11 Causes of a Burning Smell in Your Car
Internal combustion engines work on the principle of burning things to go faster. Ironically, you probably won’t notice a burning smell while driving down the road.
If you notice a burning smell in or around your car, it’s important to identify the cause and solve the problem. Some flammable materials can be very dangerous and can even cause a fire.
We’ve done our best to put these different smells into words, but smells can be very subjective and difficult to describe. If you’re still not sure what’s causing the burning smell, ask a trusted local mechanic for advice.
Causes of the Burning Smell
1) Brakes
Brakes slow your vehicle by converting the vehicle’s kinetic energy into heat energy. Of course, excessive heat can make your brakes smell like they’re burning.
When your brakes are burning, they smell like burnt carpet. It’s an organic yet metallic smell that gets stronger the closer your nose is to the wheels. A burning smell coming from your brakes is not something to be taken lightly. Therefore, it is important to find out what is causing your brakes to get very hot.
Brakes work well
Even if your brakes are working perfectly, they can start to cause chaos in the car when you brake hard. Examples of strain on your brakes include driving downhill, repeated sudden stops, and even one emergency stop from a high speed.
If you notice a brake smell after heavy use, make sure to let your brakes cool before driving long distances, especially if you will need to brake hard in the near future.
Not letting your brakes cool can warp your rotors or cause brake fade. Brake fade is the loss of braking ability due to exposure of brake components to heat. In extreme cases, brake fade can even result in a complete loss of braking performance.
If you experience brake fade, you should replace your brake fluid. When brake fluid boils, air gets into the lines and the existing brake fluid can’t withstand the heat as well as it used to.
Worn Brakes
As brake components wear out, they become less heat resistant. Brake fluid is hygroscopic and will absorb moisture over time. This lowers its boiling point. While liquids are virtually incompressible, gases can be easily compressed.
When brake fluid boils, the liquid brake fluid turns into a gas. This gas cannot provide the clamping force that the driver desires because most of the pedal travel is used to compress the gas rather than compressing the caliper. This results in extremely reduced braking effectiveness, causing you to press the brake pedal to the floor with little to no slowing.
Brake pads dissipate heat through the pad material. When brake pads are worn down to the backing plate, they are much less heat resistant than when they were new.
Brake discs also lose their ability to dissipate heat if they are replaced too frequently. For this reason, every vehicle has a minimum brake disc thickness. If the rotor is too thin, it increases the risk of excessive lateral runout, which is commonly referred to as rotor warping.
Stuck Brake Caliper
A stuck caliper means that the caliper cannot release its clamping force on the brake pads of a particular wheel. This keeps the pads partially or fully connected to the rotor, creating a constant braking force on the wheel as you drive down the road.
Under this constant braking force, the brake components cannot dissipate heat, causing the caliper, pads and rotor on that corner to become very hot. If your brake calipers are stuck, you may notice smoke or small fires coming from the corners of your vehicle, caused by the intense heat of the brake pads being forced against the rotor.
Faulty brake hose
When a brake hose is pinched, pressure gets into the caliper but can’t escape. This forces the brake pads against the rotor, causing symptoms similar to a stuck brake caliper.
Braking
During break-in, the brakes are intentionally warmed up to transfer a thin layer of pad material from the new brake pads to the rotors. This coating is an essential component of static friction.
There are actually two types of friction that occur between the brake pads and rotors to slow the vehicle: abrasive friction and adhesive friction.
When most people think of “friction,” they think of abrasive friction. Abrasive friction breaks down the molecular bonds between the pad material and the brake rotor. This causes wear as the two surfaces, the brake disc and the brake pad, rub against each other.
Adhesion is the “stickiness” between the pad material and itself, which requires a thin layer of brake pad material to be around the surface of the disc. When the brake pad rubs against the disc, it adheres to this thin layer as the disc passes over the pad, and breaks the bond as it moves away.
If you’ve just replaced your brakes and are breaking them in for the first time (and you should always break them in with a new set of pads), your brakes will almost certainly emit an odor during the break-in process. This is normal and expected. Brakes get pretty hot when braking properly. Therefore, always allow the rear brake pads to cool before applying the handbrake to prevent them from sticking to the rotor.
2) Clutch (Manual Transmission)
Nobody likes the smell of a burnt clutch. Since it’s hard to access the clutch, the smell of a burnt clutch can also be the smell of burning money.
A burning clutch smells like burnt rubber. It’s a bit like burning brakes, but more organic and less metallic. Think burnt rubber and burnt popcorn. This smell is often felt inside the car, but in some cases, it can also be smelled outside the car. Excessive clutch slippage can also cause smoke to come from the engine bay.
