine has cooled, the system could remain under pressure and expel gas when the radiator cap is opened. As such, it is important to wear safety glasses. As an additional safety measure, you may wish to wear gloves.
Clean the radiator
It will be much easier to identify a leak if your radiator is clean. Use a hose to spray off any grease and grime. Wipe down with paper towels.
Start the engine
Turn over the engine and inspect the radiator for leaking fluid or steam.
Use a coolant system pressure tester
You may decide to use a coolant system pressure tester to find leaks. These are available from car parts stores and garages. Remove your radiator cap and fit the pressure tester to the hole. Use the tester to pump pressure into the coolant system. Locate the sound of leaking air to find the fracture.
Use a leak sealant
You can buy a commercial leak sealant to repair any crack, which must be applied when the engine is cool. This is added directly into the cooling system, topped off with a coolant/water mixture. Fixing the problem with sealant is unlikely to be as effective or long-lasting as a professional radiator repair or epoxy (see below).
Seal visible cracks with epoxy
Epoxy is more effective than leak sealant. You can buy this from any garage or car parts shop. Ensure the area is clean and dry before application and leave overnight to set.
If after reading our tips, you've put yourself off attempting to fix your car radiator leak yourself, you can always enlist your local garage to address the problem. This will be the most costly option, but you’ll save time (compared to fixing it yourself) and you’ll know the repair will last a long time.