F265 Map Controlled Engine Thermostat Replacement (W12 - BAP)

[PanEuropean]

Hello All:

I reported the other day that my 'Check Engine Light' had illuminated - this was the first time that I have ever seen this light come on in over 2 years of Phaeton ownership. So, I dropped by my VW dealership and the technicians read the fault code out from the engine controller memory - it indicated that the F265 Map Controlled Engine Thermostat Replacement was showing an 'open circuit' condition. The consequence of this was that the engine was running quite hot (about 110°C, or 230°F).

Fault Code Generated by the Failed Thermostat

After some discussion, the Phaeton techs met with the parts department manager to determine what parts we would need to resolve this problem. Getting a new thermostat was only the tip of the iceberg. We found that we would also need quite a few seals, gaskets, and O-rings. So, the parts were ordered, the thermostat arrived by courier from Germany, and a week later, I brought the car back to have the problem solved. The technicians at my dealership - Volkswagen Richmond Hill, just north of Toronto, Canada - were kind enough to let me take pictures of the process so I could document how to go about replacing this thermostat. Special thanks go to Chris Melo for explaining to me what all the different parts were as he disassembled them.

First, a little background about this thermostat. It contains a wax material that melts at a temperature of 110°C. Normally, the wax is melted by an electrical current that is regulated by the master engine controller (controller 01). If the electrical current fails (an engine controller problem), or the electrical element in the thermostat fails (a thermostat problem), the wax will melt when the coolant temperature reaches 110°C. However, this is significantly warmer than the optimum temperature of the W12 coolant, which is between 88 and 90°C. The rationale behind using this rather complex thermostat design is that the engine controller can peremptorily open the thermostat to maintain target engine temperatures if the controller anticipates that things are going to get hot in the near future - for example, during full throttle acceleration. It is not necessary to wait until the coolant surrounding the thermostat actually heats up. The action taken by the engine controller is based on a 'map', or look-up table that is contained in the memory of the engine controller. It is necessary to use this type of design because of the complexity of the W12 engine coolant circuit.

Here is a bit of background information:

F265 Map Controlled Engine Thermostat Theory

The first step in the troubleshooting process was to connect the VW diagnostic scan tool to the Phaeton and follow the 'Guided Fault Finding' (GFF) steps that are presented in sequential order by the diagnostic scan tool. The first action was to check for the presence of electrical power being sent to the connector. The GFF presented this illustration:

The illustration above shows the electrical connector that feeds the cable running to the thermostat. This is connector T2t in the diagram below. The illustration accurately depicts the location of the connector. What it does not tell you is that the illustration was drawn with the engine removed from the car. In real life, that connector T2t is buried about six inches down the back of cylinder bank 2, and there is less than one inch of clearance between the aft face of bank 2 and the forward face of the steel engine compartment firewall. It is almost impossible to get access to it.

Wiring Diagram, showing detail of F265 Thermostat

After much deliberation, cussing, and scuffed knuckles, connector T2t was released from its bracket and opened up. Voltage coming from the supply side (T2t/1) was good, at 12.6 volts, but voltage across the circuit from the power supply to the controller was only 7 volts. This prompted the techs at my dealership to make an inquiry to the VW Techline (the technician support line) for clarification. The staff at techline suggested that a repair wire be run to a known good ground, so, this was done, everything was reassembled, and another diagnostic scan was made. The problem was still there - an open circuit. This pretty much proved that the thermostat itself was defective, and the next step in the GFF process was to measure the resistance at the thermostat itself. At this point, it was clear that the engine had to come apart - again. The car was then moved from the diagnostic area back to the dis-assembly area.

Ready for surgery

Battery Maintainer Hooked Up

This thermostat is mounted right in the middle of the engine block. The screen-shot from the diagnostic scan tool shows the location. The illustration is drawn from the perspective of someone standing behind the engine, which is a bit confusing - normally the technician stands in front of the car when he or she works on the engine.

Location of the F265 thermostat and its electrical connector

Engine dis-assembly was quite straightforward. First, the large air ducts leading from the air filters to the throttle bodies were removed. This allowed the outer pieces of the upper intake plenum to be separated from the center piece and moved slightly outboard.

Digging in...

The throttle bodies, visible after the air ducts have been removed

The two outer parts of the upper intake plenum were then moved outboard a few inches. It was not necessary (nor would it be desirable) to actually remove them from the engine bay.

