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djkeev
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 Posted: Mon Dec 14, 2020 11:00 am Post subject: WBX 2.1 Coolant Circulation |
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I posted this in another thread but think it is worth its own thread.
I searched for answers on how the Bleeder Loop on the 2.1 actually works but every post or article I find on the WBX 2.1 cooling systems ignore this self bleed system. At best they say something like "The 2.1 has an improved air bleed design" but never say exactly how it works.
The following is what I've come up with based upon a half Century experience of twisting wrenches, first hand 2.1 experience and by simply studying various drawings.
| djkeev wrote: |
NOTE: to avoid mis-information and confusion I will edit this initial post as I learn new and most importantly, correct information.
*****************
Ok,
I will admit that I do NOT fully understand the bleeder ring on the 2.1 cooling system.
But..... here are my thoughts on how it works.
Let's start in the RF of the engine.....
1) There is a hose from the upper portion of the coolant distribution tower port to the bleeder ring. If memory serves..... 5/16” hose. (8mm? )
2) a hose comes from the lower thermostat housing, again 5/16”
3) a hose cones from the upper thermostat housing, again 5/16”
4) a hose comes from the left head, once more 5/16”
6) yep, we skipped #5 a hose comes from the right head, another 5/16”
5) a larger pipe nipple, about 3/8” ? Joins to a hose that enlarges to 5/8” and connects to the upper nipple on the expansion tank.
Now, the lower expansion tank nipple connects to the metal coolant pipe running from the thermostat housing to the water pump.
From this drawing of the coolant flow (thanks Bensplace) the coolant is flowing from the thermostat housing and the heater return hose to the water pump. Labeled as "bypass tube metal" ....... left side of drawing.
***************
NOTE: THIS DIAGRAM BELOW IS INCORRECT!
SCROLL DOWN TO FIND NEW CORRECT DIAGRAMS (2) ONE FOR COLD (thermostat closed) and ONE FOR HOT (thermostat open)
***************
One must ask, is the coolant being sucked or pushed along as it returns to the water pump?
The water pump is pushing coolant into both heads.
If the thermostat is closed, the coolant from both heads is immediately returned to the water pump (except for any heater draw off) via the metal pipe from the thermostat to the water pump.
So, sucked or pushed, there is a flow TO the water pump.
I vote for it being sucked in that pipe.
Now, if you look at this GoWesty parts drawing, all of the hoses connecting into the bleeder ring are active in the cold loop except for the upoer thermostat cover bleed. EDIT: (12/14/20 ) This upper thermostat bleed is Only active when the valve is opened to bleed air from the upper housing as the system is initially filled with coolant.
Note that coolant is being pushed into the coolant distributor immediately after the Right head. There is a hose from the top of the coolant distributor to the bleeder ring. This coolant distributor connection is the beginning of the bleeder ring circulation loop.
Cold coolant is pushed via the path of least resistance from the coolant distributer to the lower thermostat housing which begins to warm the thermostat.
There is a bleeder hose from the lower thermostat housing. Coolant is pushed into the bleeder ring joining the coolant distributer bleeder ring flow.
Both heads have small bleeder ports that connect to the bleeder ring. I believe this port on both heads pushes coolant into the bleeder ring.
After the thermostat housing where the coolant from both heads is pushed in to, the coolant now exits to be returned to the water pump...... I will say it is being sucked to the water pump.
I think it being sucked is important because this sucking action sets up the coolant flow through the Expansion Tank.
I see the expansion tank flow as being top to bottom..... I always thought it was flowing up from the bottom!
The coolant is being drawn into the expansion tank via the small upper nipple and sucked out the large lower nipple because this lower nipple is connected to the metal suction pipe from the thermostat housing to the water pump.
Any air in the coolant will get trapped in the expansion tank in the "dead" space above the small upper intake nipple.
As the coolant warms and expands, this trapped air is forced out of the expansion tank and into the recovery tank behind the license plate. The air comes out along with any excess coolant being pushed out by hot liquid expansion.
Why the small sized "IN" nipple and the large exit nipple?
I can only guess that it regulates the coolant flow enough giving the air in the coolant a chance to rise out of the coolant as it "slowly" passes through the expansion tank.
I also think this is why the bleeder ring is only about a 1/4” inner diameter. To slow the flow and capture any air in the coolant as it passes through each cooling component. Air rises given the opportunity. But if air is trapped in liquid, it will get pushed along with the liquid.
As the system warms and the thermostat opens, the coolant flow is diverted through the radiator and EDIT: (12/14/20 ) the hose that was feeding the Right head coolant from the coolant distributor to the lower thermostat housing actually reverses flow direction when the thermostat opens. Now this hose routes Left head coolant into the coolant distributor, mixes with the Right head coolant and proceeds to the Radiator.
