Coolant Smell From AC: 7 Common Causes

When it is hot outside, you want to enjoy the AC in your car. However, when you turned it on, you could smell that sharp, sickly-sweet smell of coolant, otherwise known as antifreeze. Below are some of the common causes of coolant smell coming from your car’s AC.

Why does my car’s AC smell like coolant?

The most common causes of the smell of coolant coming out of your AC are:

  • Your coolant is leaking
  • You have a cracked coolant reservoir
  • A valve leak
  • Loose connectors
  • A heater core leak
  • A radiator leak
  • A head gasket leak

Read on for helpful tips for identifying which of the above issues is causing your AC to smell like coolant and how to fix it.

1. Coolant is Leaking

There are a few different reasons that your car’s coolant could be leaking. There are also a few different ways that it could be leaking. 

The most notable is also the most visible. If the coolant is leaking from a pipe, you’ll notice a pool underneath the vehicle of the coolant and will be able to see it drip from a leak or from somewhere deeper within the car.

This will either be from a leak in the radiator or a broken or punctured pipe.

If you can’t see any of the coolant leaking or pooling underneath the vehicle, the odds are that there is an internal puncture that you just can’t see and the coolant is going somewhere else. 

The way to figure out if this is happening is to look at the coolant in the radiator will dry out fast and you’ll know it’s from a puncture and not some other reason.

2. Cracked Coolant Reservoir

If your car’s coolant reservoir is cracked, it will leak coolant. Depending on where the reservoir is cracked, you may or not smell coolant coming from your car’s air vents if this is an issue. 

If your car is overheating and you have smelled coolant coming from the vents in the past when you turned on your car’s air conditioner, the coolant reservoir is likely cracked.

To determine if your coolant reservoir is cracked, take a peek under the hood and look at the reservoir. If you can’t find it, take your car to a mechanic and tell them about what you suspect. They will find a crack if there is one to be found in the coolant reservoir.

Coolant Smell From AC 1 Coolant Smell From AC: 7 Common Causes

3. Valve Leak

Your car cools itself through a complicated system, and part of the system has valves that bring coolant to various parts of your car.

If one of the valves has a hole, coolant will start to leak. If the valve leaks onto another part of your car, when the engine warms up, the coolant will burn. This may cause you to smell coolant when you turn on your car’s AC.

Most of the time, valve leaks are relatively easy to find. 

However, from personal experience, I know that these leaks can also be extremely difficult to find and fix. Once you find one leak, you will likely find another at a later date.

If you are unable to find a valve leak, take your car to a mechanic. They will do tests to see if they can find the leak and fix it.

4. Loose Connectors

Oftentimes, connectors are used to connect the valves to the rest of the car. If these connectors are not tightened enough, they will not hold the coolant in your car and you will see a leak coming from where the connectors and valves meet. 

Luckily, it is easy to fix this issue. Simply tighten the loose connectors, and you will be good to go.

5. Heater Core Leak

One of the most common causes of a coolant smell coming from your car’s AC vents is a heater core leak. The heater core and your car’s cooling system work together, and many parts are connected to each other. 

If there is a leak in the heater core, you will smell coolant when you turn on your car’s AC.

One sign that your car’s heater core has a leak is coolant on your driveway where your car was parked. 

You may also see fluid, most likely coolant, where your feet go inside of your car. This is a sign that the leak is severe and needs to be fixed as soon as possible. 

Steam will also come from the engine or the AC vents. If you notice fog appearing on your windshield, even though it’s not cold, it is likely caused by steam coming from the vents. 

Unfortunately, it is not cheap to fix a heater core leak, as it may need to be replaced. To replace a heater core or fix a leak inside will cost $250-$900. 

6. Radiator Leak

If your radiator has a leak, you will smell coolant when you turn on your car’s AC. Leaks in the radiator are surprisingly hard to find unless they are severe or you can visibly tell that your radiator has been damaged severely

If you open the hood of your car and see coolant bubbling in the reservoir, there is likely a leak in the radiator. If you are unable to find it, take your car to a mechanic.

7. Head Gasket Leak

If your car’s head gasket has a leak, you will smell coolant coming from your car’s vents. However, that is not the only sign that you will see

You will also see blue or white smoke coming out of the exhaust, white in the oil in your car, and your car’s engine will overheat with seemingly no cause. Luckily, head gaskets are relatively easy to replace. 

Once the head gaskets are replaced, they will keep the oil and coolant separate in your car, so you won’t smell coolant when you turn on your car’s AC.

Keep in mind that you may notice a weird smell coming from your vents when you turn on the AC for the first time in a while. 

You will likely notice this during springtime rather than summer, as depending on the climate of the area you live in, it has been too cold to turn on your car’s AC for a few months.

If you notice an odd smell that is not coolant coming from your car’s AC vents, take your car to the mechanic. Your car may have mold in the filters, which can harm your health over time.

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