W12 Overheating slowly

   #21  

jyoung8607

FoRT
Verified
Joined
Feb 25, 2014
Messages
2,510
Reaction score
4,089
Location
Cincinnati, OH
VCDS Serial number
C?ID=25607
A belated welcome to Team Phaeton! We demand to be taken seriously!

This Group 130 data (taken over about 40mins, 72F ambient outside, driving 55-70mph the whole time) shows the first t-stat call seems to have an effect on the output coolant but later, especially towards the end the input and output are diverging big time which somewhat says to me, that t-stat isn't actually opening at least when the engine gets nice and warm. Is that a fair diagnosis?
Good problem description and data collection, well done.

Did you ever get this one figured out? Could indeed be a partial flow restriction at the thermostat, though you are definitely getting at least some opening. It could also be one of the auxiliary water pumps, which the W12 does depend on. IIRC your W12 will have four water pumps: one mechanical, two aux electrical, and one more electrical built-in to the Climatronic heater core distribution block. Could also be something as simple as a trapped air bubble deep in the system. If the system has ever been opened, the factory repair manuals specify it must be drained and filled with a vacuum tool because the W12 cooling system is hilarious spaghetti with no design facility for bleeding air from high points.

I'm very new to VW vehicles so just want 2nd opinions, because that t-stat on this car is $300 plus 3-5hrs labor. (which is low for a Phaeton w12, easy job right!???)
Indeed it should be reasonably easy as far as W12 jobs go. I'm pretty sure I could do it in two hours working at a pretty leisurely pace.
 
   #22  

Larry Manton

Verified VCDS User
Verified
Joined
May 19, 2016
Messages
552
Reaction score
296
Location
USA
VCDS Serial number
C?ID=112505
73blazer. Nobody stated how long you have had this car?

Have seen TDI that coolant refill was never put in via vacuum (air lift) and had ECT codes for years, then magically disappeared during timing belt change and coolant installed correctly.

Would be inclined to drain it, properly load it again and seen what happens. Also some system will leak under vacuum and not under pressure, or the other way also. Load it with vac, then let it sit for a bit and see if it bleeds off. JMO, and like belly buttons everyone has one.

Good luck
 
   #23  

73blazer

Verified VCDS User
Verified
Joined
Mar 11, 2020
Messages
16
Reaction score
14
Location
MI, USA
VCDS Serial number
C?ID=397169
It has been a long trek and still working on it. I replaced the t-stat then found a leak in the plate behind the t-stat. Ordered that, new one has ribs in it, so apparently the plate warps.
Then pressure test revealed a leak in the coolant fitting that connects to the tstat. THe BAP cars have two smaller nipples off the main 90. One leads to the recovery resevoir the other to the aux radiator. The small nipple was leaking. Removed, that nipple broke off completely plastic there is all soft and heavily discolored. (other fittings in the system are fine), hose not available (fitting not sold separately, part of hose assembly) anywhere on earth, and no room to really re-plumb. The fitting was also leaking on the top, where it was very thin in an area. I drilled and tapped a new smaller nipple into that boss. That part was fixed, but the fitting was still leaking on the top, and the material was basically defective. No expoxy was gonna fix that, nothing to adhere to.
So I sent that off for CT scan and beefed up the profile in the thin area and submitted for Carbon DLS 3d print in cyanate ester (better than nylon 6 GF which was the OEM material) . Got those, installed, pressure test. Hold 20lbs for hrs. needle doesn't move. awesome. I also replaced both sensors since the intakes were off and they were both easy to get at.
BUttoned her back up and fired it up. No codes so I put everytyhing back together right. I also removed alot of the lower hoses to attempt to drain the system so I could change as much coolant as I could I believe I got about 4 gallons out at least.

But....its still overheating. But in a different manner. I think now I do have air in the system, no I didn't use a vacuum filler. I might get one and do that. Now it goes to 200F and sticks, for 10-15miles, then...rises very rapidly to 240 or so. If you shut it off and let it sit for a min, turn it on, it's where it was for 5 seconds or so, then immediately drops to 200F where it should be. Then drive and it starts rising again. So I think air.

