On my 1995 Volvo 960, when first starting it up while cold it smokes for about 3 minutes and then clear up

Could be just condensation bcuz you're not warming it up to operating temperature during the initial start ups-Moisture turns into water in the crankcase

White smoke is a sign of burning coolant and you should see the level in the reservoir dropping over time. If it clears up after a few minutes, the leak is not very bad yet. A leaking cylinder head gasket is the cause.

If you find the coolant level is not dropping, you might just be seeing condensation in the exhaust system burning off, especially if the smoke doesn't appear right away until the system has warmed up. The definitive test would be to add a small bottle of dye to the coolant, drive the car a few days, then check with a black light at the tail pipe. The dye will show up as a bright yellow stain.