I purchased a heater core from FCP Groton and it came in at a total of ~$145 which was fine. The brand of core I received was Nissens and when I was swapping them I noticed a few differences that (as a mechanical engineer) I didn't want to ignore.
1. The Nissens brand was a bit narrower (~.25" per side) which would allow air in the sarcophagus to flow around the core and thus heat less. To remedy this, I tore the foam liner off the old core and taped it on top of the new foam on either side. (I used small duct tape loops in between but perhaps a glue like hot glue would have been better) This widened the core enough that not much air could flow around it.
2. The Nissens core flange did not fit flush when installed within the sarcophagus. Instead it warped around the screws a bit which allows a significant amount of air to leak out of the sarcophagus instead of through it to the vents. Since I didn't feel it important to warm the cavity behind the instrument panel, I taped strips of duct tape around the flange joint. This sealed it up very nicely. I immediately noticed a boost in the air velocity from my vents.
3. The Nissens heater core came with 2 o-rings from FCP Groton that looked to be viton or buna-n rubber. However, I didn't know they were included. The website suggested I would need o-rings to go with core so I purchased their silicone rings as well. Upon dis-assembly I found that I only needed 2 o-rings. I used the silicone o-rings and threw away the black rubber ones because silicone is a better high temperature material. If you are short on cash and don't want to waste money, you can surely use the black rubber rings and not purchase the extra silicone rings like I did.
Finally, after 2.5 hours of labor (I am a slow/deliberate mechanic
) my car is now pumping piping hot air out of the vents and I can't wait for sub-zero weather. No more smelling of AF either. This install was really as easy as everyone suggested. I'm so thankful to Volvo Forums and its community for sharing so much information.
Happy Heating!
-Sven
P.S. - For those that don't have shop air (like me) you'll not be able to blow the fluid out of the core. Therefore, I used a new (i.e. no holes) trash bag and put it around the bottom of the core when I separated it. This worked like a charm as all the coolant (maybe a quart?) ran into the bag on the driver side floor and I didn't get a drop on my car.
