Comparison DMCH and Specialt hot water valves

[DrJeff]

I had the opportunity today to do a side-by-side comparison of the DMCH and SpecialtAuto hot water valves. Another owner had suffered a failure on his Specialt valve and advised that I get the DMCH one. Neither of the valves shown have been fitted into a car, so they are just as they came from the vendor.

DMCH (left) and Specialt (right)
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Here I compare the wall thickness (at the failure point). I made sure to measure away from the bulge to get the true thickness. The Specialt valve on the right has been dissected at the time the photo was taken (more on that in a moment). The wall thickness is the same in both cases (2mm).
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This photo shows the Specialt valve as it comes installed in the hose kit. You can just see some foam like adhesive between the top of the hose and where it attaches to the valve (just where the arrow is conveniently pointing).
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Once I pulled the hose off you can see the extent of the 'adhesive like stuff'. Since I wasn't going to use the Specialt valve and I was curious about the adhesive, I decided to see what lay within! I scrapped away the adhesive foam - which was actually very soft and could be removed with just my thumb nail. There was no evidence that the glue was there for any reason that I could see. I cut into the valve stem to see if the stem and the valve body had been glued together. However, as far as I could tell the stem and the body were cast from the same plastic. So it begs the question... why? Was the adhesive an attempt to strengthen the valve at a known failure point?
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I was surprised how soft the plastic was at the base of the stem, of course I don't have anything to compare it with.

[ALEXAKOS]

Kudos for the review!!!!8)
I have heard some complains about DMCH pars..bur I rarely head good things about Special's repro's...

[Bitsyncmaster]

I've seen many warnings when using plastic parts to use no sealers or glue because it can attack the plastic.

[DCUK Martin]

Look familiar? (http://www.ebay.com/itm/NEW-FORD-VACUUM-ACTUATED-HEATER-VALVE-18495-VACUUM-OPENS-5-8-HOSE-/310757769389)

http://i23.ebayimg.com/03/i/001/34/22/556a_12.JPG

[djdogbone]

I'd be willing to bet that the source of failure IS the adhesitve as it is probably weakening the plastic over time.

[Bitsyncmaster]

I just installed a sump pump under my house. It said in the instructions not to use any sealer on the plastic threaded fitting (1 1/4" pipe) because it can damage the plastic. It's made of that same black plastic I see on the heater shutoff.

[NightFlyer]

Personally, I wouldn't use either valve as a replacement, unless you insist on such for concours purposes.

The stock/OEM, DMCH, Hervey cross reference, and Cadillac cross reference are all butterfly valves consisting of a separate vacuum chamber and valve body connected by a mechanical linkage. While there's nothing wrong with this design per se, the pivot shaft for the butterfly valve runs directly through the valve body, thus creating a point of common leakage when the internal seals eventually wear out (my stock/OEM valve was recently leaking coolant from the pivot shaft prior to replacement). Also, the mechanical linkage can easily corrode/rust, get stuck, or even get hung up on other lines/hoses within the vicinity of the valve (it's quite busy back there).

That's why the DMCToday.com crowd prefers to use the AutoZone Everco (by 4 Seasons) #74612. It is a one piece self-contained vacuum actuated piston valve in a thermoplastic housing. No metal to corrode/rust, no mechanical linkage to fail or get hung up, no internal seals to fail, no pivot shaft to leak, and a much smaller footprint in an already crowded area of our engine bays. Not to mention that the AutoZone valve is only $10 and is usually in-stock for immediate pick-up at all AutoZone locations. Not a single reported failure of this valve by any of the satisfied owners running them, including myself.

http://www.autozone.com/autozone/parts/_/N-5yc1s?itemIdentifier=142760

http://contentinfo.autozone.com/znetcs/product-info/en/US/f11/74612/image/3/

[DMCMW Dave]

The stock/OEM, DMCH, Hervey cross reference, and Cadillac cross reference are all butterfly valves consisting of a separate vacuum chamber and valve body connected by a mechanical linkage.]

I have a problem with that design shown. Failure rate is not my issue, I'm sure it will last as long or longer than any of them. My problem is the failure mode. This valve (or any valve) can fail in several ways:

--crack or rust and leak
--get stuck open or closed (I've seen both)
--failure of the vacuum diaphragm.

It's the third mode that would worry me. (The other two faults could happen to any design to the same effects). In the event of diaphragm failures, the older designs with the external linkage simply quit closing the valve and will cause a small vacuum leak in "max" mode.

In this design, failure of the diaphragm (or other internal seal) will cause coolant to be pulled into the engine via the mode switch by vacuum (and force by coolant pressure. (If the mode switch was closed it would probably dump hot coolant inside the console). This would cause some very strange and extremely hard to identify problems, i.e. it would look an awful lot like a blown head gasket.

I can't say I've seen that happen, but sometimes thinking about the "what if" cases is important.

[Bitsyncmaster]

In this design, failure of the diaphragm (or other internal seal) will cause coolant to be pulled into the engine via the mode switch by vacuum (and force by coolant pressure. (If the mode switch was closed it would probably dump hot coolant inside the console). This would cause some very strange and extremely hard to identify problems, i.e. it would look an awful lot like a blown head gasket.

I can't say I've seen that happen, but sometimes thinking about the "what if" cases is important.

Never thought of that failure but it looks like it could happen. A peice of clear hose could show that failure.

[DMCMW Dave]

Never thought of that failure but it looks like it could happen. A peice of clear hose could show that failure.