Next, Chris removed the bolts holding the middle portion of the intake plenum onto the engine. These are the bolts that are visible whenever you open the hood.

Once those bolts had been removed, the center portion of the intake plenum could be lifted off. There is a reason why there are two people holding on to it. The two outboard parts of the plenum, the center part (shown below), and the lower portion of the plenum (visible later) are all constructed as a matched set and individually serial numbered. They are magnesium castings, finished and ported by hand, and the entire assembly - four parts in total - costs over $10,000 USD. Hence the reason two people are holding on to it. It was taken to a secure location out of the way of passing traffic for storage.

It was now possible to look directly at the lower portion of the intake plenum. The lower portion had to come off as well, because the thermostat is underneath it. The thick wiggly stainless steel tube is the fuel rail. Now that you can see where it sits - buried in the engine - it is easier to understand why the W12 engine is so sensitive to fuel boiling problems associated with the low volatility fuels that are sold in North America during the winter - or, fuel boiling as a result of ethanol that has been added to the gasoline at the refinery. The thick black wiring harness is the power supply to the fuel injectors. The eight connectors across the back of the engine are from the eight different oxygen sensors in the engine. The dirt visible in some of the holes of the lower intake plenum is oil that has deposited on the plenum. The oil comes from the positive crankcase ventilation system.

The twelve holes in middle of the photo above lead to the cylinders of the engine, so, the very first action after removing the upper intake plenum was to put protective tape over the holes to ensure that nothing could fall into the engine.

As you can see from close inspection of the photo above, there is very little clearance - less than 1 mm - available to remove the lower intake plenum. It is necessary to remove the electrical connectors from the bank 1 and 4 fuel injectors, and to remove the stainless steel clips that secure the bank 2 and 3 fuel injectors in place. Only after this is done can the lower intake plenum be reluctantly wiggled out.

A fuel injector connector
Press down on the middle part to release the locking mechanism

The little metal clips that need to be removed from bank 2 and 3 injectors
This is done only to provide sufficient space to remove the lower intake plenum.

Finally, it is possible to remove all the bolts holding the lower intake plenum in place, and remove the plenum and the rubber gaskets that fit between it and the engine block.

By now, fasteners were beginning to accumulate on the workbench. They are laid out in the order they were removed, beginning at the left.

This is what the engine looked like after the lower intake plenum was removed. The F265 thermostat is front and center, partially hidden beneath a black metal tube (I think that tube is called the 'aorta').

The GFF screen shows where the internal resistance of the thermostat needs to be checked - at the connector on the thermostat body.

The result of the check was not good - the thermostat itself showed an open circuit (infinite resistance). This proved that it was defective.

By comparison, the new thermostat showed very little internal resistance. The GFF diagnostic screen gave a desired value, and the new thermostat was right in the middle of the desired range. Note the change in the design of the new thermostat. Instead of having a connector on the thermostat body, the cable is integrated into the thermostat, and the cable is made of a heavier material, better able to resist the high temperatures in this area of the engine. A very good example of continuous product improvement by VW.

Removal of the thermostat was pretty simple. It is held in place by about half a dozen fasteners. There are coolant hoses on each end of it, and the front coolant hose has a 'quick disconnect' clip on it.

Out comes the old thermostat. Not much coolant was lost - only about 500 ml.

Every single fastener that had been removed had a specified torque value for re-installation - hence the printout of the instructions that can be seen in some of the photos above. Besides doing a good job of illustrating the assembly of the components, the printout of the Repair Manual provided the torque value for every fastener during the reassembly process.

Reassembly was quite straightforward, and proceeded faster than the dis-assembly process. We were all grateful to Blaine, the parts manager, for his careful research and planning a week earlier, because we had all the new gaskets and seals we required on hand for the reassembly process.

Sadly, when the very last fastener was being torqued, it snapped. This is a very special fastener - we think it is made out of magnesium. It is very, very lightweight, and almost a pure white colour inside. We now have to contact the engine manufacturing plant in Germany for their advice before attempting to remove the base of the fastener from the lower intake plenum. I have to go back to Europe next week, and if necessary, I can take the lower intake plenum with me and send it to the factory by courier. Being made out of magnesium, it doesn't weigh very much...

Michael

The 'Aw, ****' moment...

[jimay]

Did they partially drain the coolant?

The screw may come out with an ez out.

[PanEuropean]

No, no-one deliberately attempted to drain coolant. About half a liter spilled out when the thermostat was removed. That was much less than anyone had expected.

