You understand certain colors when it comes to driving. Green means “go.” Yellow means “caution.” Red means “stop.” Traffic lights are supposed to change color, but what does it mean if your car’s exhaust starts swapping shades? It could mean nothing, or it could be a sign that there’s a problem you need to have checked out. Before your next drive has a chance to “go up in smoke,” review the car exhaust color coding below to help you determine if it may be time for an oil leak repair, an engine tune up, a coolant check, or something more serious. (Psst! If you have a diesel engine, please consult with a technician. The following information is geared towards gasoline engines and may not be appropriate for your vehicle.)

Car Exhaust Smoke Colors

Smoke Color: Light or thin white exhaust smoke
Diagnosis: Normal

Light or thin white exhaust smoke is typically water vapor. You’ll notice it the first time you start your car, especially if it’s a cold day. This happens because condensation naturally collects in the exhaust system. Light or thin white exhaust smoke is common in vehicles.

Smoke Color: Blue/gray exhaust smoke
Diagnosis: Not normal

Blue/gray exhaust smoke means there’s likely an oil leak and your engine is burning oil. Time to have a qualified technician check things out. The leak could be caused by several issues like leaking valve seals, damaged piston rings, or worn cylinder walls.

Pro-Tip: Blue smoke during acceleration means your vehicle’s piston rings may be damaged. During deceleration, however, blue smoke means the cylinder heads’ valve guides are damaged. Either way, something is damaged that shouldn’t be. Help your technician diagnose the issue by taking note of when the blue smoke occurs, then head to your nearest Firestone Complete Auto Care!

Smoke Color: Black exhaust smoke
Diagnosis: Not normal

Black exhaust smoke can appear when the vehicle is burning too much fuel. This could be caused by a clogged air filter, malfunctioning fuel injection system, a blocked manifold, or a variety of other issues. A clogged air filter won’t hurt your gas mileage thanks to today’s automotive technology, says Consumer Reports, but you’ll pay for it with poor performance. Have your vehicle checked out by a technician to see why your vehicle is burning more fuel than usual.

Smoke Color: Persistent, thick white/gray exhaust smoke
Diagnosis: Not normal

A steady stream of thick white/gray exhaust smoke coming from your tailpipe could mean there’s a leaking head gasket. “In this case,” automotive writer Paul Brand explains, “the coolant would end up being heated in the combustion chambers and blown out the exhaust as the engine starts.” A coolant leak in the summer could easily lead to an overheated engine, and an overheated engine could leave you stranded on the side of the road.

Heavy white/gray exhaust smoke pouring from your tailpipe could also mean a cracked block or cylinder head—both very serious problems that should be addressed quickly. Waiting too long could cost you in repairs.

If your exhaust is sending up smoke signals, play it safe and visit the professionals. Your car may be trying to inform you of an oil leak, broken engine part, a clogged filter, or something else. Find your nearest Firestone Complete Auto Care and bring your vehicle in for a courtesy inspection today, and if needed, an important repair!