So would coolant in your console - or exhaust.

[NightFlyer]

That's a GREAT point Dave S, and something that I never thought about either. As one really wouldn't use the heater at all during the hot summer months, perhaps a manual shutoff would be best, and just plug the vacuum line. Something like this - single piece, solid brass, made in USA. For $10, I'm ordering one and will swap out with the Everco when I change the coolant hoses, as that way I can make a little bracket mount for the bulkhead/firewall for the valve to rest in and allow easy access to the wing nut handle.

http://i.ebayimg.com/t/NOS-5-8ths-Heater-Shut-Off-Valve-/00/s/MTIwMFgxNjAw/z/hZMAAMXQaZxSG-db/$T2eC16J,!w4FI,KdNWZuBSG-d,5IqQ~~60_57.JPG

[Bitsyncmaster]

That's a GREAT point Dave S, and something that I never thought about either. As one really wouldn't use the heater at all during the hot summer months, perhaps a manual shutoff would be best, and just plug the vacuum line. Something like this - single piece, solid brass, made in USA. For $10, I'm ordering one and will swap out with the Everco when I change the coolant hoses, as that way I can make a little bracket mount for the bulkhead/firewall for the valve to rest in and allow easy access to the wing nut handle.

http://i.ebayimg.com/t/NOS-5-8ths-Heater-Shut-Off-Valve-/00/s/MTIwMFgxNjAw/z/hZMAAMXQaZxSG-db/$T2eC16J,!w4FI,KdNWZuBSG-d,5IqQ~~60_57.JPG

Put a motor on it:tongue_stick:

Just kiding. That looks like a well made part.

[NightFlyer]

Put a motor on it:tongue_stick:

Just kiding. That looks like a well made part.

I love your project on this part of our cars and am interested in seeing the end results :thumbup2: A little too fancy for me though :)

I'd prefer to do a ball valve, but I can't find anything made with a solid single piece body, thus this was the next best option. I plan on leaving the vacuum line present in case I ever want to go back to a vacuum actuated solution.

[DMCMW Dave]

The failure rate on that NOS water valve is actually pretty low. We've seen one stuck closed, one that leaked at the valve shaft, and a couple where the metal was so rusty that it leaked at that fitting.

On my own car I put a small medical (like you see in hospital vacuum lines) valve on the outlet of the mode switch. The valve is just forward of the console on the driver side suspended by the hoses. I configured it so that the vacuum is either routed normally or sends vacuum to the water valve all the time, so that in the summer I never had hot water in the core to compete with the A/C. Unfortunately my source for leftover medical valves has dried up.

[NightFlyer]

The failure rate on that NOS water valve is actually pretty low. We've seen one stuck closed, one that leaked at the valve shaft, and a couple where the metal was so rusty that it leaked at that fitting.

On my own car I put a small medical (like you see in hospital vacuum lines) valve on the outlet of the mode switch. The valve is just forward of the console on the driver side suspended by the hoses. I configured it so that the vacuum is either routed normally or sends vacuum to the water valve all the time, so that in the summer I never had hot water in the core to compete with the A/C. Unfortunately my source for leftover medical valves has dried up.

Unfortunately, my stock/OEM unit was leaking at the valve shaft, otherwise, I probably would have left well enough alone. I'm wondering if my failure had anything to do with the fact that it was constantly being pulled closed by vacuum from the line, resultant from what I believe to be is a defective mode switch diaphragm. I honestly have no idea how long that problem persisted. I actually just ordered the rebuild kit from Julee not more than 20 minutes ago (together with some other common and one not-so-common parts), so I hope that this is the source of my problem. You can see my post specifying the details of the issues I was experiencing over on Today:

http://www.dmctoday.com/showthread.php?399-HVAC-Problem-Suspect-Mode-Switch

Your solution with medical valves sounds similar in principle to the ends looking to be achieved with Dave M.'s electrical project, albeit with a slightly different approach. Dave M's project can be found here:

http://www.dmctoday.com/showthread.php?283-Electric-controlled-heater-shut-off

[Bitsyncmaster]

That's a GREAT point Dave S, and something that I never thought about either. As one really wouldn't use the heater at all during the hot summer months, perhaps a manual shutoff would be best, and just plug the vacuum line. Something like this - single piece, solid brass, made in USA. For $10, I'm ordering one and will swap out with the Everco when I change the coolant hoses, as that way I can make a little bracket mount for the bulkhead/firewall for the valve to rest in and allow easy access to the wing nut handle.

http://i.ebayimg.com/t/NOS-5-8ths-Heater-Shut-Off-Valve-/00/s/MTIwMFgxNjAw/z/hZMAAMXQaZxSG-db/$T2eC16J,!w4FI,KdNWZuBSG-d,5IqQ~~60_57.JPG

That valve is small enough to install near the heater core. You could probably mount it to open or close via the wheel well or a small hole in your trunk.

[NightFlyer]

That valve is small enough to install near the heater core. You could probably mount it to open or close via the wheel well or a small hole in your trunk.

That's what I was thinking too :biggrin:

I recently ordered a manually retractable radio antenna from DMCH (via DMCMW). If I decide to install the manually retractable fender mount antenna (in place of the fixed mast that came on my car courtesy of the Troy, MI QAC), I'll be having to do quite a bit of work in that general area and am sure that I could come up with something creative here. However I decide to do this, it will either be completely hidden or look factory stock/OEM. Won't be as cool as your electronic set-up though :approve: