sullyj

Hurrah! I now have heat and the issue was a faulty heater control valve. I initially put a used one on the car back in Feb'17 and frankly, I believe the tech who did the diagnosis should have been able to see that the unit was faulty rather than tell me one of the actuators in the dash was the issue. new part was incredibly pricey ($1600) but it was that or freeze this winter. Now if I can just get the oil sludge from continuing to pop up in my overflow coolant tank!

MP4.2+6.0

That's a good result in the end--it works.

Consider the possibility the oil sludge may not be that, but rather the remnants of putrid water crap from your heater core(s). Thus, maybe go in again and flush them by running water in the reverse of normal flow--basically clamp a hose into the heater returns and unlock the hoses on the heater supply. I recall it coming up before with anoher member. That is, in his case backflushing fixed the clog he had and what came out was nasty from the pics.

sullyj

Thanks my friend. Yesterday my coolant light came on after driving about 3 miles. Coolant level was perfect, but the sludge was on surface in the overflow tank. Drove car 15 miles this morning and no warning light. Car will go to shop tomorrow for another flush and fingers crossed.

sullyj

Okay, so I have the oil sludge issue resolved. Here on the east coast weather has been miserably cold (6 degrees today) and it seems to now take forever for the interior heat to get to a comfortable level. It takes at least 15 minutes of driving before temperature gauge hits dead center and cabin heat is still moderate at best. The interior heat will become comfortable only after at least 30 minutes of driving and I'm getting close to giving up on ever getting this effectively resolved. System has been flushed twice and techs telling me there is no issue with heater core. As indicated previously a new heater control valve was installed last month, but outdoor temperatures were not nearly this cold then. Have owned several cars over the years and none have frustrated me as much as the A8's I've owned (D2 and D3). Fell in love with the aesthetics of these cars, but reliability is certainly not one of their strengths. If anyone has any suggestions I'm all ears!

sullyj

By the way, my earlier post is for a 4.2 engine. Thanks.

jeffkruse

By the way, I have the same issue with my 2004 Audi A8 and have done a couple of flushes, and nothing helps, I get no error codes as well. Please help.

Shark_V8

Easy thing to check is air flow through the HVAC box /unit. If these flaps are open you'll get decent air flow even if your recirc air flap is non-functional which is a common issue.

Look at the flaps that bring fresh air into the car. They are under the cabin air filter cover , under hood at base of windscreen.

BTW the cabin air filter can be cleaned and re-used, the thing is well built. I just hosed the dust out, dried it and reinstall.

MP4.2+6.0

Two more ideas:

1. Bad main cooling system thermostat. If yours is a 2008 and thus FSI, I am guessing it will have one of the electronically assisted ones. Also called MAP assisted. You would have to check/confirm. W12 has one of those and when mine failed it was very slow to warm up, and was not able to maintain heat for sustained driving at 0F--as I found out one night driving 60 miles on freeway to another city in -6 to +4F weather. Only then would it finally trigger a code for cooling system malfunction. Whether MAP: or simpler regular thermostat, if it fails partially open, car will be slow to warm.

2. Another research project. Again you have the later 4.2 per the original post title (2008), which seems little documented here for any variations that apply only to the FSI motor. On both S8's and W12's there is a virtually unknown inline auxiliarythermostat in the cooling system. It deals with coolant flow to the transmission. Several years ago a W12'er in very cold Scandanavia had lots of heating issues on a W12, after owning a prior one that was fine. He traced at least some of the cold blooded stuff to that auxiliary thermostat after I described it to him. Someone with an S8 replaced it at one point too IIRC. It is found on W12's and S8's in an easy to access water line down under the car near a transmission fluid cooler. Again, just a hunch it may have crept into the 4.2FSI. S8 was sort of the first FSI entry point for D3's, and my sense is it shares cooling system similarities with S8 since both have the newer gear drive set ups for most of the auxiliary functions, including water pump IIRC.

jeffkruse

it is just cold not warm. What is really weird is if the fan is on low, I can get warmer heat. So I keep it on low then turn my heated seats on to keep me warmer in this cold weather. By the way the AC works just fine

Canadagord

There are two thermostats... (ask me how I know) I was having very similar problems, (taking for ever to come to temp, zero to no heat from any of the vents etc.) But replaced part # 4E0121113 (or similar, don't have the exact number here at work but this is what it looks like...) and now have full heat, car comes up to temp quickly (even when it like -26C here in Ottawa) and I have a very warm car... So, yes there are two thermostats, teh engine one and this one... My indi called it an "inline" thermostat...