All this to say, that I believe the 1/4” NPT upper fitting on this tank is very adequate.
The air capturing aspect of the expansion tank is served just fine through the small bung size.
The expansion tank has Little to do with actual cooling (except that liquid under pressure has a HIGHER boiling point than water at atmospheric pressure has, by maintaining a steady system pressure, it does help regulate coolant temperature) It only handles trapped air removal and the regulation of expanding/contracting liquids pressure.
I hope this wordy post makes sense?
Dave |
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Last edited by djkeev on Thu Dec 17, 2020 6:06 am; edited 2 times in total |
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crazyvwvanman
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| Posted: Mon Dec 14, 2020 12:21 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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Thanks for doing this as more understanding is helpful.
I think you covered the bleeder loop pretty well and yes coolant flow in the tank is from top to bottom.
The reason the lower output hose of the main tank needs to be much larger than the bleeder loop feeding into the tank is for when the cap is off and you are filling the system.
The constant bleeder loop coolant flow bypasses the radiator so is keep intentionally small to allow most flow to go through the radiator.
You are off a little on the small bleeder hose at the top of the thermostat cover. That has a manual valve that is intended to be opened only during cold filling and bleeding.
This lets trapped air escape as the waterpump fills the radiator return pipe and hose after it first fills the radiator
Now, there are a few issues with that drawing in addition to the small bleeder hose you mentioned first isn't shown on it.
The return hose from the autotrans cooler is shown connected to the wrong place, should connect to the large return hose going to top of thermostat housing. Not to the purple hose.
The purple hose is shown with a flow arrow FROM the coolant distributor but most of the time coolant flows the other way, into the coolant distributor from the left head. That is the primary cooling hose for the left head to feed the radiator. This flow reversal is performed by the bypass disc of the thermostat as the engine warms up.
Lastly, the large metal pipe from thermostat housing to the waterpump shouldn't really be labeled "bypass". It is always acting as the primary feed pipe to the waterpump once the system is filled.
Mark
| djkeev wrote: |
...............
I see the expansion tank flow as being top to bottom..... I always thought it was flowing up from the bottom!
The coolant is being drawn into the expansion tank via the small upper nipple and sucked out the large lower nipple because this lower nipple is connected to the metal suction pipe from the thermostat housing to the water pump.
Any air in the coolant will get trapped in the expansion tank in the "dead" space above the small upper intake nipple.
As the coolant warms and expands, this trapped air is forced out of the expansion tank and into the recovery tank behind the license plate. The air comes out along with any excess coolant being pushed out by hot liquid expansion.
Why the small sized "IN" nipple and the large exit nipple?
I can only guess that it regulates the coolant flow enough giving the air in the coolant a chance to rise out of the coolant as it "slowly" passes through the expansion tank.
I also think this is why the bleeder ring is only about a 1/4” inner diameter. To slow the flow and capture any air in the coolant as it passes through each cooling component. Air rises given the opportunity. But if air is trapped in liquid, it will get pushed along with the liquid.
As the system warms and the thermostat opens, the coolant flow is diverted through the radiator and the upper thermostat housing bleed hose comes into active play.
All this to say, that I believe the 1/4” NPT upper fitting on this tank is very adequate.
The air capturing aspect of the expansion tank is served just fine through the small bung size.
The expansion tank has LittLe to do with actual cooling (except that liquid under pressure has a HIGHER boiling point than water at atmospheric pressure has, by maintaining a steady system pressure, it does help regulate coolant temperature) It only handles trapped air removal and the regulation of expanding/contracting liquids pressure.
I hope this wordy post makes sense?
Dave |
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djkeev
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| Posted: Mon Dec 14, 2020 12:37 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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| crazyvwvanman wrote: |
Thanks for doing this as more understanding is helpful.
I think you covered the bleeder loop pretty well and yes coolant flow in the tank is from top to bottom.
The reason the lower output hose of the main tank needs to be much larger than the bleeder loop feeding into the tank is for when the cap is off and you are filling the system.
The constant bleeder loop coolant flow bypasses the radiator so is keep intentionally small to allow most flow to go through the radiator.
You are off a little on the small bleeder hose at the top of the thermostat cover. That has a manual valve that is intended to be opened only during cold filling and bleeding.
This lets trapped air escape as the waterpump fills the radiator return pipe and hose after it first fills the radiator
Now, there are a few issues with that drawing in addition to the small bleeder hose you mentioned first isn't shown on it.