Old and new "plates" behind the t-stat:


Here's the old broke fitting under pressure leaking (sprayed soap water on it) with my drilled and tapped new smaller nipple:

Old fitting profile look how thin at the top and how discolored that thing is, all the plastic in the system is not discolored like that, and it was all soft like you could gouge with your fingernal:

Here's my new fitting.


New fitting profile (alot beefier up top there!):


Printed fitting in cyanate ester


So now I can only hope it's air, otherwise, I'm not sure where to look. If it was water pump, it seems it'd blow past 200F without stopping and never come back under any circumstance.
 
Last edited:
   #24  

jyoung8607

FoRT
Verified
Joined
Feb 25, 2014
Messages
2,510
Reaction score
4,089
Location
Cincinnati, OH
VCDS Serial number
C?ID=25607
I replaced the t-stat then found a leak in the plate behind the t-stat. Ordered that, new one has ribs in it, so apparently the plate warps.
Then pressure test revealed a leak in the coolant fitting that connects to the tstat. THe BAP cars have two smaller nipples off the main 90. One leads to the recovery resevoir the other to the aux radiator. The small nipple was leaking. Removed, that nipple broke off completely plastic there is all soft and heavily discolored. (other fittings in the system are fine), hose not available (fitting not sold separately, part of hose assembly) anywhere on earth, and no room to really re-plumb. The fitting was also leaking on the top, where it was very thin in an area. I drilled and tapped a new smaller nipple into that boss. That part was fixed, but the fitting was still leaking on the top, and the material was basically defective. No expoxy was gonna fix that, nothing to adhere to.
So I sent that off for CT scan and beefed up the profile in the thin area and submitted for Carbon DLS 3d print in cyanate ester (better than nylon 6 GF which was the OEM material) . Got those, installed, pressure test. Hold 20lbs for hrs. needle doesn't move. awesome. I also replaced both sensors since the intakes were off and they were both easy to get at.
Very good work on debugging leaks in the system. Failure to pressurize can definitely result in overheating, so that was critical.

You kind of sent me down a rabbit hole on PL24. Not your fault, I'm unnaturally susceptible to that sort of thing to start with, and my ears perk up in a really unpleasant way when someone starts talking about Phaeton parts going NLA. I just spent more than an hour doing stare and compare on BAP (yours) vs BRP (mine):



Looks like some of the hose assemblies and fittings are truly NLA for BAP. I see your bad fitting was never available alone, as you're aware (I saw your VWVortex thread) it came as part of a hose assembly. Your version of the left-side upper rad hose is 3D0 122 051 K, the one for cars with the heavy-duty cooling / second radiator option, was dropped from the catalog on Jun 1 2020. Bad timing for you. :( As you may have seen, the version for cars without the second radiator 3D0 122 051 C is still available.

In your case, you could have swapped the still-good -K fitting onto a new -C assembly, but that won't solve everything for everyone. Looks like BOTH variants of the right-side lower rad hose are NLA for BAP, and other bits and pieces have gone NLA as well. So that's a real fucking problem for BAP owners going forward. Unfortunately it's hard to be completely shocked since BAP equipped Phaetons last rolled off the production line 15 years ago.

One way to deal with that is what you did, which BTW is amazing work. I love it. In the future, you might even do a bit of business selling them. Another way... I'm 99% sure you could switch to BRP parts. Studying PL24, it turns out Volkswagen thinks W12 cooling was over-engineered or something, because BRP simply never had the option for an aux radiator. It uses the exact same main radiator as BAP, until a much later facelift when it gets a thinner main radiator. Maybe they stopped worrying about Dr. Piech going full send across the Sahara, IDK. But I think you can safely lose the aux radiator, once you replumb around it.

