Firstfives.org

Happy Friday all. Have been rebuilding Evelyn’s heater and evaporator boxes. Slowly, laboriously acquiring assembling new e28 evap and fan, hoses, hard-to-find foams, etc. Reassembly of the heater box was nearly complete when I installed the famously unobtainable heater water valve using new factory o-rings (or at least, bought from the dealer and bearing the correct part number on the package), only to find that they didn’t quite fit in the recesses of the valve housing. Figuring BMW knows better than I do I tightened the famously inaccessible nuts onto them anyway, only to find out a bit too late that they don’t allow the flange mating surfaces to meet. The heater core flange in particular, being made of plastic, started to bow around the o-ring. The metal pipe next to it was more willing to mate, but in the process literally pulled the valve apart — upon testing it leaked at the inboard seam near where the bolt is embedded.

I was pretty sure I was going to have to just block off the entire heat mechanism, as these valves appeare nowhere on the planet. Except, that same day, on ebay — some fellow clearing out old inventory from his restoration shop had a new in box copy, complete with new nuts and o-rings. I didn’t negotiate. Upon trying to install the new valve, I get the same reluctance to fit cleanly, the same bowing, and of course I have stopped way short of tightening down.

So what genius at BMW thinks a 17.12mm inner diameter o-ring is the right solution here? Or what am I doing wrong? Measuring with my cheap Chinese calipers, I actually have these rings at 17.5 ID, 21.7 OD and 2.5 CS. So they’re a bit large, maybe? Interestingly, the ones I bought from the dealer and the ones (easily 10 years old?) from the ebay seller, which clearly are part of factory kit, are exactly the same size. So I don’t think they’re a fluke? I have used plumber’s grease to ensure maximum complicity from the parts, but I am not willing to blow up another valve when they’re so hard to get, and so am thinking about alternative o-ring sizes.

Has anyone taken a scientific approach to this? Thoughts? How did you win? Btw, I think I may be able so squish some epoxy into that seam on the kaput valve and keep it for a spare. Also interested to know if anyone has tried that with any success.

How do your new o-ring sets compare to your old o-rings, assuming you still have them?

So I found another valve, bought a bunch of orings, and tried tightening the second valve over a 17x2.5mm (as opposed to 17.12x?). The result? Leak at exactly the same place. Both these valves were manufactured in ‘79m btw. I scared up yet another valve, this one mfgd in 1985, and used a 16.5x2.5mm oring. It sat nearly flush with the valve surface, but unlike the others fit comfortably inside the valve seat. As a precaution I tightened the core to the valve first — that part of the valve is not under the same stress as the upper flange that mates to the metal pipe. Then I partially tightened the metal pipe flange at first, c-clamped the valve snug near the upper flange, and let it sit overnight to settle the oring a bit, then tightened it flush the next day. It tested ok with water pressure up to 20 psi, which seemed enough.

All this in the process of rebuilding the heater box top to bottom. If I could figure out how to post photos I’d show it off. With this last touch, the heater box is ready to install. Thanks to Bob Bondi for his suggestions on some of the stickier bits of the project.

Only a minor contribution to the discussion; orings need to be lubricated before installation, a minor scuff can easily lead to annoying leakage.

Make sure the lubricant is fully SYNTHETIC. Like bases are solvents for each other, so don’t use any petroleum grease or WD-40 stuff. Even if the oring is petroleum compatible, better safe than sorry.

When I replaced my heater valve last year I used the O-rings that La Jolla Independent included when I bought it. I lubed them with Molykote when I installed it. (I've learned the hard way about lubricating o-rings, when I pulled injectors on my SE-R.) Sealed up with no problem.