The tech is a little bit concerned about that broken fastener. It appears that the fastener is made of magnesium. Plus, the cost of not getting it out correctly on the first attempt would be $10,000+ of parts replacement. We're waiting for advice to come from the Quality Control staff at the engine plant in Germany where the engine was made. If they can work up a repair scheme for removing the broken fastener, great, the staff at my dealership will follow that scheme. Otherwise, I'll take the part (the lower intake plenum) back to the engine plant and have the specialists there remove the broken fastener. As long as I am in Europe, Africa, etc. I don't need the Phaeton to be functional.

Michael

[murphybaileysam]

Wow! Following that procedure was like watching a triple bypass coronary artery surgery.
Was your only symptom of the problem that the car was running hot when your "check engine" light came on?
Any idea as to what was the cause of the part failure?
How many miles do you have on your car now?

[Itzmann]

Michael, it was very interesting to see your description of the work and engine pieces. A $10K piece of metal! Who would have thought? I would have guessed these were forged parts costing... $500?

In March of this year I had the same check engine light problem. Here is what wrote:

"Exhaust light:
found code P1292 for thermostat, checked pwr going to F265. OK.
Chinese to me. Remv'd & Chck'd ECM too, was fine. They ended up replacing:

1 unit 07D-121-111-AK Thermostat
2 units 07C-129-717-D Gasket

My webpage source says each gasket is $99.95 msrp and can't find the thermostat."

http://forums.vwvortex.com/zer...42087

I don't understand whether the thermostat they replaced is F265 or a different thermostat. Would you happen to know whether F265 corresponds to part No. 07D-121-111-AK?

Thanks!

Modified by Itzmann at 9:48 PM 12-26-2006


Modified by Itzmann at 9:54 PM 12-26-2006

[PanEuropean]

Francisco:

I have not seen the part number yet because my copy of the work order has not yet arrived in the mail. However, there is only one F265 thermostat in the W12 engine, and that is the one illustrated above.

But, I did have a quick look in the parts catalog, and the part number of the F265 thermostat is 07D 121 111. It is at suffix AP revision now - perhaps that indicates the version that has the cable going directly into the thermostat body, rather than the previous version that had a two pin connector on the thermostat body. It is about a $400 part.

Michael


Modified by PanEuropean at 1:50 AM 12-27-2006

[PanEuropean]

Quote, originally posted by murphybaileysam »

. Was your only symptom of the problem that the car was running hot when your "check engine" light came on? Any idea as to what was the cause of the part failure? How many miles do you have on your car now?

Correct, the only indication I had of the problem was the 'check engine' light and the thermostat showing warmer than normal (105° to 110° instead of the normal 90°). I have no idea why the part failed - probably just 'one of those things', because the only other owner who has reported having that same part replaced is Francisco. The car is at 55,000 kilometers now - I think that is about 35,000 miles.

Michael

[Itzmann]

Quote, originally posted by PanEuropean »

Francisco: I have not seen the part number yet because my copy of the work order has not yet arrived in the mail.

Thank you for the follow up. Once you receive the work order, would you kindly share the list of other gaskets or parts your mechanic required in order to complete the F265 replacement?

Thanks in advance.

[Motorista]

Michael,
Thank you so much for the fascinating and wonderfully detailed post: I feel I really learned a great deal from it! Reading this, I once again am amazed at:
1) How critical is a methodical, "surgical" approach to successfully repairing and maintaining our cars. I always take this approach in my own car work, even though it inevitably results in every job taking much longer than originally anticipated, but I can afford it because I do not have to make a living out of my repairs. However, very, very few professional shops are willing and/or able to take such an approach: your dealer is clearly the exception!
2) How complex the Phaeton really is. Years ago, I had to replace the thermostat in my '91 Legend. I remember being vexed at how long it took me (about 4 hours), including draining the coolant, disassembling the throttle body to gain access to one of the bolts securing the thermostat, and refilling and purging the circuit. Well, clearly a piece of cake compared to this. Also, in most cars a faulty thermostat will stay open, which means the engine runs cooler: this is how I came aware of the fault in my Legend. In the Phaeton, instead, the engine runs hotter! very interesting.

