re: "...car was runnung hotter than usual and ...."

I really hate to ask you this but how do you know the car was running hotter than usual? Was it because your temperature gauge was shooting up too high?

Reason for asking is that these water pumps, especially on a car as new as a '93, usually don't fail like you (or your mechanic) describes!

Since it's a '93, I'd first want to know if the gauge (actually, the notorious Temperature Compensation Board) is having it's common epileptic fit instead! In a nutshell, this board (a controller on the temperature gauges of '86-93 cars) commonly goes whacky, and makes the gauge lie! I know, because I've got two '93s and this board has had its episodes on both cars! Yet they, and my '84 (not to mention my formerly owned '83 and '80) all never had a problem with the pump -- not that the pump couldn't go bad, but 10:1 odds your problem was a lying TCB instead!
BTW, I've removed the TCB from both '93s, so I can now trust the gauge once more!

Frankly, I would test the actual temperature (a simple RayTek hand-held IR thermometer aimed at the thermostat housing, or at the intake radiator tank, would do) before I believed an '86-on temperature gauge.

What I'm afraid, actually, is that your mechanic started doing work that was unnecessary (water pump, thermostat, etc.).
A mechanic shouldn't say, "if that doesn't work" -- he should know what the problem is, or else he's just guessing.

And one thing, beside the TCB, is that you said the overflow tank was bubbling? The coolant rarely gets that hot, at least with antifreeze. Another, and frankly quite terrible alternative possibility, instead of the TCB, is that you've got a blown head gasket! That would certainly fill your cooling system with lots of gas bubbles that appear like boiling coolant. Your mechanic should have considered this, too. He should have a "sniffer" (chemical detector) that could determine the source of the bubbles.

Hmmm, is your mechanic experienced with Volvos? Does he have a good reputation?

Good luck.