Why is My Car Making a Hissing Noise?
If your car is making a hissing noise, an overheating engine, exhaust leak, or leaking valves could be why. Learn more about what could cause a hissing noise.
Written by Andrew Mata
Reviewed by Carrie Adkins
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If your car is making a hissing sound, it could indicate you have an exhaust leak, a cooling system issue, or a damaged ac valve. Depending on where the noise is coming from and when it happens, it could also indicate other problems.
If your car has recently added a hiss to its vocabulary, the
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Engine hissing
If your engine is hissing, **pullover at the next safe opportunity**.
Continuing to drive with a hissing engine could damage your vehicle or cause harm to you and your passengers. Two reasons your engine might hiss are:
Exhaust leak
Hissing from under the hood could indicate an exhaust leak. This may be as simple as a leaky gasket, or a break in your exhaust manifold or pipe.
Your exhaust system is designed to guide the harmful gasses away from you and your car, so if you think your exhaust might be leaking, it’s important to get this fixed ASAP as you could potentially harm yourself and your passengers. If you’re already on the road, it’s strongly recommended to pull over and
call for roadside assistance
. Engine overheating
If you hear hissing from the front of the car and see your temperature light turn on, pull over and shut off the engine.
If you can still hear the hissing or sizzling noise a few minutes after your car’s been shut off, then it’s likely that your
engine is overheating
.If this is the case, you might see steam rising from under the hood. Do not to touch the hood—if your engine is overheating, the hood will be extremely hot. Instead, call a tow truck or your roadside assistance number.
AC hissing
If your car only hisses when you turn your AC on, then it is likely the culprit. The specific issue could be...
Leaking valves
Your AC will make a hissing noise if there’s a leak within the compressor. These valves help pressurize the gas that cools the air in your AC system. Along with a hissing noise, you may also hear a squealing or shrieking noise.
These noises mean that the pressure is too high in the AC’s compressor—you’ll want to have this looked at by a professional to avoid further damage to your AC.
In this scenario, it should be safe to operate your car as long as you can comfortably drive to an auto repair shop without a fully operational AC.
MORE: How to do summer car maintenance
Hissing when accelerating
If you hear the hissing noise increase as you accelerate the car, the source might be your cooling system. You could also have a problem with a vacuum leak, which means a vacuum line is damaged.
Cooling system damage
While the hoses in your cooling system are designed to withstand high pressure, engine vibration, and high temperatures, hoses experience wear and tear eventually.
Your coolant system is designed to help your engine rise to the optimal temperature quickly, keep your engine an efficient temperature, and remove excess heat from the engine.
Since the cooling system is vital to how well your engine performs, these kinds of fluid leaks should be addressed immediately. If you think you have a cooling system issue, have your car towed to a repair shop to prevent damage to your engine.
Vacuum leak
A vacuum leak could be another reason you hear a hiss when accelerating, particularly if your car seems like it’s idling faster than normal and the Check Engine light comes on.
A vacuum leak means that your car is taking in a lean air mixture, which will eventually cause your car to lose power.
If you think you have a vacuum leak, immediately bring your car into the shop. Have your car towed instead of driving to prevent a possible breakdown.
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FAQs
What does an air leak sound like in a car?
An air or vacuum leak may result in a variety of noises. Hissing is common, but you may also hear a sucking or squealing sound. If you hear anything like this coming from your engine, be sure to have your car looked at by a professional as soon as you can.
What to do if your engine is hissing
If you hear a hissing noise from your engine, you’ll first want to pull over safely and shut off the engine for at least 15 minutes. This is in case your engine is overheating—you want to avoid immediate damage to your engine, and be able to inspect your car safely by allowing the engine to cool.
The next thing you’ll want to do if you can’t see an immediate cause of the hissing noise after inspection is to make an appointment with an auto repair service and use roadside assistance if needed.
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