Several components in your car hold coolant, often called antifreeze, and any of them can get a hole or develop a leak. If your car loses too much coolant, its engine could overheat. Coolant is also extremely poisonous, and its typically sweet smell attracts animals, so it’s best to track down and repair leaks promptly. Some leaks can be fairly easy to find and fix. Others … not so much.
Related: What Is a Radiator?
Coolant can be found in the engine, the water pump at the front of the engine, the radiator, the radiator overflow tank and the heater core behind the dashboard, along with the valves and hoses that connect them. Those components combined are part of the cooling system, which is kept under pressure by the radiator cap. That pressure not only raises the boiling point of the coolant, it also helps keep the circulating coolant from bubbling, which could cause “hot spots” in the engine. Unfortunately, that same pressure also amplifies any leaks.
Tracking Down a Coolant Leak
Most of the aforementioned components are found under the hood, so any coolant leaking from them will end up on the ground under the engine compartment. Exceptions are the heater core, which is located behind the dashboard, and the engine’s cylinder-head gasket, which we’ll get to in a bit.
Coolant is typically green or orange, but it’s sometimes pink or other colors. If you look in your coolant reservoir or remove the radiator cap (make sure it’s cool to the touch first), you can determine what color fluid you’re looking for.
Coolant leaks aren’t always easy to find, as air blowing through the front of the car (either due to the radiator fan or road speed) can spread coolant all over, and that means the puddle you see on the ground may not be directly under the leak.
Nonetheless, putting cardboard under the car when it’s parked might be helpful in tracking down the leak. If you start the car the next morning and let it run awhile without moving it (make sure it’s not in a closed garage), the leak may appear — possibly as a stream or spray — before the radiator fan kicks on and blows the coolant all around. Make sure the air conditioner is off, however, as running it automatically turns on the radiator fan.
Even if you narrow down the vicinity of the leak, seeing where it’s coming from can be tricky, particularly on newer cars that have covers almost completely hiding the engine compartment. If you can see the engine and get an idea as to the leak’s source, you might want to clean off any nearby suspected surfaces with a rag or paper towel and water before running the cold engine to find the leak. It’s a good idea to wear protective glasses and gloves, and make sure to wash your hands afterward.
Likely sources of an underhood leak include (listed roughly in order of cost or difficulty in fixing):
- Radiator cap
- Hose going to the coolant overflow tank, a hose that goes from just below the radiator cap to the overflow tank
- Coolant overflow tank
- Heater hoses and clamps, which usually go through the passenger side of the firewall to the heater core
- Heater control valve and clamps, which is often found inline in one of the heater hoses under the hood
- Radiator hoses (upper and lower) and clamps
- Thermostat housing, typically found at the other end of the upper radiator hose
- Engine freeze plugs, wristwatch-sized plugs in the side of the engine which, should the coolant start to freeze, are supposed to pop out — hopefully preventing the engine block from cracking
- Neck of the radiator onto which the cap latches
- Radiator
- Water pump, along with connecting hoses and clamps
- Engine cylinder-head gaskets
Radiator leaks are sometimes the result of punctures caused by kicked-up stones. Radiators are made up of several separate tubes and tanks joined together, and sometimes those joints end up leaking, often due to old, acidic coolant eroding the joints. That’s why you should have the coolant changed at intervals recommended in your car’s maintenance schedule. Other parts, such as hoses or the water pump, just get old and wear out, while others may crack due to the coolant freezing.
What if I’m Losing Coolant but Don’t See a Leak?
If you’re losing coolant but don’t see drips or puddles on the ground, the coolant might be leaking inside the engine or from the heater core.
Bad cylinder-head gaskets can leak either to the outside, which will leave spots on the ground, or into the engine’s combustion chamber. In the latter case, coolant gets burned with the normal air-fuel mixture, typically creating white exhaust smoke. Replacing a head gasket is a major ordeal.
The same applies to the heater core. Usually located behind the passenger side of the dashboard and very difficult to access, the heater core is like a small radiator. Warm coolant pumped into it heats it up, and air is blown through it to warm the car’s interior. The heater control valve starts or stops the flow of coolant to the heater core based on your cabin temperature settings. If the heater core is leaking, you may see drips from under the passenger side of the dash or find the carpet to be wet. You may also notice the windows fogging up and the sweet smell of coolant.
If your problem seems to be the heater core, you can minimize the leak — and, thus, the chance that low coolant will cause your engine to overheat — by turning your temperature control to “cold.” That will close off the heater control valve and limit how much coolant is pumped to the leaking heater core. While this may act as a bandage, you’ll still need to get it fixed — which is the same advice as for any coolant leak.
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- What Is Coolant and Is It the Same as Antifreeze?
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