If one were to remove the aux radiator from a BAP cooling loop using BAP parts, you'd ordinarily need to swap out three hoses and a bracket. The BRP cooling arrangement is a bit different, but not drastically so, some of the parts are shared. The bracket (21 non-HD BAP :: 39A on BRP) and two of the hoses (4 non-HD BAP :: 39 BRP, 38 non-HD BAP :: 1 BRP) are the exact same parts you'd use for a BRP. The third is the NLA right-side lower rad hose which doesn't directly map. For that, referencing the diagrams below, I'm reasonably confident you could replace BAP 43, 15 with BRP 35, 36, 37, 34 and associated clamps/fasteners.

Phaeton with BRP (or rather, BRN/BTT for non-US emissions) rolled off the production line all the way through the end, model-year 2016, so parts availability should be good for quite a while. This looks so ridiculously close to exact-fit that I wonder if that's why they felt okay discontinuing the BAP parts. I wonder if this is official at some level, if there's a tech note/ETKA bulletin/supersession we haven't seen.

BUttoned her back up and fired it up. No codes so I put everytyhing back together right. I also removed alot of the lower hoses to attempt to drain the system so I could change as much coolant as I could I believe I got about 4 gallons out at least.

But....its still overheating. But in a different manner. I think now I do have air in the system, no I didn't use a vacuum filler. I might get one and do that. Now it goes to 200F and sticks, for 10-15miles, then...rises very rapidly to 240 or so. If you shut it off and let it sit for a min, turn it on, it's where it was for 5 seconds or so, then immediately drops to 200F where it should be. Then drive and it starts rising again. So I think air.

So now I can only hope it's air, otherwise, I'm not sure where to look. If it was water pump, it seems it'd blow past 200F without stopping and never come back under any circumstance.
Almost certainly air stalling one or more water pumps, judging both by your symptoms and your process. The factory service manuals are very explicit about vacuum filling. It simply doesn't have traditional burp points or a burp procedure.
 
Last edited:
   #25  

73blazer

Verified VCDS User
Verified
Joined
Mar 11, 2020
Messages
16
Reaction score
14
Location
MI, USA
VCDS Serial number
C?ID=397169
Yeah I know the service manual says vacuum fill. But there's lots of things those manuals say use some $$$ vag tool and it's not really needed, coupled with many people's reports of these w12's just fill, run it , drive it, fill, watch it for a few days and eventually the air will work itself out.aka...as most normal cars I've dealt with in my life work.
I can get a vacuum filler, there's some generic ones that most report work well with VW's. Being 50 years old, i seem to have gotten by in life without one, until now.
I did pop the heater hose line where it passes tthru the cowl and forced several pints of fluid in there. It drove this morning for longer than it did yesterday before rising, and it's hotter out today. So...i'm still hoping it's air in the system.
The C hose has a fitting with just the smaller nipple that goes to the recovery resevoir. So, sans the larger nipple that goes to the AUX rad. There's no room to re-plumb much, but you could get rid of some plumbing if you ditched the aux rad. The BRP hose routing elsewhere is quite different than the BAP ones, including how the 2nd elec. pump is plumbed in. So not sure ditching the aux rad just yet would be a good idea, it may be a can of worms.
My other thought is perhaps the main water pump is the culrpit, and the aux pump is keeping it cool, until it really warms up at which point it can't keep up. But it is behaving differently than before, before was just a slow steady rise. Now it's stick at 200 for a 10-15miles then rise super quick. First things first, lets see if I can bleed this thing.
 
   #26  

jyoung8607

FoRT
Verified
Joined
Feb 25, 2014
Messages
2,510
Reaction score
4,089
Location
Cincinnati, OH
VCDS Serial number
C?ID=25607
I can get a vacuum filler, there's some generic ones that most report work well with VW's. Being 50 years old, i seem to have gotten by in life without one, until now.
I have a generic Schwaben one as well. I used it on my ATQ (V6 30V) Passat a couple times, it's nice to have, but I knew right where the two designed-in factory bleed points were (one screw in a metal pipe, one tiny hole in a metal hose barb you expose by backing off the hose) to fill it up manually, quick and easy if I was in such a mood. You can absolutely do that on a lot of simpler vehicles. The W12, on the other hand, is spaghetti confetti and just doesn't have any bleeder screws or other designated high spots for air bleed.

many people's reports of these w12's just fill, run it , drive it, fill, watch it for a few days and eventually the air will work itself out.
Oh, the air will work its way out...