You are most likely to experience a clutch smell if your clutch is slipping excessively. You may be intentionally slipping the clutch when you partially depress the clutch pedal. This can be done, for example, when driving your car up a steep hill. Sometimes the clutch slips even though it should be fully engaged.
This usually happens when the clutch is worn out and needs to be replaced, but it can also happen when the clutch pedal needs to be adjusted. A slipping clutch can often be identified by increasing the engine speed without changing the driving speed.
3) Burned out electrical system
Modern vehicles have many computers and require a maze of electrical cables to connect to fuses, sensors and other computers.
Blown fuse
Fuses protect electrical systems from excessive current. A fuse will blow if the current draw is higher than the fuse is intended for. This prevents current from flowing and protects electrical components.
If the fuse keeps blowing, there’s a problem with the electrical system in its path. Make a wiring diagram and see which components are connected to this fuse.
Then grab a multimeter and test the various parts of the electrical system that share the blown fuse to make sure they’re within factory specifications.
Electrical Short
An electrical short means that the current path completes a circuit in a different way than the circuit was designed for. This can cause excessive current to flow through the system, which can cause a fuse to blow.
When current flows between two wires with poor insulation, an exposed wire can cause a short circuit. If there is no fuse to prevent a short circuit, an electrical short can also cause a cable to heat up to the point where the insulation melts.
Melted Insulation
The wires in a vehicle’s electrical system are encased in a wiring harness to protect them from the hot engine compartment and ambient conditions. If any part of the wiring harness comes into contact with a hot part of the engine (such as the exhaust manifold), the insulation can melt. Molten insulation will smell like burnt plastic and can also cause a short circuit.
Arcing Electricity
Arcing electricity has a distinctive electric smell caused by the formation of ozone gas. This smell can be described as burning chlorine.
If a high voltage component is not properly insulated and is close enough to jump to a nearby conductive surface such as metal, electricity can develop. Spark plugs, ignition coil packs, and spark plug wires are three components designed to handle high voltages.
Be careful with arcing electricity. It is powerful enough to deliver a severe shock and can easily cause an engine fire if it ignites flammable materials such as fuel.
4) Air Conditioning
The HVAC system is connected to the vehicle’s cooling system through the heater core, or if you have air conditioning, it’s connected as well. A burning smell coming from the HVAC system could indicate a problem with one of the other systems.
Moldy Smell on Startup
It’s not necessarily a burning smell, but it’s common for your HVAC system to have a slightly moldy smell when you first turn on the blower motor. Sometimes, your HVAC system needs to clear out a bit of dust and other particles before you can drive odor-free. This is especially true the first time you turn on your car’s heater.
Faulty Heater Core
The heater core is a small radiator that uses hot coolant from the engine to heat the interior of your car.
If your heater core coolant leaks, it can cause foggy windows, overheating of the engine, and a burning rubber smell.
Dirty Cabin Air Filter
Most modern cars are equipped with cabin air filters, but these filters are often forgotten and ignored. A dirty cabin air filter can produce all sorts of odors, none of which are unpleasant. Replacing a dirty cabin air filter is a cheap and easy way to freshen up your car’s interior.
Faulty Blower Motor
A faulty blower motor or blower motor resistor can cause too much voltage or too little resistance, which results in the fan spinning faster than intended and a burning smell. If the casing melts, you might smell like burnt plastic or an electrical smell.
Overheating Air Conditioning Compressor
When the coolant level is too low, your air conditioning compressor has to work harder to pump the remaining coolant through the system. If the system overheats, you may experience a burning smell.
5) Foreign Objects
Maybe your car is perfectly fine, but you picked up a plastic bag floating on the road and it ended up getting stuck in your exhaust pipe.
If you smell something burning and can’t identify it, it’s a good idea to do a quick check of your car to see if anything has dripped or gotten stuck in a hot part of the car. The exhaust system has some of the hottest components in the vehicle, so that’s a good place to start.
6) Engine Oil Leaks
Oil dripping onto the sidewalk is a nuisance that can stain your driveway. Dripping oil down the exhaust pipe is a serious problem that can cause an engine fire. When oil is burning, it’s easy to spot because it will give off a burning oil smell on the dipstick.
Motor oil has a relatively high flash point compared to gasoline, but it can still burn under the right conditions. If you smell burning oil coming from your car, have it inspected to make sure the oil isn’t a fire hazard.
