Learn the different noises your engine can make, what they might mean, and what you should do.
Let’s face it, internal combustion engines (ICE) make noise when they run. Some engine sounds create outright joy -- like the aural splendor of a V-10 engine at full song, or the chunky low frequency thrum generated by a tall-cam V-8 at idle.
Other ICE sounds, however, are not so joyful.
Everyone knows the fear of things that go bump in the night. The same can be said of your engine -- only in this case, various scary sounds can include banging, clicking, tapping, knocking and other uncomfortable kinds of ear candy.
While some are cause for genuine alarm, most engine noises are simply your vehicle’s way of telling you that something isn’t working properly. So, let’s run through common unpleasant mechanical sounds, what they could mean, and how you might be able to resolve the situation.
Sizzling/Hissing
This sound is most identified right after you shut the engine down. Typically, it involves some kind of fluid or pressure leak. This can include engine coolant, anti-freeze, or in the case of a real threat, oil.
More times than not, the sound itself is usually due to boil-off on hot components. But other times, this kind of noise can be generated by some type of depressurizing event like a malfunction in the engine’s vacuum system, or possible out-gassing from plumbing related to the A/C unit.
Hand Checking Engine Hoses
What Do I Do?
To help determine how serious the issue is, pay attention to any other symptoms the vehicle may be exhibiting -- like a large cloud of steam, a dashboard warning light, or a hissing/sizzling noise that lingers even a few minutes after the vehicle is shut off. These are all signs of an overheating engine, in which case the safest thing to do is pull over, shut off the vehicle and call in the pros.
If you want to peek under the hood and investigate a potentially low coolant level or possible faults in the radiator/radiator hoses, it’s critical that you wait until the engine cools down. Otherwise, you run the risk of seriously burning or injuring yourself.
Sometimes, hissing sounds are caused by a leaking or disconnected vacuum hose. This will usually be accompanied by fast idling, engine hesitation or even stalling. A service center will be able to track down the leak and complete a repair.
Popping
Popping -- sometimes known as uncontrolled detonation -- usually indicates some kind of combustion-related problem. The sound can result from irregularities in the engine’s fuel, the fuel system at-large, fouled spark plugs, ignition-related components, and/or damaged plug wires.
Essentially, all of those components tell the driver that the engine’s combustion cycle isn’t happy and wants some help.
What Do I Do?
A dirty or clogged air filter could be the culprit, as well as worn or corroded spark plugs. Both are simple and (relatively) inexpensive to replace.
A clogged fuel filter could also be to blame for any popping sounds, especially if the vehicle is also experiencing rough idling or hesitation. This, too, is a relatively simple and inexpensive fix – and one you won’t want to put off, as it can lead to fuel pump failure.
If you suspect more serious internal ignition issues are at play, it’s a good idea to bring in a qualified mechanic’s help. Working with a high-voltage system increases the chance of electrical shock.
Clogged Engine Air Filter
Knocking
A metallic knocking sound also relates to uncontrolled detonation, although in this case it is most associated with some irregularity in the engine’s timing.
The cause here can relate to multiple cylinders firing out of order, or in other cases firing simultaneously. Other possibilities can involve fuel/air mixture problems, bad gasoline, or failure of the engine’s electronic knock sensor.
What Do I Do?
Combustion cycle sounds are siblings to popping, and so can also indicate a bad fuel filter or incorrect/damaged spark plugs.
However, knocking could also just be the result of poor-quality fuel. Sometimes, simply switching to a higher-octane rating or even just switching gasoline brands can alleviate the problem. Adding detergents to the fuel can help as well, like an octane booster or a fuel injection cleaner to remove harmful carbon buildup.
If none of these remedies help, you’re probably looking at a more serious issue that requires professional diagnosis.
Tapping
A persistent tapping or clicking sound is usually involved with a low oil level and/or at-large oil pressure. Engines are properly lubricated using specific levels of oil, so if an engine’s oil level is low, components begin to experience increased friction, higher than normal temperatures, the potential of component warping and ultimately, the beginnings of component failure.
Similarly, clicking and tapping can be exhibited when a valve spring has failed, or general valve warping is involved.
What Do I Do?
Usually, a tapping engine sound can be resolved by changing or topping off your oil. Sometimes, the oil pump will need replacement, which is both an affordable and pretty straightforward repair.
If, however, you suspect valve train issues, you could be looking at a more costly and labor-intensive job, so it’s best to have a mechanic check things out.
Mechanic Removing Engine Oil Dipstick
Banging
Nearly everyone has experienced loud banging at the rear of a vehicle. This sound is most likely caused by a backfire somewhere in the rear portion of the exhaust system.
In this event, the cause of banging is usually driven by unburned fuel vapors that have escaped the combustion chamber, resulting from an unbalanced fuel and air mixture -- also sometimes referred to as a “rich condition.”
As a practical matter, fuel vapor is highly explosive, so when heat from the combustion cycle is expelled within the exhaust system, any unburned vapors explode with an ear-splitting bang.
What Do I Do?
Clogged air filters, fuel filters, or fuel injectors could be to blame, as well as a bad fuel pump or damaged spark plugs/wires. Backfiring could also be the result of issues within the EGR system (exhaust gas recirculation), like stuck valves or vacuum leaks. It could even be a sign that the catalytic converter is malfunctioning.
Suffice it to say, there are many potential causes for a backfiring vehicle. So, consider that first one to be your warning shot, and get the vehicle in for a thorough inspection.
Grinding
If you hear a low frequency grinding sound when an engine is turning over there’s usually only one reason for the event -- main bearing failure.
Engine main bearings allow an engine’s camshaft to rotate. Consequently, if bearing-related grinding emerges, the sound usually announces the potential of camshaft failure.
If that happens, the cam will not spin freely, leading to malfunctions of other major components including rods and bushings, thereby ultimately leading to a collapse of the entire engine complex.
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What Do I Do?
If you suspect main bearing or camshaft failure, it’s time to call in professional help.
If you hear grinding when bringing your vehicle to a stop, then it’s time to change those brake pads. Learn how to tackle this DIY-friendly task HERE.
Squealing
Belt systems are not particularly complex, but they are critical to an engine’s operation. Any time you hear a high-pitched persistent or intermittent squeal from an engine, the noise is nearly always related to belts or related mechanical components. These include: pulleys, the engine’s belt tensioner, or other primary mechanical system like the water pump.
If belts are frayed or loose, they will rub against other components driven by engine pulleys and/or its belt tensioning system.
What Do I Do?
If the bad belt in question is a serpentine belt, you’re in luck. These are both inexpensive and simple to replace. Timing belts will require a greater investment (and require special tools), but still fall within the realm of “affordable.”
However, if a timing belt snaps while you are driving, it can cause some serious engine damage. So, don’t ignore the warning signs – which include squealing (and sometimes ticking) sounds, difficulty starting the engine, and possible misfiring.
All engine noises mean something, so don’t wait to take action, unless you’d prefer a sound of silence signifying complete engine failure.