DIY - Heater Bypass Valve

While I'm waiting for my new triple core Mark Preisendorf radiator to arrive, I thought I'd deal with some other cooling system odds and ends.

Most of us E9 owners are aware that our cars do not have a conventional heater contol valve that shuts off the flow of coolant through the heater core. Instead, the core is always plumbed, and the heater lever merely opens and closes the flaps on the heater housing. In hot weather, many of us can feel the heat coming off the heater housing. The a/c systems in these cars, never great to begin with, can certainly do without this extra heat load right next to the a/c evaporator.

There have been threads (http://www.e9coupe.com/forum/showthread.php?t=8581&highlight=heater+valve) discussing what is necessary to bypass the heater core. The quick and dirty way is to simply disconnect the two heater hoses from the heater core pipes that protrude through the firewall and splice them together. For those living in hot climates, this is fine, but here in New England, on those spring drives, I USE my heat. A second approach is to install a valve, like in a 2002, that simply stops the flow of antifreeze into the core. However, there is concern that this approach, which does not allowing the coolant to circulate, may cause overheating problems. Clearly what is needed is a full heater bypass valve that, when opened, sends coolant through the core and, when closed, bypasses the core without blocking the flow.

For reference, the hoses into the firewall are shown below (hose clamps removed). The top hose goes to the back of the head. The bottom hose (on my L-Jet M30B32) feeds the metal pipe that runs under the intake manifold.

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IMG_2730-1024.jpg


It is easy to imagine the valve that we need. It is shaped like a letter H. The top legs of the H are connected to the heater pipes at the firewall, and the hoses go into the bottom legs of the H. When the valve is open, it should block off the center section but allow coolant through the legs to and from the heater core, and when the valve is closed, it should bypass the core by diverting the coolant coming up the left leg, through the center section, and out the right leg. But how do you locate one the right size, and what adaptations to you need to do to make it work in the E9?

In a perfect world, we'd find a bypass valve that:
--Has 3/4" pipes (this is the size of the heater pipes protruding through the firewall)
--Has a 1.5" center-to-center (2" edge-to-edge) spacing between the pipes (this is the spacing of the heater pipes protruding through the firewall)
--Is metal

In practice... one out of three ain't bad, and close is good enough for horseshoes and hand grenades.

To locate a usable valve, I went on eBay, typed in "heater control valve," and spent an hour looking at lots of pictures, eventually finding three that are widely available through both the AC Delco and the Four Seasons cataloges. They're all cheap (less than $35). Because it's impossible to tell what will work and what won't until you actualy test-fit them, I simply bought all three. I think the total bill was about $60.


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IMG_2726-1024.jpg


Note that all three of these have a lever on the end of the valve, which is, in turn, actuated via a vacuum dashpot. So in order to change from the heat to the no-heat setting, you could either remove the vacuum dashpot and simply move the lever (or wire it in position), or leave the dashpot installed and connect and disconnect it from the intake manifold to flip between enabled and bypassed.

Note also that, to connect any of these three candidate bypass valves to the two heater hoses, the heater hoses need to be either trimmed or lengthened.


AC Delco 15-5533
Verdict: This should work.
Advantages: The pipes are almost exactly the same spacing as the heater pipes, allowing clean attachment to the pipes on the firewall.
Disadvantages: The pipes are 5/8", not 3/4". And it's plastic.


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IMG_2727-1024.jpg


The first one is AC Delco 15-5533 (Four Seasons 74781). This is not a classic "H" shape, but it has two inlets and two outlets. The one I bought came without the vacuum actuator, so the lever controlling the valve is plainly visible and completely exposed. In this picture, the flow of coolant in is supposed to be from the top right. The tube size is only 5/8" instead of the correct 3/4", but you can snug the hoses down with hose clamps. And, the spacing of the two tubes on the left is about 1.5" center-to-center -- almost exactly the spacing of the two heater pipes on the firewall. Unfortunately, the part is plastic -- an anathema to those of us who pride that our E9s don't have the plastic junk endemic in the cooling systems of newer BMWs.

The pic below is a test fit of this valve using two short 3/4" rubber hose sections to hold it onto the firewall. In order to have clearance for the lever, the lever must go on the left (away from the intake manifold). This forces you to install the valve upside down from the previous photograph, so the inlet side is lower left, where you can just barely see it. The outlet side is plainly visible upper left. The hose going to the metal pipe under the intake manifold is swung to the side. The hose coming from the back of the head is not visible.

