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Smoking Vehicles

Truck emitting smoke

Vehicles and Air Quality

Vehicle exhaust is a leading contributor to air quality concerns. Vehicles and other mobile sources create over half of Iowa’s air pollution! Much of this pollution comes from a small population of poorly maintained vehicles – the easiest ones to spot have visible smoke emissions. One smoking vehicle creates as much pollution as up to 30 properly functioning cars. 

Health Impacts of Smoking Vehicles

The tiny particles and other pollutants in vehicle exhaust contribute to respiratory problems and to cancer-risk. Everyone can be affected, but sensitive populations including children, the elderly, and those with respiratory illness are especially at risk. Cleaning up smoking vehicles will improve air quality to help Iowans breathe easier.  

Performance Benefits

Excessive exhaust is a clue something is not working properly. Since smoke can be unburned fuel, repairs can yield savings of up to 13% at the gas pumps! Other benefits include enhanced engine performance, higher resale value, reduced emissions, longer engine life, and improved air quality.

Bus Emissions Education Program

BEEP, a not-for-profit organization, is a partnership among Iowa's Department of Natural Resources and Department of Education, the School Administrators of Iowa, Iowa Pupil Transportation Association and Mirenco, Inc., an Iowa-based company that specializes in fuel management technology for reducing vehicle emissions. BEEP is the nation's first voluntary bus testing program and helps fund emissions tests on all of Iowa's nearly 5,000 diesel school buses at no cost to schools or state budgets. BEEP officials plan to test all school buses twice a year and offer guidance for lowering bus emissions, saving fuel and improving the health of students.  More information about the BEEP program can be found on the Bus Emission Education Program website.

Probable Causes and Correction

Visible tailpipe smoke can vary in color to indicate different engine problems. Use the chart below to help diagnose problems. This is a guide, and not a substitute for consulting an auto technician:

Gasoline Engines

Visual Signs Diagnosis Probable Causes
White Smoke Low engine temperature
(Usually occurs during engine start-up)
  • No repair needed
  Coolant or water leaking into combustion chamber
  • Bad head gasket
  • Cracked block or cylinder head
Blue Smoke Engine oil being burned
  • Oil leaking into combustion chamber
  • Worn piston rings, valves, or cylinders
  • Bad exhaust manifold
  • Bad head gasket
Black or Grey Smoke Incomplete fuel combustion
  • Cold engine (no repair needed)
  • Clogged air filter
  • Carburetor, choke, fuel injection, or emission system malfunction
  • Ignition timing off
  • Low compression from engine wear

Diesel Engines

Visual Signs Diagnosis Probable Causes
White Smoke Low engine temperature
(Usually occurs during engine start-up)
  •  No repair needed
  Improper air/fuel mixture
  • Faulty fuel injection / valve timing
  • Engine overheating
  • Faulty fuel pump and/or injection pump
Blue Smoke Engine oil being burned
  • Excess engine oil (level higher than normal)
  • Worn piston rings, valves, or cylinder
Black or Grey Smoke Incomplete fuel combustion
  • Damaged air filter
  • Faulty fuel injection system
  • Clogged air filter
  • Wrong grade of fuel
  • Incorrect fuel injection pump timing
  • Engine overheating
  • Low compression ratio