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Heater valve replacement saga (long) Posted by Arabiflora [Email]  (#1129) [Profile/Gallery]
(more from Arabiflora) on Mon, 15 Nov 2004 22:27:28
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A cautionary but ultimately hopeful tale....
I recently blew the heater valve in my '88 900S (327k!) and went to one of the eSponsors for a replacement. I was faced with a dilemma discussed ad nauseum in these pages: Buy the OEM part at ~$120 or an aftermarket at ~$30. I went for the low $ option, did the R&R, topped off coolant reservoir.
First test drive, I got heat. Crack another cold one and toast the DIY ethic!
Next drive, I got no heat. Bleed coolant system, verify heater hose config at valve, replace $12 aftermarket thermostat with $30 OEM from Saab dealer. Top off coolant, bleed system, drive into the cold Wisconsin countryside... I got no fu%$ing heat.
Both heater hoses warm/hot at operating temp, although input hose hot while return hose only warm/hot after time. I'm thinking that the heater core is plugged, but all messages by Saab-geeks to the forum says that never happens. I disconnect heater hoses and get up-close-and-personal with the intake/outtake tubes. Blow on the intake tube, coolant comes out the outtake... but not a lot, hmmm. Turn heater valve to cold, no coolant.
Let's cut to the chase. I ended up pulling the heater core/valve by removing the knee bolster, etc (again). Separate core from valve, find no evidence that core is plugged (mmmm...antifreeze!). Inspection of valve was inconclusive: parts moved when I turned the gear but there was no way to know if they were moving in the right way. Blowing on the intake tube suggested a real problem: Neither open or closed position was absolute, although closed allowed pretty much free flow through bypass channel.
I disassembled heater valve to see the monkey works. Design is as follows: Two brass/copper plates slide past one another in a narrow channel. One is supposed to be in fixed position, other slides past to direct coolant flow through core or through bypass channel. Aperature on sliding piece changes with position to allow control over heated coolant that flows through core.
Problem was that inner "fixed" plate was, in fact, mobile. It was designed so that a plastic lug inserted through a drilled hole in the plate engages a recess in the molded valve housing. The recess was either filled with the stub extension of the plastic lug or not a recess at all; I suspect the former, since the residual lug did not extend past plate. The "fixed" plate therefore had full travel of the channel required for travel of valve-controlled plate, and (variable) misalignment of the plates explained why I had heat at first but lost it later.
My solution? I drilled out the remnant of the plastic lug in the "fixed" plate and allowed the drill bit to travel far enough to recess into valve housing. I drove a thin aluminium screw into the plate hole just far enough for threads to gain purchase in the recess, then used the Dremel to cutoff screw head and even the stud surface to that of fixed plate. On replacement of sliding plate I could tell that screw tip was not far enough into housing to allow paired plates to fit snuggly into channel, I used a punch to seat the lug and checked for smooth travel on reassembly of valve.
Guess what? I got heat, baby. Even better, I got heat control-- I can tune cabin temp to whatever comfort level I want (although I am so exceedingly proud of my fix that I have mostly left the temp setting on Broast). That pride will doubtless precede a fall, but for the moment I am happy, my Saab is happy, and I thought I'd share the story with the only folks who could even potentially appreciate it (trust me, I've tried).
Scott
posted by 66.168.1...
, Mon, 15 Nov 2004 22:27:28 <-- Viewing This Message
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