What can cause white smoke from the exhaust?

Here are the best answers compiled from s.com contributors:

  • It often means that you are burning antifreeze. You asked if it needs antifreeze, have you noticed any leaking out of the reservoir tank while you are running it? Sometimes when the head gasket goes it will produce a passage for the antifreeze to pass from the capillaries into the combustion chamber. It is easy to check if you have an air compressor. Remove one of the rear sparkplugs and the radiator cap. Fill the radiator and then push some air into the sparkplug hole (get a good seal in case a valve is open). Repeat with all the cylinders and watch for air bubbles coming up into the radiator. If bubbles come up or fluid is pumped out, the head gasket is blown and must be replaced. It is more likely to happen at the back of the engine because it is farthest away from the fan and therefore gets less cooling. Also check your oil for discoloration. If it is a brownish color it could mean your oil and antifreeze are mixing and has the potential to damage your bearings.
  • If the exhaust billows white smoke for a few seconds when first starting the engine after it has been sitting for a while, such as overnight, and then runs normally, it could mean that the rubber valve stem seals have perished - especially if the vehicle is a few years old and has done over 60/70,000 miles. Another clue is: does the exhaust smoke smell like fresh, rather than burnt oil.
  • After going nuts trying to figure out sporadic tailpipe smoke on my Nissan Maxima, with no other negative engine symptoms, I eventually stumbled upon a malfunctioning PCV valve. The ball-check wasn't fully seating, allowing small amounts of oil to sneak past and into the combustion chamber. A cheap and easy fix.
  • White smoke or semi white can be produced in several ways. One way is oil this is normally a whitish blue to blue smoke and has the apparent smell of oil being burned. Next could be antifreeze when it is being burned it has a sweet type of smell and tends to dissipate in the air rather quickly. Next is automatic transmission fluid which is normally found on automatic transmissions and its normally drawn into an engine thru a vacuum line via a defective transmission modulator valve or some other defective part. Transmission fluid is very apparent and billows out so bad that you can't see anything behind you. Last but not least another type of smoke that is not white but black is the presents of to much gas/fuel being burned in the engine. PS the one good thing about transmission fluid being burned is it is an excellent way to clean the carbon out of an engine.
  • Black smoke is burning oil. Blue smoke is usually transmission fluid due to a leaking modulator valve in the older auto transmission. White smoke is due to water getting in to a cylinder from a bad gasket, cracked block or a cracked head. cracked heads. Mine started misfiring, with new plugs. Smoke came out the exhaust. Result, low compression in the cracked head. When car was cold it ran fine. After it got hot, the crack in the head would open up, hence, sputtering. I've had to replace 3 heads. Everytime I've had to have this done, I had to buy a whole new head gasket.
  • After extensive research I came to the conclusion that TOO much oil is also a main culprit for white smoke out of the exaust.
  • I changed the PVC valve, the breather and the air filter and it's good as new.
  • There are a lot of incorrect answers here... but for the most part, you can hold true to these: Blue smoke is primarily from internal engine wear. If it's constant when the engine is on, then the rings etc are worn and need to be replaced. If it only is blue when the engine is cold or first started, the rings are worn but not gone completely. You get the oil seeping during the night and it burns off when the car is started in the morning. Black smoke is a fuel/air mixture suggestion problems with injection or carburation. Cause of black smoke is due to running rich in the fuel air mix. White smoke can and DOES come from coolant burn off in the oil due to a leaking or blown head gasket, cracked head etc. If you aren't sure or you don't know what you're talking about, don't advise. Wrong advice can be more damaging than the actual problem.
  • White smoke is caused by engine coolant/Antifreeze being processed in the combustion chamber(s) of the engine.....ie burning, melting, frying, whatever....Period....I'll explain further.... This is automotive chemistry 101....Oil of any automotive type burns blue.....too much fuel issues burn black not enough fuel issues burn grey on a cold day you may see what appears to be white smoke from the exhaust that will disappear after the vehicles engine has warmed up to it's normal operating temp.. This is a normal reaction called condensation... condensation is the result of a small amount of water/dew being drawn into the exhaust usually collecting in the muffler and/or the catalytic converter and is caused by our friend mother nature..... like when you see your breath on a cold day...