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IMG_2733-1024.jpg


In the photo below, I've swung the outlet hose back toward the valve so you can see that the natural elbow in this hose will allow the excess to simply be cut and the hose connected (I have not yet cut it; this is a test fitting). The hose from the back of the head will need to be lengthened with a 3/4" barb coupling and brought into the inlet at lower left (not visible).

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IMG_2734-1024.jpg


So you can see that this should work. If you look up this part number on line, you'll see the vacuum actuator bolts on top of the lever, so it would be on the left. It looks like there's sufficient room for it.


AC Delco 15-5543
Verdict: This should work.
Advantages: The pipes are 3/4". And it comes with hoses on it, allowing quick attachment to the heater pipes on the firewall.
Disadvantages: The pipes are slightly too far apart. And it's plastic.


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IMG_2728-1024.jpg


The next one I tried is the AC Delco 15-5543 (Four Seasons 47607). This looks to be exactly what you need, although, like the 5533, it is plastic. The pipes are 3/4" -- the right size. It's H-shaped with the actuator on the top. It even comes with two 4" sections of 3/4" hose on the ends, allowing quick attachment to the heater pipes. The inlet end isn't labeled, but I assume it's the one opposite the valve, or upper left, In this first pic below, I do a quick test fit. The 4" rubber hoses are longer than they need to be, so it sticks out a bit far.
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IMG_2731-1024.jpg


Below I've trimmed the 4" hoses down to about 2". Unfortunately the pipes on this valve are slightly further apart than those on the firewall, and the shorter you cut these hoses, the more difficult a time they have mating up securely to both sides. Also in this pic, I swing the hose from the intake, showing that, like with the 5533, it looks like this hose can simply be cut just after it makes its elbow turn and then clamped directly to the pipe. Also, as with the 5533, the inlet hose from the back of the head (not pictured) need to be lengthened in order to be connected to the valve. The vacuum actuator can be taken off and the lever flipped manually, or if you like, the actuator can be used to close the valve; just hook a vacuum line to the intake manifold.
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IMG_2732-1024.jpg


AC Delco 15-5302
Verdict: I have my doubts.
Advantages: It's metal.
Disadvantages: The pipes are slightly too far apart. One pipe is 3/4", the other is 5/8". There may be clearance issues.


img_2729-1024.jpg
IMG_2729-1024.jpg


I looked long and hard for an H-shaped metal valve, and this was the only one I could find. Initially I thought it was The Grail, but the vacuum actuator is on the side, and valve, pipes, and the vacuum actuator sit at an angle with respect to each other. Further, what is marked as the inlet tube is 5/8" whereas the outlet tube is 3/4". Also, the outlet and inlet tubes extend unequal distances. Individually none of these are showstoppers, but they make a clean installation challenging. In the pic below I have the valve cajoled into hanging there on the firewall. You can see that the tubes are slightly too far apart to mate cleanly with the firewall tubes, though slightly longer stub hoses would solve this problem. In this position, this could work, but technically the flow arrow is pointing the wrong way.
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IMG_2735-1024.jpg


In the pic below, we turn the valve around so the flow arrow is pointing toward the heater, and you can see that there's a clearance problem, with the body of the valve hitting the #6 intake plenum.
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IMG_2736-1024.jpg


So, it looks like either of the two plastic bypass valves -- the 5533 and the 5543 -- will work. As much as I dislike putting plastic in the cooling system, unless I can find a better metal bypass valve, I'll likely go with one of these. Plus, the color and the look and feel of the metal valve, to me, are somewhat at odds with the rest of the rest of the engine compartment. Of the three, interestingly, the 5533 seems to be the least visually intrusive. The 5543 is a quicker and easier adaptation, but that vacuum dashpot is sitting pretty high and looks fairly un-BMW-like (of course you could take it off). On the 5533, the dashpot unscrews, but on the 5543, it is a more integral part of the assembly, not as easily removed.

To finish up the adaptation and extend the inlet hose from the back of the head, I've ordered a length of Gates 5/8" heater hose (28491, $10.03 at Amazon) and Gates 3/4" heater hose (28492, $9.64 at Amazon), and several brass right angle 5/8" and 3/4" fittings (eBay; PEX fittings look like they'll work).