One final question: do you know the part number and how I can acquire a fenders/grille protector like the one your dealer is using? I need to get ready for when I will take over the maintenance when my car will be off warranty....
Stefano

[PanEuropean]

Hi Stefano:

Chris (the engine specialist at my VW dealer) is a very precise guy. He had not taken a W12 engine apart prior to mine, so, I think he was 'extra precise' when he did this work for the first time. After it was all done, he told me that it was a pretty straightforward engine to work on, but the very tight fit around the sides, back, and front of the engine made it difficult to get at anything that you couldn't reach by going in from the top.

What impressed me the most about the whole exercise was the teamwork involved. As I mentioned in the earlier post, the work began about 10 days before disassembly started when a conference was held with the parts specialist, Blaine. Blaine did all the research to find out exactly what gaskets, seals, o-rings, etc. would be needed, and he was the one who made sure everything was there and ready when Chris started in on the disassembly. A really experienced parts specialist makes all the difference in the world - the parts guys are the ones who can make the tech's job look easy.

As for the bib - it is classified as a 'Volkswagen Special Tool', and has a tool number that you can see on the side of it - VAS 6133. Normally the lead technician in a dealership is the person who looks after ordering special tools - they are typically not ordered by the parts specialist. I happen to know the person at VW Auburn Hills who is responsible for special tools (he helped us get the 50 Trim Removal Tools that VW donated to us at our last Phaeton owner GTG) - I will write him and ask what the cost of the bib is. I kind of suspect it is expensive, simply because it is a limited production item.

Michael

Bib for Phaeton

[Motorista]

Thank you, Michael. I'm definitely interested, unless the price is prohibitive. Also in the trim removal tool, if you cna let me know the price. My birthday is not too far away....
Stefano

[PanEuropean]

Hi Stefano:

The trim tools are very inexpensive, about $2 each. Perhaps we can get Rich at OEM Plus to stock those for us. Or, just wait for the next Phaeton owner GTG - VW of America has been quite nice to us in the past and donated trim tools for distribution at the GTGs.

The bib, sadly, is very expensive. It lists at USD $378.- I have asked Rich to look into seeing if he can get them for us at a lower price by taking advantage of his volume purchasing. FYI, here's a direct link to the bib on the Volkswagon of America Special Tools Website (this website is run by Snap-On for VW of A): Phaeton Bib.

Michael

[Motorista]

Thank you Michael. link did not work for me though, probably because I am not a registered dealer. In any case, Rich, if you read this pls. post or IM me with some estimates.
Regarding A VOA GTG, michael do you have any sense when it might happen? I missed the one last year (or was it the year before?) but I'd love the opportunity to attend the next.
Stefano

[PanEuropean]

Hi Stefano:

I haven't discussed dates for the 2007 North American GTG with anyone yet. I would prefer to hold it in Auburn Hills, at VW of America headquarters, but I first need to talk to some people at VW and see if they are interested in hosting the GTG.

I'm returning to Canada Saturday, maybe I can get some inquiries made during February.

So far as the link above goes, you don't have to be a dealer - look carefully at the web page and you will see a provision to log on as a member of the public. You'll still see everything, nothing is hidden, it's just that you can't order on an 'invoice me later' basis unless you are a dealer.

Michael

[V10NRB]

Michael,

How is the repair going on your car, we have not heard anything on the forum for weeks, is it fixed now.

cheers

Neil

[PanEuropean]

Hi Neil:

I left for Switzerland a few days after the bolt broke, and I have not been back to Canada since. My VW dealer advises me that they have received a complete set of replacement bolts to hold the big intake assembly in place (in other words, all the bolts that are visible on the top), and they have also received a repair scheme from the plant in Germany that builds the engine.

So, it should be pretty simple to get things fixed - I just have to take the car to the dealership. I will be going back to Canada this weekend.

By coincidence, I also received an email today from Snap On tools. The account manager at Snap On who is responsible for the Volkswagen special tools product line has seen this thread and is now aware of our interest in the protective bib for the front of the Phaeton. He has proposed a one-time special price of US $275.- per bib for the Phaeton owners. This price will eventually be made public, but we have about a week's advance notice of it. So, if anyone wants to buy a bib, please let me know here on the thread, so I can give Snap On an estimate of what the demand will be. I realize that $275 might sound like a lot of money, but this is quite a well made, very sturdy and durable bib - the materials are top quality in every respect - and I think it is worth that price. It can also be used on other vehicles - my VW dealer often uses the Phaeton bib to protect the front end of Touaregs.

Michael

[chrisj428]

Quote, originally posted by V10NRB »

How is the repair going on your car, we have not heard anything on the forum for weeks, is it fixed now.

