Heater core leak. Fill the overflow tank with distilled water and drive. Fortunately, it is a cheap repair if you grab one of the under $50 heater cores on Ebay. Expect a shop to charge about 1 hour of labor, DIY is about 2 hours.

We don't know how fast the coolant is leaking, I would suspect it is very slow. It doesn't take much to fog up the windows in cold weather.

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Keeping it running is better than buying new

Hi Kevin, I hope your daughter (and her car) made it home safe.

You got good advice, IMO.

From where you and I sit it's hard to tell the severity of the problem in your daughter's car. At risk of making assumptions about your daughter but isn't is a "fun" challenge to try to diagnose cars over the phone with someone who isn't quite so mechanically inclined? Gets me every time.

I'll add that I've limped along with a slight heater core leak for quite some time in a couple cars (thank goodness for that low coolant level indicator). Each car would go a few weeks between needing a top up and only display a strong coolant smell when the heat was on. No steamy windshield but a heavy haze that needed to be wiped clean after a couple months.

The third heater core leak I experienced was a failure at one of the O-rings that gushed fluid and caused overheating in the summer. That got fixed right away.

If it's not losing coolant too fast she is fastidious about keeping the level up, it may be OK until your next visit.

Best of luck,
Will

I would probably try driving it but with the coolant cap loosened a bit to relieve any pressure, even if it wants to spew a little coolant out from under the cap. This time of year she probably doesn't need the system to be pressurized. Heck, it sounds like it isn't holding any pressure anyway.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (STILL not road worthy!)

Similar situation happened with daughter’s 2000 V70 several years ago at 195K. Leaky heater core (inside the central lower dash area) is likely the problem. Heater core slowly leaks coolant into the HVAC ducting and steams up windows. Barring no other issues, car can be driven safely with coolant tank kept topped off. Keep a close eye on temperature gauge and low coolant light. Repair will be a new heater core and o-rings. Check condition of heater hoses too.

She has to be careful. Sounds like a heater core failure
In my 850 I got a puddle of boiling fluid on my shoe and got a nasty Hot foot.

If she refills, then better not do it until the engine has cooled
and better have an antifreeze mix. Can't refill with H20 if it's below freezing.

This is probably when she should have AAA