Define "smoke." White smoke -- steam, typical of a coolant leak or condensation from cold exhaust system -- or blue or black smoke, typical of an oil leak in the engine or turbo bearings? At 100K miles, I'd suspect turbo bearings are just starting to show some wear.

I'd also suspect that your missing coolant has nothing to do with a head gasket. These cars are notorious for going through heater cores -- I've replaced two so far, meaning I'm on my third core at only 80k miles. Fortunately, they're cheap ($160 at fcpgroton.com) and fairly easy to replace.

Another thing to check out is the upper and lower radiator hose clamps. My upper hose clamp started to leak at about 60k miles, and it took me a while to find that slow leak before I replaced it with a $2 clamp. The lower clamp just went at 80k miles, but at this time I know that the OEM clamps are starting to fail on these cars, so I replaced the remaining three clamps on the two hoses and I have no more leaks.

--
Jim Rothe, '99 S70 T5M,
http://www.jimrothe.com/volvo/index.html

Because these engines have a sealer instead of a conventional gasket, I would say no. But your car is only two months old to you, so I may have overheated with the previous owner.
If you cannot find the source of the steam, take it to a reputable garage and let them pressure test the coolant system.

Klaus
--
(1975 164, 1995 854T, 1998 V70R)

Water usage not normal. But lots of places it could be leaking from. Pin hole leak between radiator & AC coils would be hard to see, bottom hose also hard to see & get to.

How much and how ofter do you have to refill?

Compression test wouldn't hurt, but also take a careful look around for any greenish stains on/near all coolant lines. When engine hot look close for any steam (I like to do at night with flashlight)

Good luck! Hope it is something simple.