If you smell something burning coming from the engine bay it is usually caused by oil leaking onto hot parts of the exhaust, a drive belt that is slipping, brakes that are dragging, an overheated clutch or wiring insulation melting due to an electrical problem. Figure out what the smell is, pull over if it gets stronger and get it checked out as soon as possible.
One of the best diagnostic tools in your car is your nose. Different faults smell very different when they burn and being able to differentiate can save you a much bigger repair bill, or in the worst case an engine bay fire. Here’s what each smell means and what to do about it.
Burning Oil Smell From the Engine Bay
This is the most likely offender. It’s thick, acrid and a little greasy, and usually worsens after twenty minutes or more of driving the car. Almost always this is oil leaking from a gasket or seal and dripping onto the exhaust manifold which is running at several hundred degrees.
The usual suspects are the rocker cover gasket, the sump plug, a weeping oil filter housing or on older European engines, the rear main seal. You can have a strong smell without a puddle under the car because a small leak will burn off before it reaches the ground. Check your dipstick. If the level is down in-between services, the oil is going somewhere.
A rocker cover gasket is an inexpensive repair. However, left to its own devices the oil bakes on to the exhaust, contaminates engine mounts and wiring looms and makes the eventual repair messier and more dear.
Burning Rubber Smell While Driving
A hot rubber smell is almost always a belt or a hose. The serpentine belt runs your alternator, power steering pump and air conditioning compressor. If it starts to slip on a pulley, it quickly gets hot from friction and you get that unmistakable smell and often a squeal on cold starts or under load.
Another option is a rubber hose that has shifted and is rubbing against a hot part. Radiator hoses and vacuum lines age and get soft, and a hose that contacts the exhaust manifold will burn through in weeks. With the engine cold, open the bonnet and see if there are any hoses in the wrong place or any shiny or frayed patches on the belt.
Sweet Burning Smell and Coolant Leaks
Once you know what to look for, it’s easy to tell the difference between oil and coolant. Coolant has a sweet, almost syrupy smell when it’s burning. You can tell if there is a sweet smell coming from the engine compartment, that is coolant escaping and hitting something hot, most often a weeping radiator seam, a loose hose clamp or the heater core connections at the firewall.
Don’t sit on the coolant loss. A slow leak will bring the system level down until the engine begins to run hot. On modern alloy engines one overheating event can warp the head. If you smell sweetness or see the coolant reservoir dropping, get the cooling system pressure tested so the leak point is found before it becomes an overheating problem.
Burning Plastic or Electrical Smell in the Car
Electrical burning smell is sharp and chemical, like melting plastic, and it warrants the most urgent response of anything on this list. This means that the wiring insulation, a relay, a connection in the fuse box or an electric motor is getting hot. Common causes are a seized cooling fan motor, a chaffed wiring loom shorting against the body and aftermarket accessories that are wired in without a proper fuse.
If you smell this, turn off accessories one by one. If it goes away when the heater fan shuts off, then you have a suspect. If you smell something strong or see smoke, pull over and disconnect the battery if it is safe to do so. “Electrical faults are the biggest cause of vehicle fires and they rarely give you a second warning.
Burning Smell After Hard Braking or Towing
Hot, metallic, slightly sulphurous smell, usually after a long descent or heavy towing run. Hard-worked pads become glazed and give off that smell, which usually goes away once they cool down. That version is not a flaw, it is just physics.
While driving normally around suburbia, a brake smell, especially from one wheel, is not normal. That indicates a seized calliper piston or slide pin holding the pad against the disc all the time. You may find the car lacking in power, one wheel running hotter than the others after a drive or notice the fuel consumption creeping up. If so, check the calliper for sticking before the constant heat wrecks the pad, disc and wheel bearing all at once.
A clutch that has been slipped hard, on a steep hill start, or while towing, produces a very similar hot smell in manual cars. Occasional whiffs after heavy use is normal. If you smell clutch while you drive relaxed, the friction plate is going out.
When a Burning Smell Means Stop Driving
If you experience any of the following, pull over immediately:
- Any smell of electrical or melting plastic, particularly with flickering electrics or visible smoke.
- The oil smells strong and the oil level is low, or there is a warning of oil pressure.
- A sweet coolant smell, the temperature gauge inching beyond halfway.
- A brake smell from one wheel during normal driving conditions, especially if the car pulls to that side.
If the smell is faint and does not get worse and there are no warning lights you can normally drive gently to a workshop. Any of the above is enough reason to pull over and have yourself towed. A tow truck is always less expensive than a fire or a cooked engine.
Burning Smell Diagnosis at A to Z Automotive Services
The trouble with burning smells is that the evidence is burnt off before you can get the bonnet up. In our workshop in Cardiff these faults are methodically traced in the following manner: Firstly a cold inspection for staining and residue, secondly a pressure test if coolant is suspected and finally a road test to replicate the conditions which trigger the smell.
If you are in Newcastle or the surrounding Hunter suburbs and your car has developed a smell you cannot place, book an inspection with our team and we will find the source before it finds you. Call 0432 553 905 to arrange a time.
FAQs About Burning Smells From the Engine Bay
Is it safe to keep driving with a burning smell from the engine bay?
If the smell is faint and the temperature gauge is normal, generally short trips at low speeds are acceptable. If the smell gets worse, there’s smoke or the gauge goes up, pull over and shut off. Treat strong smell as urgent. Oil and coolant on hot exhaust parts can catch fire.
Why does my brand new car have a burning smell?
The first few hundred kilometres of a new car often have a slightly burning smell as the protective coatings on the exhaust and engine components are cured by heat. Should go away in a week or two of normal driving. If it continues, or smells like oil rather than hot paint, have it checked.
How much does it cost to find the source of a burning smell?
A workshop inspection to find the cause of a burning smell will usually cost between $100 and $200 AUD depending on how easy it is to get to the source. Then the cost of repair depends on the cause. If the belt needs replacing, it will run a few hundred bucks. A rear main seal leak will run considerably more.
Can a burning smell come through the air conditioning vents?
Yes. The cabin air intake is located near the base of the windscreen and when the fan is on it sucks in smells from the engine bay. If you just smell burning coming out of the vents that could also indicate an overheating blower motor or debris on the cabin filter but that’s a different problem.
