Wispy white tailpipe smoke... first noticed it months ago but it would go away, blamed it on cold weather. Now I've watched it a while and find that while idling, it disappears as soon as the automatic fan comes on, then reappears as soon as the fan stops. No overheating recently, no other symptoms I've noticed. Fan cycles on and off at intervals of a couple minutes while idling. Could this be related to the thermostat? Hoping it's not a head gasket, but the smoke is not thick, dissipates into atmosphere within a couple feet of the car.

3.0, 199k miles.

 

Are you having to fill the coolant bottle fairly often? Get down close and smell the vapor, is it sweet smelling?

If the exhaust smoke is white:

Does the exhaust smoke quickly dissipate after leaving the tailpipe? If so, it is probably the result of condensation building up within your car’s exhaust system. This is a common sight when cars, even modern ones, are first started in the morning. If it continues well after start-up, then you may have serious trouble. White exhaust smoke often happens when an engine burns coolant that has leaked into the combustion chamber. The following are the most common culprits:

• Blown head gasket: This is not so great news, but your engine’s structural integrity has most likely not been compromised, so it’s not ruinous. An engine essentially consists of an engine block and a cylinder head. The block is where the cylinders and coolant passageways are located, and the head is where the valves and rocker arms reside. The head gasket is placed between the two to seal the connection. If it is damaged or compromised, coolant can find its way into the combustion chamber. This is a costly, but fixable, issue.

  
• Damaged cylinder head: This fix is more of a Greek tragedy. Most of the explosive action happens in the cylinder head, where the combustion chamber is located. A cracked or extremely warped cylinder head will cause the engine to lose compression and misfire. Why? There’s too much heat. Overheating puts undue stress on all of an engine’s metal components, especially the cylinder head, which is at the center of the heat production in a car. Excessive heat, normally caused by a cooling system failure, can cause the head gasket to fail, which in turn can cause the cylinder head to crack as components warp and pressure builds. This is not an easy fix. Heads have very precisely milled surfaces to provide a smooth and flush fit with all the connecting parts. You’re better off replacing the head altogether. Depending on the age and value of your car, you might consider buying a new vehicle.

  
• Cracked engine block: Call a crash cart: your car engine is dead. As we said above, the block houses the cylinders and their components inside a cooled and lubricated crankcase. It’s cast from one piece of metal – typically iron or aluminum – to be extremely strong and sturdy. It also supports the rest of the engine’s components. Cracked blocks are virtually impossible to repair. An engine swap is the only reliable remedy, but that can be extremely expensive and thus sometimes not worth the investment. Depending on the age and value of your car, you may want to consider cutting your losses and buying a new car.
• You can have a shop check to see if there are hydrocarbon in the coolant bottle. Very easy and very fast which is a sure sign of some failure allowing coolant into the combustion chamber.

• f your car were a diesel, (you're in California so not applicable) it's usually Having white smoke come out of a diesel is normally a sign that the engine is running lean. So, this would tell me that odds are you have an injector that is sticking when the engine is cold and one cylinder is not getting the fuel it needs. This is where a mechanic will be able to test the injectors and tell you which one is your problem.

 

Thanks for the reply! I can add the following by means of troubleshooting/observing:
-Didn't see it all day today when the weather was over 60 degrees. Started to see the smoke in the evening, vehicle definitely warmed up.
-NOT overheated, no smell of antifreeze, haven't had to add coolant in many thousands of miles since I added a new water pump.
-No froth under the oil cap, nothing weird on the dipstick.
-Smoke is thin and white/gray, not billowing clouds.

Someone has suggested to me that it could be a piston ring letting oil past, which gets burned off? I don't have a noticeable loss of power or misfires. Could this just be an old car reacting to cold desert nights?

 

Oil would be blue smoke