The return hose from the autotrans cooler is shown connected to the wrong place, should connect to the large return hose going to top of thermostat housing. Not to the purple hose.
The purple hose is shown with a flow arrow FROM the coolant distributor but most of the time coolant flows the other way, into the coolant distributor from the left head. That is the primary cooling hose for the left head to feed the radiator. This flow reversal is performed by the bypass disc of the thermostat as the engine warms up.
Lastly, the large metal pipe from thermostat housing to the waterpump shouldn't really be labeled "bypass". It is always acting as the primary feed pipe to the waterpump once the system is filled.
Mark
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Good points!
Yes, that trans oil cooler returns into the large radiator hose that passes over the transaxle to the thermostat housing.
I didn't know that upper thermostat bleed hose was hooked to a manually operated valve. I know the valve was there but never had need to bleed it. I always thought it would just dribble past the threads as the radiator bleeder screw does.
I figured the larger return port at the tank was intended for increased draw out of the tank but never thought about it being needed to remove the cap while running!
The flow reversal of the purple hose from the thermostat housing to the coolant distributor tower makes complete sense!
This is also a reason to NEVER RUN WITHOUT A THERMOSTAT! The thermostat disc is what reverses the flow isn't it?
Once we definitively figure the flow pattern, a new coolant flow diagram needs to be drawn up.
Fixing the mistakes in this one and include the bleeder loop.
Dave
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DanHoug
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| Posted: Mon Dec 14, 2020 12:42 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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it'd be super sweet if someone with some draw program skills could incorporate these corrections as they come. i'd add:
- for the purple hose, have TWO arrows, one direction for open t stat, one for closed.
- label the 'oil cooler' as an 'oil HX' because it serves as an oil warmer for reduced cold start emissions more than anything. HX = heat exchanger
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kamzcab86
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| Posted: Mon Dec 14, 2020 1:10 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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| DanHoug wrote: |
| it'd be super sweet if someone with some draw program skills could incorporate these corrections as they come. |
Working on it.
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MarkWard
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| Posted: Mon Dec 14, 2020 1:18 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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The metal pipe running along the 3/4 cylinder, I don't believe labeling it as a bypass is correct. Its a main return/water pump inlet isn't it regardless of what the thermostat is doing? I don't know.
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djkeev
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Abscate
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| Posted: Mon Dec 14, 2020 1:41 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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Sweet Jesus. I’d forgotten that system had been secret;y designed by ghost engineers working for the Society for the Preservation of Hose Clamp Fitters in their Jubilee Year
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kamzcab86
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| Posted: Tue Dec 15, 2020 10:15 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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New illustration:
[Please go to Page 2 for current illustrations.]
Reply with any errors you see.
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djkeev
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| Posted: Wed Dec 16, 2020 12:48 am Post subject: Re: WBX 2.1 Coolant Circulation |
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That looks great!
Lots of work I'm sure.
Thoughts......
1) engine oil cooler flow direction.
I don't have the answer but I always thought the flow was cool returned from radiator coolant out of the thermostat housing? But I can totally see pressurized out of the pump being correct.
2) refill tank to expansion tank.
When hot the flow is a "burping" action from the expansion tank towards the refill tank.
3) out of expansion tank to water pump return pipe, modify arrow to make a right turn towards the water pump? Or would that be a given considering the flow indicated in the return pipe?
4) indicate heater valves before heaters?
5) label coolant return pipe from thermostat to water pump?
Overall..... great diagram!
Dave
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Abscate
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| Posted: Wed Dec 16, 2020 3:21 am Post subject: Re: WBX 2.1 Coolant Circulation |
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I never appreciated the complexity of the thermostat until you guys made these diagrams ( props to Kam for that nice one and a participation trophy for Dave)
Cold closed mode
The stat has to close off the return of the coolant from the radiator, leave the 12 pipe bypass open and shunt the 34 water to the pump as well
Hot open mode
Allow radiator return, close off 34 return to the pump and shunt to the radiator via the coolant distributor,
Running no thermostat I’m guessing removes enough impedance that radiator circulation suffers, with bad results.
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djkeev
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| Posted: Wed Dec 16, 2020 5:32 am Post subject: Re: WBX 2.1 Coolant Circulation |
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Abscate, my guess is that there is a Thermostat Closed drawing still in Kams computer. I am guessing that with a closed thermostat there is zero coolant flow through the automatic transmission oil cooler? The return loop of the cooler is tee'ed into the radiator return pipe.
And you are correct, removing the thermostat will create a coolant flow armageddon! The flow of coolant will be turbulent ineffective mess!
I have a thermostat housing housing that I will open today and post what is inside and how the coolant flow of the entire engine is regulated by this simple design.
