you should not mix regular anti-freeze with the volvo coolant as this ruins the long-life properties of the volvo coolant.

Technical tip- use only coolant that is 100% phosphate and silicate free in your 850- and actually any automobile with alumn rads, heater matrix and alum engine components (head/block, etc). To my knowledge Volvo, BMW and Land Rover branded coolant is 100% phosphate and silicate free. Using yellow jug Prestone, which at one time said "good for all metals", just is not 100% free of phosphates and silicates and using any coolant not 100% free will cause corrosion pin holes in your radiator and heater matrix and start corrosion within your coolant passages of your block and head. These repairs can be expensive. The good stuff will cost a little more, but you'll avoid headaches later. You probably already know to change your coolant every two years./HC

Sounds like a good question for the dealer. Mixing coolants should not cause the brown color you discribe. Normally if you flush the radiator correctly, most of the sediment and residue should be flushed out. If your new anti-freeze has a light brown color, then there may have still been a little residue in the system. If the anti-freeze is a darker brown, I would question if the system had been flushed or simply drained and refilled.

Oliver

64 122S
66 1800S
86 245DL
96 850GLT