When I installed the new t-stat in my parents '98 V70 this past Monday, I noticed something a little odd. The old t-stat was installed by the dealer like this: http://www.matthewsvolvosite.com/images/removing_tstat_bolts.jpg. The breather valve was in the front to the left of the arch. From what I read, it is important to have the breather valve in the front. The only way for the new Volvo t-stat to have the breather valve in the front, looking like the "old" installed t-stat, was to have the breather valve on the right (if you are looking at the t-stat from the front of the car) of the arch. Also, the arrow on the arch is facing back towards the firewall. I don't know why it would matter, but thought I should ask. I also went ahead and replaced the coolant temperature sensor with a new FAE sensor. Not to mention new upper/lower radiator hoses, new upper/lower expansion tank hoses, new expansion tank and cap, and of course Volvo coolant. Thanks for the help!

Regardless of what car it is, the bleeder (whether it's an actual ball valve, or simply a small hole with a jiggle rod in it) must always be on the highest point on the rim. Only when the rim is perfectly horizontal doesn't it make a difference -- but even the slightest tilt, however, compels the aforementioned specific placement.

This is simply because air bubbles float in liquid, and therefore they will congregate and fuse into an air pocket at the highest spot under the thermostat -- where the bleeder would let them readily escape to the top of the thermostat where they can return to the radiator and be purged through the hose to the overflow tank.