Please note: Oil that leaks from a vehicle cannot lubricate the engine. If you notice oil leaking or burning, you should check your engine oil level more frequently. Running out of oil in your engine can cause fatal damage to your engine.
Recent Oil Change
If you or a technician changed your oil recently, the oil filler cap may be leaking oil into the warm parts of your engine. If the leak is very small, it may eventually burn off on its own without causing any problems.
Frequent Oil Leaks
Oil can leak from a variety of places, but the most common are:
– Valve cover gasket
– ​​Oil pan gasket
– ​​Drain plug
– Oil filter housing
– Camshaft seal
– Front and rear crankshaft seals (main seals)
7) Melted drive belt
A melted drive belt (also called a serpentine drive belt or accessory drive belt) will smell like burning rubber and is often accompanied by a high-pitched squealing noise. High engine part temperatures or a stuck pulley can cause the drive belt to melt.
A stuck PTO pulley creates a lot of friction on the drive belt, which heats up. This belt slippage causes a bad squeal. If you notice a belt squeal, make sure the PTO belt tension is adjusted correctly and that all PTO pulleys rotate smoothly.
8) Loose Hoses
Fuel and vacuum hoses can melt when they come into contact with hot engine parts. You may smell burning rubber or plastic. Engine hoses must be secured with clips at the factory to prevent melting and excessive vibration. On older vehicles, these clips can become lost or broken.
Replacement clips can be purchased from your dealer or parts store. As a simple alternative, cable ties are great for securing hoses.
If you use cable ties near hot components, check the heat resistance of the cable tie to make sure it can withstand the ambient temperature it will be exposed to. Once you have tightened the cable tie, cut off any excess length. Do not place cable ties near exhaust vents or where they may come into contact with other hot components.
9) Clogged Catalytic Converter
A catalytic converter converts toxic gases which produce that rotten egg smell into less harmful emissions. Catalytic converters have an operating temperature in excess of 800 degrees Fahrenheit (427 degrees C). If a catalytic converter becomes clogged, it has the potential to start a fire since the exhaust system is so hot.
A clogged catalytic converter may exhibit other symptoms such as sluggish engine performance. It will often glow when it’s too hot.
10) Misfire or Partial Combustion
Partial or incomplete combustion usually smells like gas and the source of the smell is often the tailpipe. However, you may also smell gas from inside the cabin.
Incomplete combustion could be caused by many factors and is often accompanied by a check engine light on newer vehicles. You are also likely to experience sluggish acceleration.
Poor Engine Calibration
If your engine is tuned improperly, your vehicle is probably running with a suboptimal air fuel ratio. An air fuel ratio that is too rich will smell like gas.
Leaking Fuel
Leaking fuel will likely cause the car to run lean and throw lean check engine lights. This is because fuel is spilling out before it reaches the combustion chamber. Leaking fuel is very dangerous because it could easily ignite and start a fire.
11) Gear Oil Leak
Gear oil is the stuff that lubricates your transmission or differential. It has a distinctly different smell than engine oil, both when it’s fresh and when it’s burning. Burning gear oil is acrid like a burning clutch, but smells a bit more like very burnt bacon. If you’re leaking gear oil and it drips onto the exhaust, it will likely stink up the cabin every time you come to a stop.
Locating the Source of the Burning Smell
There are several steps you can take yourself to locate the burning material.
1) Inspect the Exterior
If you are driving and you smell something burning, pull over as soon as it is safe to do so. Next, get out of the car and do a quick walk around the vehicle. Look for anything obvious like a fire.
2) Inspect the Engine
If you see any smoke coming from under the hood, do not attempt to open the hood. Opening the hood will provide a fire with more oxygen and create a dangerous situation.
Open the hood if you feel it is safe to do so. Look for anything melted, smoking, or smoldering. The smell should be stronger near a melted component.
3) Perform the Sniff Test
While working your way around the vehicle, try to locate where the burning smell is strongest.
To narrow the problem down, start at the engine and smell the air around you. Next, move to the back of the vehicle and take a sniff. Which side is stronger? Keep splitting sections of the car in half until you reach a point where you have found the strongest smell.
Can You Drive With A Burning Smell?
Look around the source of the smell for anything that is obviously wrong. If the burning smell is strong and you’re not sure if it’s safe to drive the vehicle in its current condition, have the vehicle towed to a shop for a diagnosis of the problem.
For milder smells, you may be able to drive the vehicle to a shop safely under its own power. Only do this if you’re comfortable with the risk, the vehicle otherwise drives fine, and there is no visible smoke. If the smell gets worse or you see smoke, stop driving immediately.