This is NOT your old over heating Chevy where you simply pull out the stuck thermostat and create an unimpeded coolant flow!
I may take off a water pump too, and try to determine what the engine oil cooler flow is based upon the port design within the pump.
The pump pushes out to the right head so pushing to the oil cooler would be a simply design addition,
Dave
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AndyBees
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| Posted: Wed Dec 16, 2020 6:44 am Post subject: Re: WBX 2.1 Coolant Circulation |
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This is how I see and understand the 2.1 WBXer cooling system.
The Water Pump provides a constant "pressure" in the Water Pump Housing which has three Outlets, one to the Oil Cooler and to the Left and Right Heads.
Coolant “leaving” the two heads and oil cooler goes to the Distribution Tower (and Bleeder Ring). The Tower has one outlet with constant flow, the Bleeder Ring! Of course, there would also be constant flow thru the Heaters if the Valves are open. The Bleeder Ring will always have coolant flowing thru it if the system is full or near proper level. Thus, it’s other purpose, is constant circulation, which obviously includes the Expansion Tank, closed or open T-stat.
The T-stat only blocks “in-coming” coolant from the Radiator, which includes the Auto Transmission Cooler.
The flow of “hot” coolant across the T-stat from the left head and oil cooler is what makes it open. Keep in mind, T-stat “opening” is slow, not sudden. Thus, as coolant temp varies, so will the opening/closing of the T-stat vary.
Thanks Dave for all the good info, drawings, etc.
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crazyvwvanman
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| Posted: Wed Dec 16, 2020 8:02 am Post subject: Re: WBX 2.1 Coolant Circulation |
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It seems few fully consider the dual action of the WBX thermostat.
There are 2 disc on this type of thermostat. The primary disc OPENS to allow flow in the radiator loop.
The secondary disc CLOSES the bypass loop so coolant has to go through the radiator loop.
The flow direction in the bypass hose REVERSES as the secondary disc loses the bypass.
It would be nice if the thermostat housing passage details could be added to the drawing, showing how the bypass disc directs the flow.
Mark |
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MarkWard
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| Posted: Wed Dec 16, 2020 8:07 am Post subject: Re: WBX 2.1 Coolant Circulation |
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Now that I see it, if I had an automatic vanagon, I'd be looking at replumbing the trans cooler/exchanger.
In my travels, I notice my engine temp increases on uphill grinds. I imagine, the automatic is also getting warmer. An improved design might be to plumb both coolers/exchangers to the water pump discharge and into the heater return.
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djkeev
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| Posted: Wed Dec 16, 2020 1:03 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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Here is the Thermostat
The thermostat is designed to open at a preset temperature, the Vanagon is typically 80° C / 176° F
What does "open" mean?
There are metal discs mounted on a vertical shaft, on the Vanagon 2.1 there are two discs. This shaft moves up and down. It is controlled by a heat sensitive element that expands when hot.
The top disc when closed completely blocks all coolant from getting through.
Photo
When open, the shaft moves allowing the disc to withdraw and opens a circular gap, this allows coolant to pass freely through.
Photo
Now this 2.1 thermostat has a second disc mounted on the bottom of the thermostat.
When cold this disc is held open a distance of about 3/16” above a hole in the bottom of the thermostat housing allowing coolant to freely pass by and enter the lower hole.
Photo of thermostat, it is sitting upside down. The circular disc you see goes into the housing pointed down.
See the housing behind the thermostat? You can see the hole in the bottom of the housing.
This photo also shows the bottom side of the upper disc fully closed.
Here is a photo of the thermostat housing upright and the thermostat behind it, also upright and closed.
Look inside the housing, the hole on the bottom is the hole the thermostat covers and uncovers.......
Here is the thermostat in the housing with the upper cover removed. The thermostat is closed, blocking all flow.
The bottom of the thermostat housing is 1 1/8” deep when measured from the thermostat mounting lip.
On the closed (cold) thermostat the bottom sealing disc is 15/16” from the thermostat mounting lip. This leaves a 3/16” gap for coolant to flow through.
When the thermostat is hot, this lower disc moves down and completely seals off this bottom hole.
At the sane time the upper disc moves down and opens up to allow coolant from the radiator to flow into the thermostat housing This opening and closing redirects coolant flow through the thermostat assembly.
Dave
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djkeev
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| Posted: Wed Dec 16, 2020 1:03 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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Let's look at the thermostat housing.
It mounts on the front left of the engine, it is partly in the engine area and partly behind the firewall towards the transaxle.
Here it is bolted to the engine ......
