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.

img_2730-1024.jpg
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.


img_2726-1024.jpg
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.


img_2727-1024.jpg
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.


img_2728-1024.jpg
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.
img_2731-1024.jpg

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.
img_2732-1024.jpg


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.
img_2735-1024.jpg

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.
img_2736-1024.jpg

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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KHB

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Having seen an '83 533i with a shutoff valve rather than a bypass set up, I decided to go that route since I have Zeniths and with little room to work with. I happen to find at the local pick-n-pull lot a '97 Honda Civic with the engine removed and sitting on the firewall was a cable controlled heater shutoff valve. For $7 I bought it so I could see if it would fit. Its overall length is 3 inches.

Since it's plastic, I decided I wanted the most expensive cheap plastic I could find so I went to the Honda dealer to get a new one in hopes they have more strict controls over their supply base rather than one from a local auto parts store. The Honda P/N is 79710-SR3-A01 and was $56.87. While the OD of the Honda heater hose was the same as the BMW, the ID was a little smaller - maybe 1mm so the hose went on with little resistance. That was the one thing I didn't like. It leaked at first, but tightening the clamp another turn resolved that.

The heater valve is in the open position in the photo (which hopefully is attached).
 

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Stevehose

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Bypass with triple Webers

After much procrastination I installed my bypass valve that has been sitting around for a couple months. I went with the AC Delco 15-5533 valve but removed the vacuum canister and will operate it manually when needed which is only a couple times a year here (but it seems often at the wrong time when wanting to drive).

I have triple Webers so I needed to plumb a little differently than a CSi or Zeniths. Here is my part list:

3/4" heater hose
5/8" heater hose
clamps
3/4 x 3/4 x 1/2 copper tee
3/4 to 1/2 copper reducer fitting
Dayco hose C87624 from Autozone
Dayco hose B87629 from Autozone
A BMW hose that I found in my parts bin with 12665093 written on it, this will go from the back of the head to the reducer fitting. It's the left hose in the pic but any right angle type hose can be fit as long as it is about 7/8" to fit the pipe off the head. It's connected via the reducer to the curved 5/8 hose B87629 because that's what fits going into the valve:
IMG_1345.JPG


Here it is the valve with the other Dayco hose connected and you can see the tee and the reducer:
IMG_1351.JPG


For Webers I use the cooling hoses from an E24 and I replaced the plastic tee (#3) with the copper one but kept the other hoses, the valve connects to the right side of the tee, #4 comes from the reservoir and #1 goes to the thermostat housing:
B0000952.png



And here is everything hooked up, from the firewall I used a 5/8 hose for the small valve fitting on top and a 3/4 hose for the larger valve fitting on the bottom, both fit snuggly on the heater pipes at the firewall. It all fits under the carb trumpets and will largely be hidden when the trumpets are reinstalled:
IMG_1358.JPG


Now that this is installed it probably won't be needed until next year!
 

deQuincey

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it is even beautiful !
very nice, neat, and clean design of the flows using appropriate hoses
i have not solved mine yet :sad:
 

deQuincey

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Having seen an '83 533i with a shutoff valve rather than a bypass set up, I tached).

i would not go that way, when you see that setup, you should consider all the details, i do not think that fitting an '83 solution on a '71 engine without any consideration is a good idea, who knows if the water passages had been redesigned to accomodate the flux needs once a shutoff is considered
 

m5bb

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Good job Steve.

Mine will be similar with the same valve but my Webers are not as high up off the engine like yours with those manifolds so my exits off the heater core have to go straight down. Otherwise about the same.

Later,
Gary
 

Stevehose

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You could probably find 3/4 and 5/8 "S" shaped hoses to drop the valve down a little. I scanned the Napa and Autozone catalogues for hours looking for something that would fit and there are lots of hoses with shapes like that either as-is or that could be trimmed to fit. Fortunately 3/4 and 5/8 are fairly common sizes.

Good job Steve.

Mine will be similar with the same valve but my Webers are not as high up off the engine like yours with those manifolds so my exits off the heater core have to go straight down. Otherwise about the same.

Later,
Gary
 

Luis A.

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Sorry to stir the pot but I am still on this camp. I haven't seen any compelling arguments as to why coolant should be allowed to flow out of that little opening in the back of the head when there are ample return flow paths through the block all throughout the length of the block, including the area around cylinder 6. And on top of it all, the BMW-engineered solution was a shutoff valve on the E3 (not sure why not on the E9...no room?), E12, E23, E24, E28 and I stopped looking at E30, which uses an electrically operated water shutoff valve on the return coolant flow as seen below. That would be a slick solution by having it be activated when the AC blower switch is on.

All that being said, very elegant solution Steve!

i-QSMWDQj-L.jpg




Having seen an '83 533i with a shutoff valve rather than a bypass set up, I decided to go that route since I have Zeniths and with little room to work with. I happen to find at the local pick-n-pull lot a '97 Honda Civic with the engine removed and sitting on the firewall was a cable controlled heater shutoff valve. For $7 I bought it so I could see if it would fit. Its overall length is 3 inches.

Since it's plastic, I decided I wanted the most expensive cheap plastic I could find so I went to the Honda dealer to get a new one in hopes they have more strict controls over their supply base rather than one from a local auto parts store. The Honda P/N is 79710-SR3-A01 and was $56.87. While the OD of the Honda heater hose was the same as the BMW, the ID was a little smaller - maybe 1mm so the hose went on with little resistance. That was the one thing I didn't like. It leaked at first, but tightening the clamp another turn resolved that.