I believe it's done. I spoke to an Advisor at Michael's dealership today to get a few details on the repair (we're doing the same thing on a customer's car at my dealership right now) and when I referenced Michael's car, his first comment was, "Do you have his car at your dealership now?", which leads me to believe it's done & gone. (Who would have picked it up is beyond me as I'm confident Mrs. PanEuropean would just as soon let it sit there... )

[PanEuropean]

Quote, originally posted by chrisj428 »

I believe it's done...

Ah - that will be a nice surprise, then. I have absolute trust in the staff at my dealership, so if they somehow got their hands on the car and replaced the bolt, great, I'm delighted.

I have lots of stuff to work on when I get back, and at the top of the list is finishing the television retrofit and the phone retrofit.

Michael

[pirateat50]

I hate to even say it: My CEL came on again last week.

Turns out it was the F265 Map Controlled Engine Thermostat.
There is no longer a trained Phaeton tech at my dealership (I think the saga of my torque converter did him in!), but the "substitute" tech did a great job with it.

I have approximately 41K on the car and it was built shortly after PanEuropean's W12. I hope this is not a trend.

I also requested a replacement of my dim J523 Infotainment unit. The shifter plate cracked on reassembly, so I am waiting for the part. I needed Dr. David to teach the tech the delicate touch!

This forum continues to provide great info for this Phaeton owner. Thanks guys! You too, PC!

Modified by pirateat50 at 8:15 PM 2-14-2007

[PanEuropean]

Quote, originally posted by pirateat50 »

...I hope this is not a trend.

Hi David:

I don't think enough of these thermostats have failed yet to be able to call it a trend, however, we now know of three F265 thermostat failures (yours, mine, and a customer at Chris B's dealership in Chicago). This represents about 1% of the NAR W12 fleet, but our sample size is too small to draw any reliable conclusions.

I'll ask the Dresden staff if they have noticed any trends when I attend the German Phaeton owner GTG at Dresden this coming April. That thermostat does live in a pretty warm environment, and I noticed that there has been a design change to the electrical connector on it, to move the connector out of the high-heat area.

At least we have a write-up (above) that explains the replacement process to VW technicians who are doing it for the first time. It's a pretty straightforward repair, the only noteworthy issues are these three:

1) It is a real PITA to get access to the electrical connector for the F265 at the rear of the passenger side cylinder banks. You need very small hands, and a good collection of small dental pick tools.

2) The bolts that hold the magnesium intake manifold cover in place (the bolts that are visible down the centerline when you first open the hood, before any dis-assembly) are very fragile, because they are also magnesium. The tech needs to use a high-quality bit (e.g. Snap-On) that is not deformed in any way, and the tech needs to ensure that the bit is always kept perfectly vertical above each fastener as it is being loosened or tightened.

3) A very delicate touch is needed to gently bend the tangs on the three injector bodies closest to the lower manifold on the passenger side, to allow the lower manifold to be rotated out of position. The lower manifold can be removed without having to totally remove injectors, but the tech has to have a very light touch to manipulate the injector bodies.

For what it's worth, the flat-rate book pays about 10 hours for this repair, and a competent technician who has never done it before - but, who has the ability to read and follow directions - can get the job done in about 4 hours, working at a relaxed pace.

Michael

[beambuzz]

Two things...

Where do you pull your manual-looking photos from? Is there some site that I have not heard about, perhaps a subscription site?

2nd thing-check your IM history, I sent you some photos for clarification of another question.

Thanks for all your input, the Phaeton group is lucky to have you as a mod/poster.
-Tim

[pirateat50]

Quote, originally posted by PanEuropean »

1) It is a real PITA to get access to the electrical connector for the F265 at the rear of the passenger side cylinder banks. You need very small hands, and a good collection of small dental pick tools. Michael

That might explain all the scratches on my tech's hands and forearms. I thought his cat had thrown a hissy fit.

[PanEuropean]

Quote, originally posted by beambuzz »

Where do you pull your manual-looking photos from?

Hi Tim:

In this post, illustrations have come from three sources.

The pictures that look like screen-shots of the Volkswagen Diagnostic Scan tool (5051B) are, well, screen-shots of the 'Guided Functions' portion of the information that the scan tool presents. This is quite an amazing diagnostic tool, it is like a VAG-COM and a repair manual all rolled into one.