This photo is what you can see in the engine area. The small hise with the silver clamp is the bleeder screw bleed Hose.
This small hose goes up and connects to the bleeder ring mounted high in the engine area.
The black circular disc you see is the bleeder valve. It is normally closed. You open it as you fill an empty cooling system with coolant. Opening allows the air in the thermostat housing to escape and not be trapped above the thermostat.
Look at the photo again, see the large cut off hose that is on the left?
You don't normally see or notice this hose. This hose is the return from the radiator.
Look again, see the large hose at the bottom of the photo? This hose is the return pipe to the water pump.
Another look at the photo and you will see a small hose (covered in grease) that goes off to the right in the photo. This is the engine oil cooler hose.
This photo shows even more!
See the two 10mm hex heads in the photo? There are two more you cannot see which hold the square upper thermostat cover to the lower thermostat housing.
Another photo from an angle you may not have ever seen. This is from the left rear axle looking back at the engine.
The hose at the top is the hose coming from the radiator.
The hose to the right is the feed to the water pump.
Below this hose is the coolant temperature sensor for the fuel injection.
The small hose is another bleeder hose. This connects to the bleeder ring.
The coolant sensor below this hose sends the coolant temperature to the dash temperature gauge.
To the left you will see a medium sized plastic nipple without a hose. This is the feed line from the coolant distribution tower over by the right head.
The rusty pipe below all of this is an exhaust pipe. Notice there us a heat shield on the bottom of the thermostat housing to protect against this heat source.
This photo also clearly shows the joint of the lower and the upper thermostat housing. (Horizontal seam below the hex heads clearly seen)
In the seam is where the thermostat is mounted.
Notice that the return hose from the radiator and the manual bleeder screw hose (not seen in this photo) are the only hoses above the thermostat.
Another photo from an angle you may not ever see, this is also from the transaxle side looking towards the engine.
This photo on the left side gives a good view of the feed nipple to the coolant distributor.
To the right is the bleed hose and temperature gauge sending unit.
The two 6mm allen head bolts hold the thermostat assembly to the left cylinder head.
Thermostat assembly, left side ......
Thermostat assembly, right side.....
Thermostat assembly, rear (engine side)
Thermostat assembly, front.....
Thermostat upper thermostat housing removed showing thermostat installed
Thermostat in housing, top view....
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kamzcab86
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| Posted: Wed Dec 16, 2020 2:09 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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| MarkWard wrote: |
| Now that I see it, if I had an automatic Vanagon, I'd be looking at replumbing the trans cooler/exchanger. |
Best to get rid of it altogether and install a genuine cooler or heat sink. 
| djkeev wrote: |
| Lots of work I'm sure. |
Yes, and thought I had lost it when the program said, "Can't open this file". Fortunately, figured out the problem.
| djkeev wrote: |
Thoughts......
1) engine oil cooler flow direction.
I always thought the flow was cool returned from radiator coolant out of the thermostat housing? |
Pump sucks coolant in from the left and expels it to the front and right. The illustration is purely a flow guide, not an exact component location guide. The actual oil cooler line exits the right side of the pump.
| djkeev wrote: |
| 3) out of expansion tank to water pump return pipe, modify arrow to make a right turn towards the water pump? |
Done. 
| djkeev wrote: |
| 4) indicate heater valves before heaters? |
That just complicates the illustration. Plus, if you don't know the valves are in the hot flow lines... probably shouldn't be working on your vehicle in the first place. [/end mild rant]
| djkeev wrote: |
| 5) label coolant return pipe from thermostat to water pump? |
The colors and arrows eliminate the need for any "pipe" and "hose" labels.
[Please go to page 2 for current illustrations.]
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~Kamz
1986 Cabriolet: www.Cabby-Info.com
1990 Vanagon Westfalia: Old Blue's Blog
2016 Golf GTI S
"Real knowledge is to know the extent of one's ignorance." - 孔子
Last edited by kamzcab86 on Thu Dec 17, 2020 1:09 pm; edited 4 times in total |
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djkeev
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Joined: September 30, 2007
Posts: 32625
Location: Reading Pennsylvania
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DanHoug
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Joined: December 05, 2016
Posts: 4794
Location: Bemidji, MN
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| Posted: Wed Dec 16, 2020 5:56 pm Post subject: Re: WBX 2.1 Coolant Circulation |
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i like what you've done with the t stat open and closed with regard to the purple color indicating mixing of the cool heater return and the hot head coolant!
it'd be nice to designate that the rad return is blocked off during t stat closed operation... maybe gray color to indicate still water? dunno. light blue to indicate a cold line that isn't moving?
but nice job, i like it!
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-dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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