T-stat shouldn't have an air bleed hole in this application. None of the "good" thermostats have the bleed hole, including any that you buy from the Volvo dealer's parts desk (or VW/Audi). It's not missing, rather it's not there by design, not needed due to the design of the system, having the t-stat in the lower rad hose rather than the upper hose means that the engine can be filled with coolant from the radiator (or expansion tank) through the open upper hose without creating an airlock. Only need that bleed hole if the t-stat is on top, so that air can escape from the high point while the engine is filled through the bottom hose. The way these motors are laid out, even with no bleed hole, the only part of the system that won't get filled as you pour coolant in (assuming you follow procedure for disconnecting a hose to vent air at the top of the motor) is the part of the lower rad hose that turns upward towards the motor, about a foot of hose from that turn to where it meets the t-stat housing. Drilling hole makes no difference, won't help though I guess doesn't hurt either. I suspect that the crappy Stant tstats just have it because they are also used in a jillion other applications, some of which may have the t-stat in a different position on the motor...
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