nyrobbie77

Hi all. I just purchased a '97 A8 4.2 quattro with 160k miles. The heat doesn't work at all. The controls all seem to work, the system changes modes from defrost to vents to floor, as well as the fan speed changes as requested. The engine reaches normal operating temp and does not overheat.

the place i bought it from put a new t-stat in, and supposedly replaced the bleeder screws and flushed the coolant system. they assumed that it must be a head gasket issue, which i don't agree with. engine doesn't overheat, no coolant out the tailpipe, no coolant smell in exhaust, engine oil is dirty but no milkshake coolant mix.

I did notice that after letting the car heat up, the upper heater hose was not warm, only the lower heater hose. these were the two staggered hoses on the driverside of the firewall. I opened up the two bleeder screws with the engine running at temp and coolant sprayed out of both. after that the upper hose seemed to be hot, but might just have been heat soak.

the coolant resevoir - coolant was nice and pink, but had a little oily residue around the edges. i took the car for a quick drive (about half mile) after it got to temp and now all the coolant in the resevoir is kind of dark. I took a picture and will attach.

i will be pulling the plugs to see if theres any sign of burning coolant and will try bleeding the system again. think either there is a air pocket still or the heater core may be plugged.

any advice or ideas are much appreciated. thanks in advance!

silverd2

Hard to say, but you might have multiple problems...maybe unrelated(?).

Clogged heater cores could be caused by past use of stop leak (TERRIBLE stuff..always with a consequence) or a past mistake (even if drained since) mixing of G-12 (pink coolant) with another kind, which causes thick brown sludge to form, which can clog a core and degrade plastic fittings. Evidence of stop leak use (even if drained since) can usually be found in the coolant reservoir...shine a flashlight up against it and look for dark accumulations at low spots, esp around the level switch.

If it's a clogged/contaminated blockage problem, a good chemical flush might cure the problem.

The fact that you feel a hot and a cool heater hose, makes it sound less likely that it's the temp control flaps in the interior heater/Ac housing...Vagcom hooked up to OBD diagnostics will read every flap position to confirm working or failed.

Worst case (well, expensive and tough to change) for no heat, is a failure of the monster in the photo...coolant pump/valve unit, found between the brake booster and the intake vent for heating/AC.

As for oil mixing with coolant (if that's what we're seeing in the coolant tank?), one other place other than the head-gaskets, that can mix them, is the oil cooler (bolted to lower right side of engine block, behind alternator)...breached coils inside the cooler could mix oil and coolant...It's a coolant cooled oil cooler.


D2coolantvalves.jpg?t=1318168271

nyrobbie77

thanks for the info. i also noticed the hose going to the top of the reservoir tank is leaking coolant, whoever crimped the clamp did it improperly and it leaks fairly steadily when the engine is running. opening the cap after engine is at temp relieves some pressure, but far less than one would think. the place i bought it from sprayed engine shine everywhere, so wondering if some got into the reservoir. before i let it ran, the coolant in the tank was very pink, with just a little oily residue on the sides. there is some dark junk stuck to the top of the reservoir that i can see. i plan to remove the tank, clean it and reinstall.

i am pretty sure the oil cooler is leaking, atleast externally. when the engine is running there is a decent leak from the right front engine area onto the ground. haven't put it up on ramps yet to check it out. if it is, i'll do a chemical flush to try to remedy the coolant pipes.

is the upper heater hose the inlet or the outlet? always thought the lower was the outlet, but thats the one that is hot. the upper did seem hot after i cracked open the bleeder, so maybe it was just some air trapped.

will the free version of vag com scan the HVAC? registered version? or do i have to go full monty and get the $250 version?

is there a test i can do for the coolant pump? like if i disconnect one of the lines to see if it is pushing fluid or not?

sorry for all the questions. i have done a lot of searching. lots of posts similar to this, but no one updates with solutions. hate that.

thanks again!

nyrobbie77

meant to say that i'll do the chemical flush before repairing the oil cooler leak as i have to drain the coolant anyway.

silverd2

The oil cooler is actually prone to leaking coolant, more likely than oil, due to an ill-conceived plastic pipe (which decomposes and breaks eventually) connecting the cooler with the engine block. Oil rarely ever leaks from the outside of the cooler (rubber seal in tight contact to cooler and block), but "could", esp from the oil pressure sensor on top of cooler...sometimes profusely.
The 32V engines are also prone oil leaks from the oil pump pulley...front rightish of the engine. Also valve cover gaskets are prone to leaks on 32V engine...maybe running down from there or a leaking cam end seal on that side(?).

I believe (pretty sure) the upper heater hose is coolant into the valve unit (then cores).

I've got the free version of vagcom and mine can't read the hvac module...but I get an error message, rather than "stated" blocked access..so, I'm not sure if it's my cheap cable connection or not available(?).

I don't know much about testing the pump/valve unit...more about how it works. The 2 domes are solenoids that open/close valves to each of your 2 heater cores (dual climate zone)....the pump helps some during warm-up to speed hot coolant to the cores...plus it runs the restore feature on the climate control. If you didn't know, when the engine is fully warm, you can hit "rest" on the climate control after the engine is off (with 30 minutes) and you'll get up to 12 minutes of fan and heat usage, with engine (and ignition switch) shut off.

