Due to a leak at my water pump, following a coolant flush, and my OCD, I'm now going though my whole cooling / heating system in my 1978 FJ40 and have everything taken apart and have a few questions. I've read a few threads on here concerning heaters and cores but haven't found one that talks about what the rear core is made of. Does anyone know what the rear heater core is made of ? I assumed that it was brass/copper and had just been painted silver or pewter or whatever from the factory but when I got it apart, there seems to be some rust on it, not a lot, but some on the fins, and they do seem more sturdy than copper. The cover wasn't really very rusty so I didn't think that the rust on there was just stains from that but I don't know. The pipe nipples don't even look like brass, even on the inside. At first I thought it looked like brass inside but now I think that was just rust and coolant crud in there looking kinda brassy but I'm not sure. I'm wondering because the guy I talked to about boiling it out and pressure testing it said he couldn't do it if it wasn't brass/copper... specifically, he said he couldn't do it if it was aluminum. It really feels too heavy to be aluminum. Is it steel? I took both and rinsed them out, the rear seemed fairly clean, only a few small dark particles came out when I put water in it, shook it around and poured it out several times. The front core was harder to get water to go in it and when I shook it and poured it out it was harder to get the water to come back out and it was rusty and nasty looking every time so I figure it's really clogged up with crap. I put vinegar in them, and let them sit overnight 3 times and the front still seems clogged and has dark rusty crud come out and I think it might even be leaking. The more I have thought about it, it seems like I remember seeing a little coolant in the floorboard last winter and wondering where it came from but just wiped it up and then didn't see anymore and ended up forgetting about it.. I know that sounds dumb but it wasn't gushing out and I never saw any more in the floor so the issue just went to the back of my mind. I'm wondering if it's even worth fooling with having the front one boiled out and pressure tested. I found one on Advance Auto Parts website for $55 (Ready-Aire?), called them up and they say it is a brand new heater core and made of brass/copper... the radiator shop guy told me it would be about $20 to boil out and pressure test mine and then if it leaks and can't be fixed, I'm just out $20 and have to buy one anyway... seems kinda pointless... has anyone on here bought one of these Ready-Aire cores before? Wondering if they are just as good as the OEM one. I'm going to be rebuilding the heater and blower with those kits from AATLAS1X.. having the heater parts blasted and powder coated... might as well have a new core in there if I can I guess... just hope the rear core is ok.. I don't want to have to take this stuff back apart again. Does anyone know if it's possible to put some kind of shut off valves on the pipes to the rear heater in case something happens with it ? yes, that's a big dirt dauber nest in the bottom of my heater... wtf? how they found their way in there, I have no idea.. that thing could've been in there for years... rotten foam core didn't look as bad on the outside as I thought it might still not great though... Can someone tell me what this hose on the bottom of the blower is for ? it's never been attached to anything since I've owned it.. just hanging there. Is it supposed to be attached to something?