Is it a turbo or non-turbo? If it's a turbo, it sounds like your oil trap needs replaced. It's located under the intake manifold. $40 part behind $400 worth of labor but it's better than replacing the head gasket.

For non-turbo it could be the flame trap. You can also check for blow-by on your tail pipe. There might be a thin film of oil on your back bumper or back window on a wagon.

If the PCV system hasn't been cleaned up lately, I would start there.
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Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE

White smoke can also be from transmission fluid, if an automatic.

Blue = burning oil.
Black = gasoline.
White = steam.

If you notice copious amounts of white exhaust during hard accelleration, eventhough the engine has warmed up nicely, then it could in deed be coolant. Normally, if the amount of the white cloud decreases the farther you drive, then it is just water in the exhaust system. There could be up to a quart of water hiding in there.
So, check the fluid level in the antifreeze expansion tank. You might want to mark the level with a black marker. If the level does not go down after a few hundred miles, then it is not a headgasket leak.
I have seen broken turbos on the 700s blow enough white smoke to kill a million mosquitos, similar to the white smoke stunt pilots leave behind. This is oil leaking through the turbo seals and going directly to the exhaust pipe and vaporized, not burned. But, by then, you can hear the turbo clacking a block away! A turbo can be rebuilt for about $350 plus labor.
If you are burning antifreeze, the exhaust will smell funny. And you are probably looking at a new head gasket. The repair is quite expensive.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)