1998 Volvo S90 Smoke from vents & Temp Gauge Spike

[cableguy]

I've been having a bit of a problem with my 98 s90 Volvo lately. I recently had my alternator replaced on the car and has since been having tons of problems. The latest is the temp gauge spikes into the red and the condensation, misty/smoke like air, coming from the vents. No particular odor. As a backstory, the AC is broken so the only thing I use is the heater when it get's cold outside. On top of that, the coolant sign has been coming on so I've been putting 50/50 coolant in car a couple times. Since it kept disappearing I started putting water to see if there was a leak. I don't see any leaks on the ground, in the exhaust and the oil pain isn't milky so not really sure where it is going. The misty smoke started occurring once I started putting water in the coolant. I've been doing a fair bit of research and the only thing I can think of is changing the heater core per some forum advices. Not exactly sure if that will solve the problem but wanted to get advice before given the specific issues before buying the parts and doing major work.

Thanks in advances for all the tip and suggestions.

[93Regina]

I've been having a bit of a problem with my 98 s90 Volvo lately

Oh, just do a R&R headgasket, and R&R of heater core, and everything will be fine, if nothing has been damaged beyond repair.