When your car starts making a strange new noise or emits a strange new smell, it’s not necessarily something major. The first thing to do is calm down and not assume the worst. The second thing to do, if you’re not mechanically inclined, is to find someone you trust to have a listen.
One common and alarming noise that modern cars often make that isn’t usually something to worry about is an exhaust rattle. It’s probably not a death rattle. It’s a good bet the catalytic converter heat shield (a thin piece of metal tack-welded to the converter’s body to prevent its very hot surface from touching and possibly igniting dry leaves and such underneath the car) has come partially loose.
When it does, it makes an obnoxious racket and if you don’t know about the heat shield’s propensity to work itself loose over time you might think there’s something badly wrong.
The fix is as easy and cheap as having someone who can weld tack-weld the shield back into place or (field expedient) just pry the thing off. This will not affect the car’s function or emissions in any way.
Just remember not to park over dry (and tall) grass until you can get the shield repaired.
Rising smoke is another blood pressure riser. But it might be something that’s more of an aggravation than cause for alarm. Unless you drive an electric car. In which case, leave the car at the first sight or whiff of smoke. Lithium-ion electric car batteries can and sometimes, do spontaneously combust. And when they do, they burn fast and very hot. Stop the car, get out, and get away from the car.
If it’s not an electric car, smoke is probably the result of an oil seep or a water leak. The seep (as from a leaking valve cover and then onto hot metal engine parts, which makes the smoke) is usually nothing serious. Pop the hood, see whether you can source the smoke back to the seep. If you see a little seepage around the edge of a valve cover or intake manifold, you can probably keep on driving. But make sure you check the oil level first (seeping oil is leaking oil) to make sure your engine isn’t running low on oil and check it again, regularly until you can get the seep fixed.
If it’s a steady drip look underneath the car with the engine running. You will want to stop driving the car because that indicates significant and possibly even pressurized leakage that could quickly result in the engine running low on oil and then not running at all.
Or the transmission if it’s an automatic. Running an automatic with low fluid can destroy it in just a couple of minutes or even less, if it’s a big leak.
Don’t risk it. Park it.
If it’s a slight drip (there’s no large puddle under the car) it’s probably ok to continue driving, cautiously, so long as you are vigilant about checking both the progression of the leak and the level on the dipstick.
Also be sure to scan your gauges especially your oil gauge often. Any change in reading is cause for immediately finding out why and pulling over. Turn the engine off. Never run an engine with low oil or an unknown oil level or an oil gauge that’s reading erratically or unusually.
Water smoke is more like steam and is usually the result of a leak in the cooling system—the radiator, the rubber hoses that carry coolant from the engine to the radiator (and back to the engine) and smaller hoses that warm up the throttle body in some cars with fuel injection — and so on.
The main worry with coolant leaks isn’t the leak per se but rather overheating the engine, which can cost a lot more to fix than replacing a bad radiator or a hose that sprung a leak. And the thing about most coolant leaks is they are pressurized leaks; which means a small leak is likely to become a big one if not dealt with promptly.
Try to get home or to your mechanic’s place as quickly as possible, but as gently as possible. Drive the car gingerly, to reduce the load on the engine and thereby the heat the cooling system must dissipate. Keep the revs down, which keeps the cooling system’s pressure down. And watch your temperature gauge. If it starts reading hot, that’s your cue to pull over before you cook your engine.
If you see or smell steam inside the car, you have a more serious problem. Your heater core is probably leaking. The heater core transfers engine heat, via warm coolant, into the car’s cabin to keep you warm. When it leaks, it also wets—the carpet, ductwork and so on. It’s not usually a gusher, which means you can keep on driving (making sure to watch the temperature gauge and when the engine has cooled down, check the coolant level and top off as necessary, to make up for the loss).
But you’ll want to stop driving as soon as possible and get it fixed, because the longer it leaks, the wetter your carpets will become and the funkier your car’s interior will smell.
It’ll take a whole box of Mr. T air fresheners to deal with that!