... eventually. :D

Sorry, not trying to Debbie Downer the job you're doing, just saying try the Easy Mode if you're having trouble with Hard Mode.
 
Last edited:
   #28  

73blazer

Verified VCDS User
Verified
Joined
Mar 11, 2020
Messages
16
Reaction score
14
Location
MI, USA
VCDS Serial number
C?ID=397169
He he he NostraJackASS has flanges due to forethought when new & as private stock and indeed others can be adapted!
Even available in aluminum...... :eek:
I looked at adapting other connectors. Spent days combing over others actually. That wasn't gonna work here. The angles had to be what they were, had to have the big and little nipples off the main sweep and there is no room on the w12 to start re-routing anything. mm Below is belt, mm in front is rad,mm above is intake and behind is block, I barely had room to add a screw clamp in place of the perma clamp the oem fitting had on it as that fitting was part of the hose assembly, just the addition of that screw on there made it that much tougher to get in and install. There is no possible way to start adding or re-routing plumbing or changing angles with other fittings without basically turning it into a BRP car sans aux radiator.
If your saying he had the exact one needed, it was never sold individually, it was part of the hose assembly ans this one specific to 2002-2005 BAP w12 hot country or w/aux radiator which all NA w12's were. Plus the OEM is flawed, with that thin profile up top, it will go at some point. Mine was additionaly flawed because it was soft and mushy and basically disintegrating mabey all of them aren't like that, but certinaly the supplier for that thing had at least a bad batch because the rest of the plastic fittings in the system didn't exhibit this problem. My new fitting is improved profile and stronger material than nylon the oem uses. .

It was air in the system. While I agree now.... this system should be charged by vacuum, and I have a tool coming, but in the meantime I just kept heating it up (driving) , them injecting coolant into the high point at the heater hose where it enters the cowl in the drivers side back of the engine, drive again until it did it, and eventually it stopped doing it. Last night I went 120miles and needle never moved off of 200F as it should.
I don't actually think it was actually overheating either, I'd jump out with my IR gun when it was doing it and couldn't find anything much over 200 anywhere on the cooling system or block for that matter. I think those air bubbles hit the sensors and play games with how the computer interprets it. Physics says, you can't increase the thermal mass of 17l of coolant from 200 to 240f in 3 seconds, and bring it back down to 200, in seconds like it was doing.

So, to the original overheating problem. I ended up replacing both sensors since they were much simplier to get at while the intake was off doing the t-stat. So it might have been one or both of the sensors, the t-stat, or the two minor leaks it had. or the combination of any of those.... But it holds pressure for hours now, no leaks, and the overheating issue is gone. I think....problem is solved!
 
Last edited:
   #29  

jyoung8607

FoRT
Verified
Joined
Feb 25, 2014
Messages
2,510
Reaction score
4,089
Location
Cincinnati, OH
VCDS Serial number
C?ID=25607
The C hose has a fitting with just the smaller nipple that goes to the recovery resevoir. So, sans the larger nipple that goes to the AUX rad. There's no room to re-plumb much, but you could get rid of some plumbing if you ditched the aux rad.
Agreed.

The BRP hose routing elsewhere is quite different than the BAP ones, including how the 2nd elec. pump is plumbed in. So not sure ditching the aux rad just yet would be a good idea, it may be a can of worms.
Replumbing a BAP for non-heavy-duty cooling is perfectly valid, that's why I think this will work. The only problem is, one of the three hoses you'd need for replumb involved is NLA (different from the one you had a problem with).

The only component that would become truly "BRP" parts (instead of parts that are identical between BAP non-HD and BRP) is one point-to-point hose, no branches from the lower right radiator outlet to the coolant manifold at the back of the engine block. The radiator end is the same, the manifold end is the same. It just becomes four pieces instead of two, and the twisty-turny bits may be shaped a little different, so it's just a matter of whether the new twisty-turny bits affect physical fitment along the route.
 
Last edited:
Top