My previa loses antifreeze and it emits smoke or vapor from exhaust

most cars I work on drip out the exhaust on the floor alittle when we jack up the front end-Ithink this could be condensation-but if you have white smoke and a sweet smell with it -it could be antifreeze leaking into combustion and going out the exhaust-hopefully not-cheers Denny

could be the head is cracked.
do you have smoke or steam coming out the exhaust?
how is the coolant level?
this engine WILL NOT tolerate running with out coolant.

Sounds like either a blown motor (rings need replaced) or a bad head gasket or cracked head.
If the rings are bad your car would have felt like it was losing power because the engine will no longer have the same high compression that it's required to turn the wheels. You may have heard your engine knocking or seen a light blue colored smoke coming from your exhaust as a result of your engine burning up oil in the combustion chamber from the rings leaking.
If your head gasket is leaking or your head is cracked you'd likely find milky looking oil when you drain your oil from water/antifreeze being mixed in and noticed a white smoke coming from your exhaust that is actually water vapor coming through the exhaust.
If your car was running rough when you last shut it off try pulling all of your spark plugs and either cleaning them or replacing them all. A bad head gasket or bad rings can both foul spark plugs. A car will run rough with 1 or 2 fouled plugs, but once enough foul it will no longer run at all just sit and crank over. If changing the plugs get's it started for ya, check your tailpipe first for water, if nothing, change your oil. If no signs of water/antifreeze or milky colored oil then it's probably rings.

You have a head gasket leak. The gasket is allowing heat/exhaust to pass from the exhaust ports to the cooling jacket (antifreeze). This makes the coolant grimmy. As you move from traffic to park the car, there is no more exhaust gasses pressurizing the exhaust ports and now the hot, pressurized coolant is allowed to move from the cooling jacket into the exhaust port, turn to vapor and escapes through normal exhaust routes.

-Mark

If it doesn't smell like sweet then you most likely got a bad tank of gas. Just to be safe keep an eye on your engine temp. and coolant levels.

White smoke indicates that a possible leak of antifreeze through the head gasket exists, or a cracked block or head. Usually, it's just a head gasket.

Good luck on this repair.

Sounds like head gasket leak into the combustion chamber or a cracked head which does the same thing.

Water vapor coming out of the exhaust at initial start-up is normal; that is condensation that collects when the engine is not running. White smoke at start-up depends on a couple of things. Tell me, where do you live? When the weather is very cold, all engines will emit steam (white smoke) when they are first running; this stops after the engine has been running a while and is warm.

In short, if this is only happening at first start of the morning and goes away over time, there is nothing wrong.

If, however, the "white smoke" continues and never stops, you may have a blown head gasket.

hardly likely the exhaust job would cause that, but yes it sounds like you got a blown head gasket. badl lock stricks hmm! also preasure test cylinder head for leaks

white smokes means you are burning antifreeze. May have cracked head gasket, leaky pcv valve, or too much oil