Why is it that when a car is started and operated in a cold temp (eg 30F) that there is a vapor produced and when it comes up to operating temperature the vapor is no longer evident?
Off to GQ.
Hot engine gases meet cold exhaust pipes, etc. @ start up.
Once the entire system is at a common operating temp, the similar temps don’t encourage vapor/condensing.
The vapor is water vapor.
What Philster said.
Nothing to add, really, except “Welcom to the SDMB, Wildrover!”
Well, you could add a bit more explanation:
As Gary T said, the visible “vapour” is water. True water vapour (steam) is invisible; what we know as “steam” is actually tiny droplets of liquid water that have condensed upon contact with cold air. If you look at a boiling kettle, you will see that the steam is not very visible until an inch or two above the spout, once it has had time to condense. So when the engine is cold, the water vapour is not that hot and will condense out into visible droplets.
That all makes alot of sense to me now. Probably same reason that we “see” our breath, but you don’t see the vapor when you open the front door…
FYI for every gallon of gas you burn a gallon of water is created by the engine and Cat converter.
When you start a car cold this water condenses into visable droplets before it exits the pipe, so you see clouds of “steam”
Once the car is warmed up, the exhaust stays warm enough that this condensation does not occur before the exhaust exits the pipe no visable “steam”
Welcome to the boards
It can also be crankcase oil being burned by an old engine with worn rings. As the (aluminum) pistons heat up & expand they form a tighter seal and allow less oil to pass by. Very low temperatures can exaggerate this effect.
True, Hail Ants, but water vapor has a white coloration while oil burnoff tends to have a blue or black hue.