The Volvo torque spec for the water pump fasteners is a nominal 20 nm, approx 15 ft-lbs, which is by no means excessive or anywhere near the yield point. Any bolt that snaps at 16 ft-lbs was likely badly fatigued from previous over-torquing or your torque wrench was incorrectly set or badly out of adjustment. New nuts and a bolt are often supplied with new water pumps, which does suggest these fasteners can be a problem area, but I've never hesitated to re-use the original Volvo hardware, especially as I know who the preceding mechanic was (either me or the factory).
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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