What’s That Smell

NARPRO “Nose” Automotive Diagnostics

Common sense? Steer clear of taste, but your other 4 (touch, sight, hearing, and smell) can help you manage your vehicle. How does your car smell? Not the long gone new car smell, the myriad of smells emanating from your vehicle. Some are perfectly normal, even if they are annoying. Some odors are evidence of something wrong. You–or your mechanic–can tell a lot about the source of an odor by knowing the smell. Some odors are stronger inside the vehicle, some are only present when the car is running, others when it’s hot, others when it’s stationary. When, where and what smells? Here are odoriferous generalizations:

(1) MAPLE SYRUP

WHEN: After the engine has warmed or after it’s shut off for a few minutes.

THE CULPRIT: COOLANT containing sweet-smelling (but toxic) ethylene glycol is leaking from somewhere. It could be coming from a radiator or heater hose, a failed intake manifold gasket or cylinder head. It might be coming from a leaky radiator cap or the radiator itself, especially if you smell it outside the car. A strong odor inside the passenger compartment probably means a bad heater core.

(2) GYM SOCKS

WHEN: It recently rained or you turn on the air conditioning.

THE CULPRIT: It’s good, old-fashioned MILDEW. It’s activated by rain or moisture condensing inside your a/c evaporator. And no, fabric sheets in the vents will net get’r gone. You could turn off the a/c a mile from home and run the fan on high to dry the system out or your mechanic can eliminate the problem.

(3) GAS STATION

WHEN: Parked, especially inside a garage or when the weather is really warm.

THE CULPRIT: This is raw GASOLINE. On older cars–pre-1980 or so–some odor after a hot shutoff is normal from fuel afterboil in the carburetor float bowl. Modern cars have an evaporative-emissions system that’s tighter than our managing editor’s deadline schedule, so any fuel smell means something is wrong. There may be a leak from a fuel-injection line or a fuel-tank vent hose.

(4) HELL

WHEN: All the time, especially when the vehicle was parked after a long drive.

THE CULPRIT: Yes, it really is brimstone also known as sulfur. You may have GEAR LUBE leaking from a manual transmission, transfer case or differential housing. Sulfur compounds in this oil serve as extreme-pressure lubricants for the gears, and can get pretty funky after a few years in service. Look for smelly dribbles of oily stuff under the car.

(5) ROTTEN EGG

WHEN: Any time your engine is running.

THE CULPRIT: Hydrogen sulfide in the exhaust, which is produced by trace amounts of sulfur in gasoline. It’s supposed to be converted to sulfur dioxide in your CATALYTIC CONVERTER. This may be indicative of a fuel-injection problem, and can be cured by a sharp mechanic. But often it means a failed catalytic converter. The bad news: A new converter is expensive. The good news, they are usually warranted to 100,000miles.

(6) SMOKE

WHEN: Any time.

THE CULPRIT: The FIRE? If your vehicle is smoking anywhere at any time it’s time to get some service – immediately. It doesn’t matter if you smell the smoke, or see it – you need to deal with the problem ASAP (BTW “deal with” is not capture smoke in ziplock – no mechanic can put it back.). Smoke coming from anywhere is never ‘okay’ in a vehicle, you may just have some spilled fluids on a hot engine surface, or some oil that splashed into your wheel assembly or picked up a grocery bag with your exhaust… No matter – get it checked, be sure.

(7) BURNING RUBBER

WHEN: You are not accelerating like the Fast and Furrious.

THE CULPRIT: Your vehicle’s DRIVE BELT is hot, too hot. It is the belt you smell; however, it is caused by something else. Something driven by the belt (like the alternator or tensioner) is creating sufficient friction to make the belt smell like it’s on fire. Do not drive until this condition is corrected or it will not be a choice.

(8) BURNT PAPER / BURNT POPCORN

WHEN: At all speeds, particularly when working your way through the gears.

THE CULPRIT: The CLUTCH facing is burning off as the clutch slips. The odor is reminiscent of smoldering newsprint: like trying to burn the Sunday newspaper all at once in the fireplace, especially if it’s been used to wrap sardines. The friction material is actually a paper composition, which explains the papery part of the smell. Either replace the clutch, or learn to stop riding the clutch.

(9) HOT OIL

WHEN: Your engine is hot.

THE CULPRIT: OIL is leaking onto the hot exhaust manifold. This is an acrid, burning smell. It’s earthier and more nose-wrinkling than the odor of cooking oil used for french fries. If it’s from a leaky crankshaft seal that’s spraying oil all over, some of it will find the red-hot manifold–but most will be on the pavement. A leaky valve cover won’t necessarily leave a drip on the floor if all the oil drizzles onto the exhaust, vaporizing immediately. Locate and eradicate the leak.

(10) BURNT CARPET

WHEN: After you’ve been using the brakes a lot, or hard, or both.

THE CULPRIT: The BRAKE PADS are overheated. This is perfectly normal after riding the brakes coming down a long mountain pass–but you should learn to downshift, you flatlander. If you smell this under normal driving conditions, you’ve got a dragging brake: a seized brake caliper or perhaps you left the parking brake on. If you check the temperature at each wheel, the hot one’s probably the smelliest.

(11) BURNT TOAST

WHEN: Any time.

THE CULPRIT: An ELECTRICAL short circuit or possibly the burning or melting of the insulation around the affected wires, fuses, or connections. If there are any secondary signs, then you should not run the engine until a qualified technician resolves the issue. Left unchecked, electrical shorts can affect many of the systems in your vehicle.