I’m about 2/3 of the way through replacing my heater core on a 1999 SR5. It appears to be the original unit, which is impressive considering it was 20 years old and had been on there for 396k miles. The original post with all the pictures was phenomenally helpful. I wanted to add a few comments for anyone that may reference this thread in the future:
-take the center console out first. You’ll need the room to move around.
-all you need is a T40, 10mm, 12mm, 14mm, and Phillips screwdriver
-probably goes without saying, but don’t forget to remove the hoses from the heater core in the engine compartment. Also, pull out the rubber grommet to reuse later
-having both front seats out gave me a lot more room to move around
-I was unable to completely remove the metal cross member tube like the OP did. There are far too many wiring harnesses strapped to it and I didn’t feel comfortable moving them all. However I did unbolt it on both ends and pulled it back from the passenger side.
-getting the heater box pulled back and rotated far enough to access the heater core is really challenging with the crossmember in there but it’s possible. Getting the factory one out was easier because the short sections of pipe from the core to the engine bay can be disconnected. However, the replacement unit I bought had the short pipes clamped on and it was therefore a tight fit to slide it into the heater box but I eventually got it. The OP showed removing the airbag module (the three T40 torx screws) and I also removed the ABS module to give me a little more room.
-I have the manual A/C controls and i did not remove the climate control unit. I did however unhook the cables for hot/cold and vent/recirculate from where they terminated.
-I laid out a piece of plywood on saw horses and labeled every bolt I took off and noted where it came from. This made reassembly much easier and I didn’t worry about missing anything.
-separating the two halves of the heater box was pretty challenging. Getting them lined up again and back together was even trickier
-there are two metal supports that attach at the trans tunnel. The OP removed the bolts at the tunnel but not at the top. I also removed the top bolts to provide some more room since I didn’t remove the cross member.
-as someone else mentioned, it was a great opportunity to clean all the trim pieces as I went along. The PO was a smoker so there were ashes and grime on everything and I was really able to get things clean.
I still need to get everything buttoned up tomorrow so if I think of anything else, I’ll update this post.
