It's believed that engine block porousity plagued a small number of 92 and perhaps 93 960 for sure. There have also been other model years reported, but certainly by 95 it had been addressed. It's prevalence is not known, however, since Volvo basically denied it. and never stood behind any claims, to my knowledge, execpt to offer block replacements at a good price, as I recall. The newest model years, 97/98 V/S 90s are good cars, in my opinion.

If you suspect the problem, visually check the exterior of the block for patch attempts. If you are deciding on a specific car, have the cooling system pressure tested for about 2-3 hours on a cold engine.
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John Shatzer, '97 V90 @ 98K