Ethylene Glycol...the flourescent green stuff...NOTHING ELSE...no pink stuff, brown stuff, blue stuff or brown stuff. It comes under many different names and must be phosphate free. Many swear by Zerex G05 but Prestone is fine...just make sure it's not their Propolyne Glycol alternative (what's good for the environment and animals isn't necessarily good for your Volvo).

Volvo recommended this on 850's then suddenly they had their own stuff that somehow is so much better (rolling eyes) and nothing else can be used but it (rolls eyes again). As long as that mechanic used the flourescent green stuff, your wife's car is fine. If you ever do a flush you can switch over too.
Some people swear by the Volvo stuff but I've never heard of trouble from Ethylene Glycol antifreeze. Btw, now on the bottles it says "will not harm aluminum engines." That's what you need to read on the label.
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1998 S70 T5 Emarald Green Metallic (125K), 2004 V70 2.5T Ruby Red (45K), Previous Owner of Black '94 850 Turbo Wagon (Sold at 140K and miss her). My cars have been running so well lately they've got me worried.