  • I am a highly experienced ASE certified automotive repair tech. I have over 16 years of diagnostics and repairs to my credit..I have made a very good living in the automotive business by being precise with my diagnostic procedures....I have worked for 3 of the largest rental vehicle companies in the country.... I have diagnosed and repaired an estimated 200 vehicles to date with the white smoke issue... every vehicle that i mentioned had engine coolant/antifreeze entering one of the combustion chambers in the engine... Most of these vehicles had a damaged head gasket(s).. the most common causes of this issue that i have detected over the years are due to improper maintenance of the engine cooling system, severe overheating of the engine, improper tightening of the cylinder head(s) during an engine overhaul,or some other type of repairs that required the head to be removed and also defects in manufacturing of the gasket or the engine... i have seen evidence of careless repair techs that have scratched or cut the surface of a replacement head gasket with either a tool or the cylinder head during the install process.. sometimes it will never cause an issue but it can... i am very careful when dealing with any gaskets but especially head gaskets due to the amount of work involved in replacing one on some vehicles.. bottom line, I'm not fond of doing the job twice so I'm careful the first time... I have seen improper cylinder head or engine block servicing techniques cause failure of the gasket(s) these types of failures are generally caused by improper cleaning of the gasket surface of the engine block and/or the gasket surface of the head.. i have also repaired or replaced cracked heads and in extreme scenarios i have replaced cracked blocks and severely overheated engines with a new or re-manufactured engine due to such severe damage to the internal engine components or block .. There are a mix of correct and incorrect answers to your concerns by the participants that have replied.. I can assure you that almost every well trained tech will answer your questions as i have.. I'm not saying I'm an automotive god, I am just proud of the priceless knowledge that i have acquired...FYI, I'm a graduate of Denver Automotive and Diesel College in Denver Colorado.... DADC is one of only two Automotive Technology colleges in the country with the intense hands-on and classroom teaching practices to properly train a truly, highly skilled automotive/diesel tech who can easily handle any diagnosis and proper repairs of yesteryears and today's automobile technology....
  • White smoke CAN be caused from oil....I have fast-road engined 1987 Golf Mk II. If I boot it hard on tight corners, roundabouts, etc, it can cause oil surge in the engine and some oil can 'slop' into a cylinder. The James Bond style smokescreen it produces can be very exciting for drivers behind me!
  • Lots of good answers; I just want to see if I can clarify from my experience. SMELL!! Good mechanics without great diagnostic tools learn to SMELL. "Burning" (yes, technically it's boiling, not burning) Antifreeze smells 100% different than burning OIL. Let your nose be your guide. The Antifreeze will have a sweet sort of smell--hey--kinda like antifreeze smells, and it will make your eyes tear up and your throat lungs will tell you to get out of that toxic fog right away. Also--the timing. Yes, when forming a good question, you need to give GOOD DETAILS. Does it ALWAYS burn white? Just at startup? Only when hot? Etc. DESCRIBE, DESCRIBE, DESCRIBE!!! A head gasket problem is ALWAYS there and it only gets worse under pressure/acceleration/load. It will go from a little cloud to it's own weather system when you stomp on the gas.
  • OVERFILLING THE OIL will produce this white burned smoke too. Yes, it will SMELL different. IT will also usually go away after some driving. CHECK THE DIPSTICK, it's obvious, but do it--do it right. Flat surface; cold engine. Pull--Wipe it off--put it in--now you are getting the real level. Oil burning will be at startup from worn valve rings/seals and during driving from overfilling at first a lot, then only at heavy acceleration/g forces when demand is high. Again--smell, check all your fluid levels (OIL, WATER, TRANS) of course, whatever is low is what you are BURINING (or for the one gent that gets particular, boiling). ALWAYS Start w the simplest thing or the cheapest. Did you just change the oil and it started--overfilling, etc. Yes, it won't hurt to check the PCV valve and tubing. Really, check all you can check.