I'll amend the post when the final installation is done.

--Rob
 
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Stevehose

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Great post - it would be cool if it could be rigged it in a way so that when you slide the heat bar to red it would activate the vacuum dashpot via a solenoid of some sort. Right now I am full bypass but would like the option to have heat without the mess of removing the elbow and bleeding the system each time.

What about these?

http://www.watts.com/pages/_products_sub.asp?catId=64&parCat=2238

Or solder a short piece of copper pipe into each opening and attach the hoses:

http://www.ebay.com/itm/NEW-FLECK-S...174?pt=LH_DefaultDomain_0&hash=item2eb2c7ad9e
 
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thehackmechanic

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<<It would be cool if it could be rigged it in a way so that when you slide the heat bar to red it would activate the vacuum dashpot via a solenoid of some sort.>>

Yes, that's the extra-credit-apple-for-the-teacher step.

<<What about these?>>

I briefly looked on McMaster-Carr and didn't find anything directly applicable because they all had three ports. These do have four ports, but unless the pipe spacings are 1.5" on one side (and it doesn't look like they are), it looks like they're not as good a fit as the automotive valves.
 

thehackmechanic

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Heater Control Valve Installation: Part II

It's taken much longer than I thought, but I've completed (well, nearly) the heater bypass valve installation.

If you've read my Roundel columns, you know that I'm not the "do it once, do it right" type. That very phrase, in fact, drives me nuts, because it's a value judgement solemnly intoned by someone who isn't spending YOUR money. That having been said, I was surprisingly sensitive to what looked out of place in my dear E9 that I've owned for 25 years.

In the previous installment, I looked at three heater control valves. I settled on the AC Delco 15-5533, since the pipe spacing is nearly identical to that of the pipes coming through the firewall, allowing you to run very short stub hoses. The pipe size, though, is 5/8" instead of the 3/4" size of the hoses, but the hose clamps seem to squeeze down ok on the hoses.

I could've had it together in an evening by simply splicing sections of hoses with right-angle connectors (the heater inlet hose that runs from the back of the head has to take a few tight turns). I tried, several times, to splice it. It didn't look right. I tried to tuck the splices down in crevaces so I wouldn't see them. It still didn't look right. I never would've predicted that my eyeballs would've been so sensitive to this.

So I looked for a solution that would allow me to run a single hose, without any splices, from the back of the head to the inlet of the valve. I tried several, but in the end found a Gates 28476 3/4" heater hose that's 22" long, with a 18" long straight section, followed by a right angle bend, followed by a 4" straight section.

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IMG_2752-1024.jpg


I cut about 6 1/2" off the long section and 2" off the short section. This was done by trial-and-error and test-fitting the hose each time. The short pipe at the back of the head is a bear to reach, but I got good at snaking my arm back there and pushing the hose onto it. A few drops of glycerin smeared inside the hose helped things considerably. When I had to tighten it up for good, I thanked the Automotive Powers That Be for my flexible hose clamp driver (my new favorite tool in the entire world).
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I attached the long section to the back of the head, and ran it beneath the intake manifold and above the starter motor. The pic below is before I'd fully trimmed the hose. Note that the second hose -- from the pipe under the intake manifold -- was trimmed for length, and is folded back for clarity.

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IMG_2754-1024.jpg


The pic below shows the heater control valve, with its stub hoses, installed against the firewall, with the hose from the back of the head attached. The second hose is still pulled back for clarity.

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IMG_2756-1024.jpg


Below is everything attached.

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Below is a pulled-back photo showing that the installation is actually fairly unobtrusive and doesn't cry out "some Hack Mechanic retrofitted an A/C Delco heater control valve."

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IMG_2760-1024.jpg


Note, as per the previous installment, I've elected to use the valve without the dashpot, so I'll manually throw the lever when I want to enable or disable the heater core. I'll have to see if, over time, it stays in position or if I need to secure it in some fashion. The same valve is available with the dashpot, in which case it could be hooked to the intake manifold with a relay-controlled bypass, to enable or disable it. I wasn't interested in making it any more complicated than it needed to be.

Note also that this is all easily removable, and, if need be (if for example the valve fails on the road), the two hoses that feed the bypass valve can still be hooked together, as people do with the brute-force bypass.