Screen-Shot of 5051B Diagnostic Scan Tool

The illustrations that incorporate both text and illustrations are excerpted from the "Self-Study Guides" that Volkswagen publishes for their technicians. These booklets are not intended for public distribution, but anyone can purchase the booklets - or purchase a licence to download and view them as PDF files - from ErWin, which is Volkswagen Europe's technical publications center. The publications are copyright by VW, so we cannot reproduce the whole book (or large portions of the book) here on the forum, but it is my belief that occasionally using small excerpts from these publications in the context of a larger original work is "fair use" under the Berne Convention, which is the international treaty that deals with copyright issues.

Example of an excerpt of a Self-Study Guide

The wiring diagrams are available to the public, all you have to do is subscribe to the Phaeton Maintenance Manual, which you can do through Bentley Publishers, the company that distributes this material to the public. You then get exactly the same material that the VW dealerships get - the repair manual, wiring diagrams, technical bulletins, the works. Again, all the stuff is copyright, but I think it is OK to reproduce small excerpts in the context of a larger original work, as long as we are not publishing the whole darn thing.

Example of a Wiring Diagram Excerpt (from the Bentley Manual)
(I have added the text that is in red)

[beambuzz]

Thanks, didn't know of the erWin site
though I didn't see any info on the type1, hopefully they'll add some.

-Tim

[PanEuropean]

Quote, originally posted by beambuzz »

...I didn't see any info on the type1...

Hi Tim:

When you say "type 1", do you mean the original Beetle? Those have pretty much turned into collector cars in Germany now, and as a result, VW themselves get very little demand for service and support - enthusiasts and restorers are getting all the work. VW still supplies an astonishing number of parts for the original Beetle, though.

Michael

[bobschneider]

Michael, I had my themostat replaced a couple of weeks ago, in response to my check engine light coming on, so that's 4 among the members of this board. But a couple of days later, the CEL came back on, which is why my car is about to have its torque converter replaced. I dunno if I really had both faults, or if my dealer did the more likely problem first. But they have a lot of experence with Phaetons, and I deal directly with the service manager, so I think they know what they're doing.

[PanEuropean]

Hi Bob:

Funny you should mention the torque converter.

In the last few days - during my drive from Toronto to Detroit to Chicago and back - I have had the 'Check Engine Light' come on three times, and in each case, the fault has been as follows:

17125 - Torque Converter Clutch: Stuck OFF / No Power being transferred
P0741 - 003 - Mechanical Failure - MIL ON

That is the same fault code that the TB about the torque converter (TB 32-06-01) refers to. The sad thing is that the car operates perfectly - the only problem is this darn light coming on! I have been clearing the fault code memory and turning the light off - it seems that the fault is only momentary, it only lasts for a second or two when you start up - but the darn light keeps coming back on.

I am going to ask one of our 'forum friends' at Auburn Hills if there is any way this problem can be overcome without having to replace the torque converter. Not only is the torque converter awfully expensive, repairs like this can be a bit of a nuisance for owners who do not have "Phaeton Friendly" VW dealerships nearby.

Michael

[pirateat50]

Well, after a week of waiting on the shifter plate part to come in, they call to say the car is ready. The only problem is that now they have cracked the wood panel the surrounds the cup holders and runs all the way up under the dash and back to the rear seat. So, now that is on order, but at least I am driving the car.

And people think Job had patience.

[PanEuropean]

Quote, originally posted by pirateat50 »

...The only problem is that now they have cracked the wood panel the surrounds the cup holders and runs all the way up under the dash and back to the rear seat...

Oh no... that part is murder to change. You have to do a huge amount of disassembly to change it, starting with removing both front seats and then getting really serious about taking things apart once those are out of the way.

To be perfectly honest, my suggestion is that you just take delivery of the new part and leave it in the box. Keep it, if you ever sell the car, you can provide the new (undamaged) part to the subsequent buyer. If the car is on a lease and you will be returning the car to the same dealer, then don't even bother to replace it - just get an agreement from the dealer that they won't take issue with the broken part when you bring the car back. That will be a really easy agreement to negotiate, because the replacement part alone costs well over $1,000.

FWIW, the very same part on my car cracked last weekend as a result of extreme cold temperatures - when I saw it, my first thought was 'Oh sh*t, not that part!" I still have not made up my mind what to do about it - it is well over a full day of labour to replace that part, and the possibilities of consequential damages are very, very high.

Michael

Disassembly required to replace that part
I have done this, and it ain't no fun.

