Brozee

Hey guys,

Often times I can figure things out on my own or through searching. 2005 A8 with 204,000 miles now. Runs like a champ. Recently went for a drive and noticed the heat wasn't working, at all. The air conditioning works great, the blower fan is blowing properly. Due to it being cold and me not having time I took it to my European shop to have it looked at. Here is what has been performed so far.

1. Heater core flushed 3 times, some sediment came out
2. Replaced Heater valve with a used but clean unit from eBay ($150), it was $1500 new... no way I was buying a new unit
3. No air in the system, the hoses are warm going into the heater core, and all flaps are functioning properly and the heater valve unit is performing as it should.

My mechanic said he can't be fully sure but he has narrowed it down to him thinking the heater cores themselves are the culprit and are bad. They are extremely expensive so I want to see if that sounds about right to you guys. Cheapest I could find them is for $371 a piece, and of course this car has 2...

So if the heater cores indeed need to be replaced, would the similar VW variant work, I cannot tell any more other than having other referenced part numbers when searching it. If so, the VW part number is significantly cheaper, $145 a piece, and it is also the part number that fits the VW Phaeton, which is near identical to the A8. Please advise.

VW Heater Core:
https://www.jimellisvwparts.com/prod...3D0898030.html

Audi Heater Core:
https://www.audiatlantaparts.com/p/H...D0898030B.html

MP4.2+6.0

I don't have answers to your questions, but two thoughts/questions:

1. Did you have the cores flushed backwards? That is, also do it in reverse through the return hose to the cores instead of the supply hose--water or low pressure air? See this thread for volvopentaman's experiences on W12 side and what finally worked for him: https://www.audiworld.com/forums/a8-...-heat-2913702/

2. Being in MI and all...are you sure the thermostat has been diagnosed in full? That is, if stuck open and MI type temps still at this time of year, it will be slow to warm with a stuck open thermostat. Does temp gauge read normally at midpoint + when you are experiencing the issue?

As you will see from the last pictures in that linked thread, heater cores are not something to be taken lightly work wise on many vehicles.

Brozee

Unfortunately after speaking with my mechanic this morning, he did indeed do all of the above. So I'm going to either bite the bullet now, or wait until next winter to replace them. Any word on if the VW equivalent would work?

2004A8L

Bypass one, one at a time see which one is blocked

Brozee

I ended up waiting until next year to replace as I'm not about to drop that much down right before summer. On my way back i noticed heat coming out of the vents now. So now the heat does work, but only to a degree. It doesn't get very hot or heat like it should, but there is at least some weak heat now. Any further advice?

MP4.2+6.0

2005 4.2...

The early ones are difficult to bleed. Audi changed the cooling system sometime around or during 2005 in part to deal with it, changing the hose layout and connections to radiator IIRC. If all your mechanic is doing is what I do at home--open the bleed screws one time with motor running--it may not be adequate on the early ones. Your driving experience w/ it coming back is suggesting some of the same. It may need the pressure bleeding technique and equipment. Did your shop really do that? Poor man's method to approximate is likely still open bleed screws, but do it several times over some miles and time to let air work through system better.

volvopentaman

Have had the same struggle with 2006 W12 with 246000km and now 2008 W12 with 360-370000km (odo shows 262000km but at least 106000km is missing). We have NOT had any of these problems on friends 2005 (mfg 2004) 4,0TDI. I suspect the cast iron block saving the game there!, and the problems seems to be only with gas engines (V6/V8 TDI has cast iron block on all engine models AFAIK)

On my current i have flushed both heater cores 6 separate times (last january and march, now in december, january, february, march and today), both forward and backwards, with compressed air, with garden hose, with caustic soda/lye (we call it Lut in swedish and Lipeä in finnish), the stuff that will dissolve most organic materia, and also with vinegar and vinegar essence. Treatments from 5min to 1h have been tried. Always cures the problem for a couple weeks.

Using kickdown function (full RPM on engine) seems to get **** into the heater cores and blowing them with compressed air always cures the problem for a fwe weeks. I replaced my coolant a few months ago, absolutely no help. Did not the the engine block empty, will try that next. Suspect there is debris in the block, that travels to the cores at kickdown when the water pump spins up in RPM, and this always clogs the cores.

4D0898030B is the right spare part number, D2 ones will not fit (may try to sell them to the D3)

USED ONE so you see what it looks like, I strongly advice to buy new one!!!
https://www.ebay.co.uk/itm/AUDI-A8L-...-/131655630755

I actually removed passenger side core today, like litterarly 10min job!!! And driver side i had 2/3 out (need to remove brake pedal to get it all way out).
Tools needed:
Torx TX20
Torx TX15
7mm 1/4" socket driver with 150 or 200mm extender
13mm with 300mm extender for brake peadal

1.To remove globve box, 2 screws behind CD changer pockets!!! and 3 in upper corner of glovebox, 2 TX20 behind end of dash cover and 2 in each corner of under glovebox. Total 9pc TX20. Take out 2 multiplugs (one from CD changer and one from right corner of glovebox
2. To remove passenger (RHS) heater core unscrew TX15 screw that keeps CORE in place, unscrew clamps that hold core heat pipes in place with 7mm socket (a bit nasty to put back, but can be done), undo electric connector that is fitted in core holding bracket, and also incoming temp sensor.
3. Unbolt MMI screen control unit (2pc TX20), you DO NOT NEED TO UNPLUG cables, just leave it hanging!
4. Drag out heater core after twisting the pipes aside.

Driver side is same operation, EXCEPT you must remove knee cover.
1.This cover is fastened with 5pc TX20 (one on each side of steering column behind dash trim, just pry out the dash trim), one on lower right corner, and 2pc TX20 behind dash end cover. Undo ignition lock cable, ODB port, light switch AND floor light (if fitted) cable.
2. Same stuff needs to come off except no electrical connections here, so 2pc pipe clamps (7mm), 1 bracket (TX15) AND brake peadal (IIRC was 4PC 13mm)

Brozee

Update:

This winter proved the same, no heat again. The fix was to replace both heater cores, to the sum of $$$$. However, I had one last attempt at a thorough flush of both, over a two day period. Ended up having tons of gunk come out of the cores, heat is now restored and working. I'd say about 75% effectiveness, after $400. Much better than the alternative of replacing them.