I'll post again when the system is filled with coolant and tested, but this looks promising. It'll be interesting to see if the a/c works demonstrably better without the little radiator sitting right next to it.
 

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jmackro

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I'm not the "do it once, do it right" type. That very phrase, in fact, drives me nuts.....

That expression is pertinent to simply unbolting one factory part and replacing it with another factory part. But when you are engineering something new, you aren't going to get it right on the first try. So, "do it once, do it right" might be an OK expression for a task requiring no creativity, but when you're doing R&D, some iteration is always needed.

Thanks for sharing your research on solving the "heater always on" problem!
 

x_atlas0

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Why not grab the part from a later BMW, like an E34 540? It's got these two huge solenoids which open or close the flow to the core, just like you want. The wiring would be cake with just a switch. You would have to make a bypass hose for the aux pump connection, but other than that, it sounds like it would do what you want.
 

thehackmechanic

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Why not the E34 method?

If someone else does it this way, I'd love to see the result. I gave it a quick look-see and opted out for several reasons. Firstly, there were posts on this and other forums that said that simply blocking the flow (like is done with the heater control valve on a 2002) would be bad for the cooling of the rear cylinders of the engine, and because the heater control setup of an E34 has three hose fittings not four, I couldn't convince myself that it bypasses in the way that I wanted (of course you could also argue that, however it -- or the bypass setup of an E24 -- worked, it meant that that technique was unlikely to overheat the engine or they wouldn't have used it).

Also, that E34 valve ain't small. I wanted something that didn't eat up a lot of space and didn't dominate the look of the engine compartment.

Lastly, I wanted to keep it as simple as possible. This is a lever that'll probably be flipped once a season.
 

JMinNJ

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Rob,

Nice work. It's the hackmechanic column with pictures. It doesn't get better.
 

Nicad

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That is a good idea with the choke cable. How much does the heater core contribute to cooling the engine? I suppose it is only when the fan is on?
 

thehackmechanic

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How much does the heater core contribute to cooling the engine?

Well, I'll find out :^) Got it back on the road today.

And the choke cable's a great idea.
 

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David

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Great post.

I don't know about the rest of you, but I can feel the heat pouring into the cabin. I've run heat proofing material from Dynamat all the way up the firewall, but I don't think it did much. I'm curious to hear if this works. Here in LA, a heater is rarely needed.

-D
 

Stevehose

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I did the bypass mod a year ago (thanks Jerry) and it definitively makes a big difference - no heat soak into the cabin.
 

jmackro

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How about adding a choke cable under the left dash compartment so you can actuate the valve from inside the car?

I suppose if you were someone who found disassembiling e9 dashes fun, you could modify the function of the lever on the dash to switch the coolant valve. The factory uses that lever to move the door in the heater box which regulates the flow of always hot air. That door could be permanently set to the "open" position (or perhaps removed altogether) if the flow of hot water to the heater core could be regulated. Then a longer cable could be run from the lever, and used to control the new water valve.

This is the way that virtually every other car regulates heater temperature.

But am I going to pull apart my e9's dash & heater box to make this mod? Nah!
 

John S

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You'll want to make sure that you open up the valve once in a while so that you don't have stale coolant in the heater radiator all the time. If you don't flush out that stale coolant, your radiator will corrode much more quickly. The same thing happens with the heater cores on the 2002 when the owner fails to open up the valve for a long period of time.

John
 

deQuincey

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You'll want to make sure that you open up the valve once in a while so that you don't have stale coolant in the heater radiator all the time. If you don't flush out that stale coolant, your radiator will corrode much more quickly. The same thing happens with the heater cores on the 2002 when the owner fails to open up the valve for a long period of time.

John

good point !
 

David

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I was going to start this job today, but Im not sure I have the correct bypass valve. The part number you show seems to have the same size OD on the inlet and outlet. However the Delco 5333 I purchased has different sized inlet and outlet pipe OD. Here is a shot of what the 5533 I purchased looks like:

http://shopping.yahoo.com/754067935-acdelco-heater-water-shutoff-valve-15-5533/

Looks a bit different than yours. Are you certain that the part is Delco 5533 ?
 

deQuincey

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yes you can see that the additional lateral cylinder was removed for manual operation
 
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