[pirateat50]

Thanks for the heads-up. I am really ready to scream now. I do not think anyone in that dealership has the patience and skill needed to handle the replacement. I don't know how much the cracks will affect future value of the vehicle. I would like it fixed, but may just take the part. . .perhaps the Phaeton helpline folks could direct me to a shop qualified to handle it.

[PanEuropean]

My personal suggestion is 'just take the part', if your primary concern is resale value rather than present appearance of the part with the crack. In other words, if the crack is minor and you can live with it, take the part and don't go down the installation path.

Michael

[pirateat50]

Everytime I see the cracks (two of them), it bugs the hell out of me. I am trying to adapt. Maybe in a week I can consider just taking the part.

Either way, thank you for your most valued advice.

[diab]

Quote, originally posted by bobschneider »

Michael, I had my themostat replaced a couple of weeks ago, in response to my check engine light coming on, so that's 4 among the members of this board. But a couple of days later, the CEL came back on, which is why my car is about to have its torque converter replaced. I dunno if I really had both faults, or if my dealer did the more likely problem first. But they have a lot of experence with Phaetons, and I deal directly with the service manager, so I think they know what they're doing.

I have a W8 at 68k and the MIL came on. So I took it to autozone to have Diag read and came back P0599. That lead me over to a post in passatworld forums where they talk about measuring the resistance of the heater-resistor. So I bought a bentley manual and removed my upper and lower intake. My resistance measured 9.3 ohms which seems to be out of the 14-18 range recommended.
Anyway ordered the thermostat which appears to be same one used for W12 and I will be replacing it soon.
BTW, the intake was not as much trouble as you would think. I put it back together and have been driving it while waiting on the part.

I also had my torque convereter replaced at 38k under warranty. 18 hours of labor and torque converter. Not sure if W12 and W8 uses same converter. Mine had something to do with the hydraulics that engages the plates to direct contact when engine and drive train are cruising at the same speed. My light wnet on and off and I felt small engine revs when the plates disengaged at cruising speed.

Seems similar to my problems and are very similar to other I've read

[VWAffe]

Hi,

It's nice to hear of dealer techs that will take due care when working on your car. Unfortunately, I've not met one yet.

My W8 has thrown a fault code indicating there is a short in the thermostat, so I've been doing a little research of my own prior to digging into it. I have to make a minor correction to your background below, based on what I've learned from SSP 222 - Electrically Regulated Cooling System. (I've got a copy of the original German - not sure if it was ever published in english)

Originally developed for the 1.6 L 4-cylinder APF motor, the electrically controlled thermostat actually functions the opposite of what you laid out below. When energized, the wax is heated and expands, extending a plunger that mechanically opens the thermostat "large circuit" to the radiator, cooling the engine. Per the SSP (actual temperatures on the W engines may be different), this is done to cool the engine to between 85 and 95 C during high motor load and/or high RPM... which enhances power output by minimizing intake air heating (an old hot-rodding trick). During part-throttle cruising, by allowing the plunger to retract, the motor temperature is regulated to be higher (between 95-110 C!) to enhance efficiency and minimize CO and unburned HC emissions. The ECU regulates the position of the thermostat using pulse-width modulation to the heater element. In the event of current or heating element failure, the fail-safe mode is that your motor will run in the hotter regime, but is still regulated to not overheat past 110 C. So no fear... 110C is not overheated; just normal for part-throttle cruising.

Quote, originally posted by PanEuropean »

First, a little background about this thermostat. It contains a wax material that melts at a temperature of 110°C. Normally, the wax is melted by an electrical current that is regulated by the master engine controller (controller 01). If the electrical current fails (an engine controller problem), or the electrical element in the thermostat fails (a thermostat problem), the wax will melt when the coolant temperature reaches 110°C. However, this is significantly warmer than the optimum temperature of the W12 coolant, which is between 88 and 90°C. The rationale behind using this rather complex thermostat design is that the engine controller can peremptorily open the thermostat to maintain target engine temperatures if the controller anticipates that things are going to get hot in the near future - for example, during full throttle acceleration. It is not necessary to wait until the coolant surrounding the thermostat actually heats up. The action taken by the engine controller is based on a 'map', or look-up table that is contained in the memory of the engine controller. It is necessary to use this type of design because of the complexity of the W12 engine coolant circuit.

Modified by VWAffe at 8:08 AM 2-13-2008

[PanEuropean]

Photos re-hosted.