eminenceN

Hello! This is my first post here at AudiWorld. So nice to finally join you guys. I recently bought an Audi A8L 2007 with the W12 engine. It is a really lovely car with a lot of extras and in a very good condition considered its age. I will upload some pictures later on

Anyway, why I am making this post is because it has problem getting up to temp while driving. I have made some research and read through all threads about this issue that I've come across. I still don't know where to start because I am not sure if is has a faulty thermostat, temp sensor or if there's anything else.

Descripion of my issue

- It is summer here in Sweden so it is around 20 degrees celsius outside. It still takes around 10km on the highway for the temp gauge to start to move from 50 degrees. After 20km it has reached 70 degrees celsius and there it stays. Does not matter if you keep 80km/h or 140km/h. In the city, the temp gauge slowly climbs towards 90 degrees. The temp sensor is not ''sailing''. It goes slowly up to 70, slowly up to 90 while standing still or while city driving, then slowly down to 70 again on the highway.

- First, I thought the temp sensor was faulty, so I prepared for changing that bastard. But the fact that the coolant temperature rises while driving in the city points towards an open thermostat.

- The heat output from the HVAC system is warm in the ''HI'' mode, but there's certainly not hot air coming from the vents. But this is my first A8 so i have no previous experience of how hot air the heating system can provide..

- I have replaced the thermostat for the transmission coolant circuit, but no improvement whatsoever.

- I have tried to see how the electric cooling fans are operating. Started the car up, turned the HVAC system OFF. No signs of ''jet fan''.

- I have searched for error codes with my Autel scan tool, but can't find any. Shouldn't a faulty thermostat or temp sensor give an error code?

So what do you guys think? Can I assume that the temp sensor shows the right temperature and that I have a faulty thermostat? Are there any more things I can test in order to narrow down the faulty part? I read some post in here where a guy pinned down a list of symptoms for faulty components in the W12 cooling system, I can't find it though...

Thanks in advance,
eminenceN

jsilas

Every piece of data you have points to a thermostat which has failed open. If it were my car, that's the first thing I'd inspect/replace.

Giovanni Giovino 6.0+6.0TT

+1...

Giovanni Giovino 6.0+6.0TT

No, and just for the record, many including myself have called the thermostat an "electrical thermostat" when in fact the thermostat itself is not electrical at all, it has no electrical moving parts at all, it is just as any other thermostat that opens and closes by the temperature of the coolant, what it DOES have is an electronic heating element that probes into the thermostats core wax area causing it to open faster when needed, but if the thermostat is stuck wide open, you will not achieve proper operating temperature.

MP4.2+6.0

As others replied, thermostat. If it were cooling sensor, I would expect either no reading and/or an error code when scanned, but not the slow to warm symptom. That really points to thermostat. Had it on mine too; failed slightly open.

eminenceN

Thank you guys for your replies! I also think it points at a faulty thermostat. I have decided to do the surgery myself and order the required parts at my Audi dealer next week.

The shopping list looks as follows:
- Thermostat housing 07D121111AN
- Intake manifold gasket 07C133238H
- 2x lower intake manifold gasket 07C129717D
- O-ring seals for the injectors (The injectors need to come off right?)

Have I missed something? And you with faulty thermostats, have you replaced them yourself and do you have any tips or advices to give?

The only thing I am a bit insecure about is how to fasten the thermostat housing and the intake manifolds. Do you have any information about the torque settings and in which order you should tight down the bolts?

I am so grateful for your answers!
//eminenceN

MP4.2+6.0

Yes, I DIY'ed. That and many other things. I didn't check part #'s, but list seems generally right. Of course if you are due for spark plug change by chance, this would be the time to do it too.

Frankly I just tighten all the bolts you mention by feel, albeit going on 40 years now. I use a torx screwdriver for intake bolts (T30 IIRC) to tighten most of way, which isn't going to strip anything. For first loosening and final tightening, I use a torx ¼" socket tip on a drive with a handle only about 4"/100mm long and snug them w/ that. Same sort of feel for thermostat related fasteners. Same tightening sequence as a cylinder head--basically from center outward as you go. The torques are low though given bolt size, so I really don't see warping anything.

Yes, the injectors do come off/out, at least on mine. It is really the rail that is in the way, but that seems to mean pulling everything. Apparently there are two fuel rail set ups, one where it has to come out, and one not. So far I think everyone posting on job over the years, except maybe one, had to pull it. I did mine w/ out replacing seals, but others have had leaks there that needed replacing. Be careful pulling the injectors to try not to break some plastic material that is along the body of the injector. I did on a few but still worked fine. To be clear, I never did figure out how to remove injectors from the rail, so levered both rail and injectors out all together as one assembly.

Jack88

I don't see that it's been mentioned, but if I recall correctly, all W12's have two thermostats that can fail. Not sure how'd you'd tell which one has failed, though.

TSHong

The other one is a thermostat in the trans cooler lines but only one case I've ever remember on all the boards. The regular tstat is usually the culprit. I did have to take my injectors off so I replaced both upper and lower orings. They are so cheap, so why not do both.

Giovanni Giovino 6.0+6.0TT

Hello All,
I thought I would just throw this out there in case anyone knows differently, as far as I know, the thermostat is only available as a complete unit, thermostat, heater, and housing, I am just wondering why, as the thermostat pops out of the housing like a serviceable item, see pics.

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