So, you may want to try the restore feature, with engine warm and off, to see what happens...listen for pump under the hood.
Many have disconnected the system (pump...not sure about valves?) and had normal heat afterwards...just no restore feature. So, you may also want to try disconnecting elec plug for the pump/valve unit (cylinder shaped plug w/purple, I believe)...then try heat...don't know if the valves have a default open or closed setting(?)

nyrobbie77

spent some time with the audi today. pulled all 8 plugs, all look good, no signs of burning coolant. pulled the coolant reservoir and tried to clean it. lots of oily crap on the sides that won't come clean. used dish soap but wasn't dawn, so maybe not enough grease cutter. mbe i will try to soak it in some degreaser for a couple days.

left valve cover is definately leaking, can't tell where the leak is from on the right side. only leaks when the engines running. won't leave any drops on the ground even when parked for 2 days, but let it run and i'll have a spot about the size of a saucer. definately coming higher than the oil cooler, so maybe either the cam seals or oil pump.

i tried the restore feature after i got the engine hot. it works, can hear the pump and it blows air, just cold. again noted that the upper heater hose is cold, lower is hot. if i open the bleeder the upper one will get slightly warm.

I found something else, the lower radiator hose is stone cold as well. its cold all the way from the block to the radiator. so am thinking i either have a bad t-stat thats not opening or blockage in the block or radiator. does this sound about right?

i ordered a cable and downloaded vag com lite. don't think its going to help for this problem, but will be good to have anyway.

nyrobbie77

just reread my post. the LOWER hose is cold, upper is hot.

ps, i hate lazy mechanics. bolts and screws missing all over, not anywhere important, but come on, don't ya wonder where all the extra fasteners go? someone routed the throttle cable on top of the actuator rod going to the TB, surprised it didn't rub thru. missing the lower engine/splash shield as well.

silverd2

1st, there's a fuse for the elec pump (pump/valve unit)...I think #8 in your fuse panel...and another fuse for the valves, #5. Each is 15amps...all this according to the wiring diagram in Bentley.
Your fuse box should be different from mine, so don't know which row of fuses, if you have multiple rows, like '00 model and up. My'01 has just one fuse for both pump and valves, in 3rd row.

Did you notice if the pump itself was running during your "restore" test?

The fact that you have a hot upper heater hose and cold lower, tells you that either pump is not running and or the valves are not opening or the cores are clogged.

The pump/valve unit gets it orders from the climate control head (and power from another fuse set), so if other CC functions are working, I wouldn't suspect the control head..."possible" but unlikely and rare.

Yep, those plastic belly pans are hard to find for any year D2 A8... a lot of people lookin for em. EBay is packed with A4 and A6 pans, but nothing for A8....new ones are at least $260 and higher than that most suppliers.
They definitely serve a purpose...controlled engine compartment airflow, aerodynamics, often great for detecting leaks (and their location).
...and you can't skip a car across a pond at high speed without one

nyrobbie77

ok, i got my posts all screwed up. the upper heater hose is cold, lower is hot. the lower RADIATOR hose is stone cold and upper is hot. think thats pointing to a bad t-stat, which supposedly was replaced to try to fix the no-heat.

during the restore i could hear the electric pump running. don't think thats a problem.

as the lower radiator hose is cold, am thinking that electrics aren't my problem. gonna start with a new oem tstat. will make sure i do a boil test first to make sure it opens properly.

thanks again, have a great christma-hanu-kwanza-kah, or simply happy holidays!

nyrobbie77

picked up an OEM tstat today. got it from a VW only dealer. guy pretty much sounded like i was bothering him, said "ugh, its prolly audi only..." mbe will have to go out of my way to the audi dealer next time.

drained the radiator, disconnected both radiator hoses, and found one of the torx head bolts for the water outlet stripped out. got the other one out ok tho. had to use my dremel tool to grind the head off the bolt, then some vice grips to remove the remainder of the bolt. what should've taken an hour max took close to 3hrs..

previous mechanic used a cheap "made in china" tstat. apparantly was too lazy to get a gasket for it and just RTV'd the tstat in place. got the old tstat out ok, cleaned up the reminance of the RTV and installed the new tstat with gasket and two new bolts. even wire wheeled all the built up corrosion on the water outlet neck.

after all together, refilled the coolant and let it warm up. after a couple minutes the tstat opened then refilled the reservoir. both radiator hoses are not getting warm/hot, previously only the upper radiator hose would get hot. so atleast i fixed that...

still no heat in the cabin tho. the upper heater hose is still cold, lower gets hot. not getting anything to come out of the upper heater hose bleeder screw. i can remove it with the engine hot and nothing comes out, can't see any coolant flowing. can't hear the coolant pump run when i put it in REST mode now either.

so either i have some blockage in the heater cores, or the valves in the coolant pump are stuck closed. will add a chemical flush and try to back flush the heater cores tomorrow. if that doesn't solve it, will pull the coolant pump.

does it sound like i'm on the right track?