Exhaust smoke is one of the few car problems that tells you what is wrong before anyone opens the hood. The color names the fluid that is burning, and each color points at a different system, with a different level of urgency.
- White smoke: coolant is getting into the engine. The one to take seriously.
- Blue or gray smoke: the engine is burning oil.
- Black smoke: too much fuel, not enough air.
- Thin white vapor that disappears: usually nothing at all. See below.
Is smoke from the exhaust normal, or is it just steam?
On a cold Beaverton morning, a thin white cloud from the tailpipe that thins out and vanishes within a minute or two is condensation, and completely normal. Burning fuel produces water, and on a cold exhaust that water turns to visible vapor before the system warms up.
Three things separate real smoke from harmless steam: it keeps going after the engine is warm, it is thick enough to hang in the air rather than dissipating, and it has a smell. Steam has none.
What does white smoke from the exhaust mean?
Thick white smoke that keeps coming once the engine is warm, usually with a faintly sweet smell, means coolant is reaching the combustion chambers and being burned along with the fuel. This is the color to act on quickly, because coolant that is going out the tailpipe is not doing its job of keeping the engine cool.
Check your coolant level and watch the temperature gauge. If the reservoir is dropping with no puddle underneath, the coolant is going somewhere it should not, and burning is one of the ways that happens. A failed head gasket is the cause people have usually heard of, and our car overheating page goes into that in depth. But it is not the only possibility, and it is not one to assume from the driveway.
What to do: stop driving it any further than you have to, especially if the temperature gauge is climbing. Bring it in and we will find out what is actually happening before anyone quotes you a large repair. Related: cooling system repair and radiator replacement.
What does blue or gray exhaust smoke mean?
Blue-tinged or gray smoke with a sharp, acrid smell means engine oil is getting into the combustion chamber. When it happens tells us where it is coming from:
- A puff at startup, then it clears: usually valve stem seals. Oil seeps past them overnight and burns off on the first start.
- Under hard acceleration: more often piston rings, which is the more serious of the two.
- Constantly, at every speed: significant internal wear, and worth diagnosing rather than topping up.
- Along with a check engine light: a clogged PCV valve can force oil past seals, and it is one of the least expensive causes on this list. See check engine light on.
An engine burning oil will run low between oil changes, so check the dipstick more often than usual until it is sorted. Running an engine low on oil turns a repair into a much bigger one.
What causes black smoke from the exhaust?
Black smoke means the engine is getting more fuel than it can burn cleanly. It is the least alarming of the three colors and usually the most fixable, but it is costing you real money at the pump every day you leave it.
Common causes are a clogged air filter, leaking or dirty fuel injectors, a failing sensor feeding the computer bad information, or a fuel pressure regulator letting through too much. Nearly all of these also cause rough idle or loss of power, and most of them set a code, which is why a fuel system service or a tune-up is often where this one lands.
What if the smoke is coming from under the hood?
Everything above is about smoke from the tailpipe. Smoke or wisps coming from under the hood are a separate issue: usually oil or coolant leaking onto a hot exhaust component and burning off there, rather than being burned inside the engine.
That version normally comes with a distinct smell and often a fluid leak you can spot on the driveway. Our car burning smell page sorts it out by scent. Either way, if you can see smoke under the hood, pull over somewhere safe and shut the engine off.
Is it safe to drive with smoke coming from the exhaust?
- Stop driving now: white smoke with a rising temperature gauge, or any smoke from under the hood.
- Get it in this week: white smoke with a normal temperature reading, or blue smoke that is getting worse.
- Book it soon: black smoke, or a small puff of blue at startup that has not changed in months.
- Probably nothing: thin white vapor on a cold morning that clears once the engine warms up.
What can I check myself?
With the engine cold, check the oil level on the dipstick and the coolant level in the reservoir, and note both. Then look at the oil itself: if it appears milky or looks like coffee with cream in it, coolant is mixing with it, and that is worth telling us straight away.
Never open a radiator cap on a warm engine. The system is under pressure and the coolant is well above boiling point.
How do you find what’s causing the smoke?
The visual check is free, and smoke gives us a strong starting point before the car is even up on a lift. We read any stored codes at no charge, check oil and coolant levels and condition, and look for the leak paths that explain what you are seeing. Where the cooling system is implicated, pressure testing tells us whether it is holding.
Deeper diagnosis beyond that is billable and quoted for your approval first. We will not run up a diagnostic bill without telling you. Whatever we find is documented through our Digital Vehicle Inspection with photos, so you can see the evidence rather than take our word for it, and vehicle diagnosis covers how we work through it.
The most useful thing you can tell us is the color and the timing: what color, and whether it happens at startup, under acceleration, or all the time. That pair narrows it down more than any other detail.
Is the repair covered by a warranty?
Qualifying repairs at MotorCar Doctors are covered by a 36-month / 36,000-mile nationwide warranty on parts and labor, honored at participating shops across the country. A few items carry their own terms. Full details are on our warranty page.
Where can I get exhaust smoke checked in Beaverton?
We have been reading what exhaust smoke is telling us in Beaverton since 1995, with ASE-certified technicians, for drivers across Aloha, Tigard, Hillsboro, Cedar Hills and the rest of Washington County.
MotorCar Doctors Auto Repair is located at 13203 SW Canyon Rd, Ste C, Beaverton, Oregon 97005, open Monday through Friday, 8:00 AM to 5:00 PM. Call 503-626-4810, and tell us the color.