Heater Hose Diagram

AristonSpeedShop

AristonSpeedShop

Well-Known Member
Messages
80
Reaction score
47
Location
Colorado Springs, Colorado
I am having trouble finding good diagram on heater hose routing. Again I am at a loss cause I got car disassembled. Looks like a tube on rear of head and the small tube off of front water manifold feed heater. But there is a small hose fitting, 5/16" on side of block that I can't determine where it goes? Does anyone know the direction of coolant flow? I am not going to use carb heaters as switching out fuel system. Been reading about some installing a heater coolant flow valve as well. Thanks, David
 
The small fitting feeds the Zenith water chokes. Hose from rear manifold goes to upper heater pipe, lower heater pipe goes to back of head.
 
I've been using a solenoid driven Audi/VW shutoff valve. Fits nicely, inexpensive and easy to find used or new. PN 4H0121671D. Hidden switch in glove compartment.

IMG_5087.JPG

IMG_5088.JPG



IMG_5089.JPG
 
bluecoupe30! said:
Interesting Luis, and great photos. I have seen other valves used here, but they have 2 inputs and 2 output attachments. How does this Audi part work? Thanks, Mike
Click to expand...

This valve simply cuts off the flow of coolant that emerges from the back of the head and prevents the hot coolant from flowing into the heater core.

There is the belief by some that interrupting the flow in that manner would somehow overheat the back of the head. I don't believe so.

As the coolant flows from the pump into the block it flows upward into head through many (12?) cavities that surround each cylinder. The outlet in the back of the head diverts some of this heated coolant to the heater core and the intake manifolds to improve cold running. Blocking the flow to the heater and manifolds does nothing to impede the fast and furious flow of the coolant around the cylinders and head.

In fact, the opposite argument can be made that diverting some coolant out the back of the head slightly diminishes the flow through the head. Just as it would happen if you place a 1 to 2 hose divider in your outdoor home faucet and now each hose has to share the pressure of the water supply, leading to slower flow. I don't believe this is a meaningful reduction in flow or even measurable in the case of the engine but I put it out there to help visualize what is going on.

When it's sufficiently cold that I would want some amount of heat in the car I turn on the valve and that helps warm up the manifolds plus provide me the heat I need in the cabin and easily turn it off later as the day and or the engine have warmed up.

But... I am no fluid dynamics engineer, only an amateur, so take all this with a grain of salt.

Interestingly, BMW provided this type of single hose cutoff as an option for AC cars in the E3 and many (all?) later M30 equipped cars.
 
The last production engine M30b35 for five years had a blocking plate at the back of the head - no coolant flow at all.
 
Luis A. said:
This valve simply cuts off the flow of coolant that emerges from the back of the head and prevents the hot coolant from flowing into the heater core.

There is the belief by some that interrupting the flow in that manner would somehow overheat the back of the head. I don't believe so.

As the coolant flows from the pump into the block it flows upward into head through many (12?) cavities that surround each cylinder. The outlet in the back of the head diverts some of this heated coolant to the heater core and the intake manifolds to improve cold running. Blocking the flow to the heater and manifolds does nothing to impede the fast and furious flow of the coolant around the cylinders and head.

In fact, the opposite argument can be made that diverting some coolant out the back of the head slightly diminishes the flow through the head. Just as it would happen if you place a 1 to 2 hose divider in your outdoor home faucet and now each hose has to share the pressure of the water supply, leading to slower flow. I don't believe this is a meaningful reduction in flow or even measurable in the case of the engine but I put it out there to help visualize what is going on.

When it's sufficiently cold that I would want some amount of heat in the car I turn on the valve and that helps warm up the manifolds plus provide me the heat I need in the cabin and easily turn it off later as the day and or the engine have warmed up.

But... I am no fluid dynamics engineer, only an amateur, so take all this with a grain of salt.

Interestingly, BMW provided this type of single hose cutoff as an option for AC cars in the E3 and many (all?) later M30 equipped cars.
Click to expand...
Makes sense and I will likely switch my 4 hose diverter to this at some point. Question, does the electric Audi/VW valve default to the open or closed position, meaning, does the flow shut on or off with 12v power? I'd prefer to have it open (coolant to the heater) with 12v if possible.
 
This makes a lot of sense. Plus there are many simple manually-operated valves available, that will fit in this location and can be opened or closed depending on time of year or outdoor temperatures.
 
Stevehose said:
Makes sense and I will likely switch my 4 hose diverter to this at some point. Question, does the electric Audi/VW valve default to the open or closed position, meaning, does the flow shut on or off with 12v power? I'd prefer to have it open (coolant to the heater) with 12v if possible.
Click to expand...
With no power applied the valve is open. Most electric or vacuum actuated heater control valves I am familiar with default to open when the control voltage or vacuum fails. The Germans seem to do this consistently as a no heat condition can be more devastating than the opposite. Or so they believe...
 
bluecoupe30! said:
This makes a lot of sense. Plus there are many simple manually-operated valves available, that will fit in this location and can be opened or closed depending on time of year or outdoor temperatures.
Click to expand...
I had a manually operated (via cable) "4 Seasons" brand metal valve. Not only was it difficult to route the stiff control wire into the car but even when completely closed it allowed a minute amount of hot coolant to pass. It doesn't require much 200 degree water to heat up that copper/bronze core to an extent that it will be felt inside.
 
I use a heater solenoid switch from an e28. The lower hose from it matches the input to the heater nicely when mounted on the scuttle panel. I use a purple lensed switch (thanks Harry) which matches the rear window defrost etc switches. As the lack of voltage opens the switch, the wiring needs to be adapted to power the switch light when the heater is on.
 
Ian C said:
I use a heater solenoid switch from an e28. The lower hose from it matches the input to the heater nicely when mounted on the scuttle panel. I use a purple lensed switch (thanks Harry) which matches the rear window defrost etc switches. As the lack of voltage opens the switch, the wiring needs to be adapted to power the switch light when the heater is on.
Click to expand...
 
This solenoid heater valve you mean ?
 

Attachments

  • 1B3E63B7-7666-426A-8A51-2E250AB995EB.jpeg
    1B3E63B7-7666-426A-8A51-2E250AB995EB.jpeg
    312.9 KB · Views: 73
That’s the one. The u shaped e28 hose puts the body close to an unused captive nut on the scuttle panel. The hose from the back of the head needs to be extended to reach. I used an emergency flasher switch with a purple lens to control it.
 
I rebuilt mine just before before my e28 dd died. I'd also had a hose inlet on the plastic housing break, so grabbed a few spares from the boneyard while they were still showing up there.
 
You must log in or register to reply here.
Back
Top