The heater valve is in the open position in the photo (which hopefully is attached).
 

decoupe

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For what it's worth, the B35 cylinder head common to the 3.5 litre e24, e32 and e34 all have block-off covers on the rear so for that cylinder head, a simple open/closed valve should be fine. The late moronic intake manifold (aka the squid) leaves little room for the plumbing required to use a diverter setup.
 

Stevehose

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Solid arguments but I am not taking a chance with my '72 head :-(

Sorry to stir the pot but I am still on this camp. I haven't seen any compelling arguments as to why coolant should be allowed to flow out of that little opening in the back of the head when there are ample return flow paths through the block all throughout the length of the block, including the area around cylinder 6. And on top of it all, the BMW-engineered solution was a shutoff valve on the E3 (not sure why not on the E9...no room?), E12, E23, E24, E28 and I stopped looking at E30, which uses an electrically operated water shutoff valve on the return coolant flow as seen below. That would be a slick solution by having it be activated when the AC blower switch is on.

All that being said, very elegant solution Steve!
 

afeustel

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This is what I ended up with for the Bavaria. Control is a via a vacuum solenoid mounted on the ground tab on the firewall.
 

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Peter Coomaraswamy

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Rob, with your family's permission we could burry you right next to Bill Lear (inventor of the 8-track)... He got it right with the jets though and I'm sure you have your successes :)

And Drew, we know you got that from the parts bin at NASA :)
 

afeustel

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There is a small solenoid that controls a vacuum pass switch mounted to the fire wall. That solenoid switch is activated by a 12 V signal from a small round black rocker switch (which is pretty slick and low profile that I probably bought at Autozone) mounted under the steering column right next to the rear defrost switch. So basically I hit the switch and it allows vacuum signal to pass to the heater bypass vacuum which rotates the bypass arm. Other option is to have that electrical signal keyed to when the A/C compressor turns on but that would just allow heat to build up in-between compressor cycles so I choose to activate manually (I just have to remember to do it when I want to run the A/C).
 

thehackmechanic

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Jay, thanks!

Drew, I tried exactly what you have with the vacuum actuator to the valve, but found that that only allowed all-on or all-off positions of the valve. I found that, in the fall, I liked having the valve cracked slightly open. That's why I went with the electronically-controlled servo-actuated valve on page 5 of this thread. It's not a question of wrong or right; I'm just reminding myself why I did it, and letting others see the pro and con.
 

afeustel

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all-on or all-off is good in Houston. I suppose the advantage of the electrical servo is that you reduce the number of components, and also avoid a possible source of a vacuum leak.
 

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Bypass with dual webers

This thread is a bit old but I figured I'd shout out my appreciation for all the information in it, as well as yet another configuration. Standing on the shoulders of giants such as the Hack Mechanic, I was able to fit the Old Air Products electrically controlled valve to my car.

I am firm believer in the need for coolant flow from the head to the intake, and getting that heat out of the cabin really makes the AC much more efficient.

Previous posts have provided solutions for injected, dual Zenith, and triple Weber configurations. While very jealous of not only the accurate fuel metering but also the ample room provided by FI intake runners, I needed to find a place for that valve to fit on my carbed car. I didn't find a clear path from the heater core under the rear carb to the space between the carbs so I concentrated on getting it in between the rear carb and the firewall. There isn't much extra space back there, and the hoses run all fairly close to each other but I was able to figure out a way to get it all tucked in and below the air cleaner.

In order to make all the 90 and U bends, I used most of the hoses mentioned in previous posts, as well as the original hose from the head to the heater core. I started by cutting a section out of that hose so that the valve was inserted in the middle. That determined the basic location for the valve. A simple 90 degree bend was needed for the second heater core connection. That left just the connection from the output of the valve to the intake manifold. Unfortunately, the two nipples were not pointed towards each other so a fair number of bends were required. This was not helped by the difference in size between the large port on the intake and the 5/8" port on the valve.

Before continuing, let me point out that someone at Old Air Products must've been reading this thread because they addressed two of the issues the Hack Mechanic originally encountered -- the small 5/8" ports on the valve and the large molex connector. They now thoughtfully provide thin silicone rubber sleeves that adapt a 5/8" port to a 3/4" hose. Very handy and better than just cranking down on a clamp. They also switched from the large flat 1x5 molex to a smaller 2x3 connector that fishes through the firewall much easier.

Back to that final hose... I found a large elbow from some previous project in a box and was able to use a reducer to adapt that to the Gates 90 degree 3/4" hose and connected that via a straight nipple to to the u-bend Dayco (I think) hose mentioned in a previous post. A bit tortured and a few more connections than I'd like but overall a cleanish install. especially with the factory air cleaner installed.

Thanks again for all the up front research.

Pictures available at: https://goo.gl/photos/Cd4VrN9QTsKmdPCu5 show hoses on the valve, the 5/8 to 3/4 adapter sleeve, the other pieces required to get to the intake, and the smaller molex. I forgot to shoot a pic of the reducer or final assy of that last hose (I didn't install by inserting one hose into the other).
 

deQuincey

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Pictures available at: https://goo.gl/photos/Cd4VrN9QTsKmdPCu5 show hoses on the valve, the 5/8 to 3/4 adapter sleeve, the other pieces required to get to the intake, and the smaller molex. I forgot to shoot a pic of the reducer or final assy of that last hose (I didn't install by inserting one hose into the other).

thanks for posting,
good solution for those non stock carbs, unfortunately stock zeniths have the automatick choke element just there, making interference with the valve, a pity
 
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