  • My problem with white smoke was whenever I would be going down the road at high RPM and let off the trottle. Then it was like a smoke bomb went off. Bottom Line.......... My Vacuum Modulator went bad on my transmission whenever high vacuum was created it was sucking transmission fluid into my intake manifold and thus into my combustion chamber creating white smoke. Replaced the modulator for $12 and everything is right with the world
  • i had the exact problem with my Mazda down to a T. All we had to do was buy a bottle of engine sealant... it takes a full day to run thru so follow directions exactly. Now the car has no problems... full power is bacl no more "smoke bombs" and no more dying at strange times.
  • Steam or smoke is the question here. If its steam some considerations are what year is the vehicle newer catalytic converted cars emit steam and water from the exhaust and you should be cautious about the blown head gasket or cracked head syndrome, if you suspect a blown head gasket or cracked head go to a reputable shop that can confirm exhaust gasses in the coolant. You will notice a low coolant level and a peanut butter looking substance on the oil cap (possible traces of water and coolant in the oil but generally engine pressures will prevent this. Be prepared for the worst and hope for the best. If it is smoke a thick white smoke it could be transmission fluid being pulled up through a vacuum line to the intake manifold and being burned, this was quite common on older Ford and Chrysler vehicles that had a vacuum shift solenoid and an automatic transmission.
  • Has your car severely overheated recently? Does the smoke smell like antifreeze? If it does, you probably have a blown head gasket. The "smoke" in this case is actually steam from water leaking into the cylinders. Also check for yellow or white goo on the oil cap and dipstick, indicating water leaks to the oil.
  • Your symptoms are indicating a possible head gasket problem. You have water going into the combustion chamber and coming out the back tailpipe as steam. You may also have exhaust gas in the water which can also be checked by a mechanic. Be prepared for the expense of a head gasket or possible engine replacement.
  • If it is not happening all of the time at operating temperature (head gasket as mentioned before) and it occurs just at startup. It may be that due to heavy moisture in the air, dew, a heavy rain, will build up moisture in your exhaust system. At initial startup until the vehicle is warmed up and run for a bit, you may see thick white smoke.
  • I had an old engine that sucked oil through an intake valve when the engine went fast enough. If you burn enough oil it looks white. Especially in Michigan on a cold morning.
  • I had this problem with my '96 Ram after an overheat. A cracked head gasket was allowing antifreeze to get into the combustion chamber and creating all kinds of white 'sweet smelling' smoke.
  • White "smoke" in cold weather is just steam. When gasoline ignites it produces quite a bit of heat and expands to several times the original size, creating high pressure on the piston. That pressure causes the piston to move down, turning the crankshaft which makes the car go. When the fuel ignites it causes a sudden and violent chemical reaction between the the oxygen in the air and gasoline (which is a long chemical molecular chain of carbon and hydrogen) resulting in carbon dioxide and water vapor. As the water vapor cools in the exhaust pipe it starts to form small droplets that are visible in the form of steam vapor. That's the white smoke. Once the exhaust pipe warms up sufficiently, the exhaust leaving the pipe is still hot enough that the water vapor hasn't formed the droplets and dissipates quickly enough that you don't see the vapor. On the other hand, if it's light blue or blue-grey smoke and it doesn't stop when the exhaust pipe warms up, that's oil vapor and a sign of bad rings and/or valve stem seals.
  • white smoke is usually caused by condensation in the combustion chambers. This will usually dissipate once the car has warmed up. If it persists there could be difficulties with: Problem: Solution: Moisture in fuel Apply one cap full of Methylated spirits to fuel tank (This is quiter safe by the way, it dissipates water) Head gasket leak Replace head gasket, approx $500 AUS (other symptoms such high temperature will also be prevailent.) Failing these two suggestions, there is a slight chance of moisture in the oil sump. this is rare if the head gasket is ok. Simply check your oil level, if the oil looks milky, there's the problem. Also if it is milky, replace the head gasket.