Fixed my "no heat" problem.

[JMRQuattro]

Ya, I've been bleeding the system like crazy, so much that I have constant smell of burning coolant when I drive the past month or 2. YUM! I guess I'll go back and keep bleeding it and bleeding it and then bleed it some more! I'm sure hoping that this fixes the problem. How come us Germans can make such great things and ef up a cooling system so bad in this model of car? (and I hear the same generation Passat is just as bad)

Do you have any visible leaks or are you noticing coolant loss at all? And did you replace the j-plug when you did your thermostat? If you're having to bleed it that much you either have a massive amount of air in the system or it's finding it's way back in somewhere. And the passat is just as bad because it has the same longitudinal 1.8t in it. The a4 and the passat are basically the same car.

[iceman2k]

Do you have any visible leaks or are you noticing coolant loss at all? And did you replace the j-plug when you did your thermostat? If you're having to bleed it that much you either have a massive amount of air in the system or it's finding it's way back in somewhere. And the passat is just as bad because it has the same longitudinal 1.8t in it. The a4 and the passat are basically the same car.

When I did my heater core I asked them to do the J plug too. They charged me for it on my invoice but I'm kind of wondering if they did replace it. I kind of had it out with that shop a month ago and went to a different place to get my thermostat done.

I'm not seeing any coolant loss and I can't see any dry coolant around the J plug. But with all the white on my engine / engine bay right now from all the coolant the past few weeks i have been bleeding, its hard to tell if anything is leaking. But from when I had the heater core done last December to October when I had the thermostat done, my coolant didn't drop and I didn't have to fill it up once.

[JMRQuattro]

When I did my heater core I asked them to do the J plug too. They charged me for it on my invoice but I'm kind of wondering if they did replace it. I kind of had it out with that shop a month ago and went to a different place to get my thermostat done.

I'm not seeing any coolant loss and I can't see any dry coolant around the J plug. But with all the white on my engine / engine bay right now from all the coolant the past few weeks i have been bleeding, its hard to tell if anything is leaking. But from when I had the heater core done last December to October when I had the thermostat done, my coolant didn't drop and I didn't have to fill it up once.

It's possible that if it's the j-plug that it could just be an extremely slow leak or leaking almost no coolant at all. When it gets hot it expands, preventing any coolant from leaking, but once the engine is cold it can suck air in and be nothing more than a very slow drip, if it's leaking at all. You should check it just to make sure since it sounds like these symptoms didn't occur until after your thermostat was replaced.

Just continue to bleed the air as Old Guy described in the OP (in addition, turn the heater on high temp/low fan). You may want to spend more time bleeding to make sure you've got all of the air out of the system at once, rather than bleeding small amounts at a time between driving. If/when you get all the air out (your heat is working properly; there is no pressure when taking off the coolant reservoir cap at operating temp; you have a solid stream of coolant coming out of the bleeder screw) and the problem comes back, then you know that air is being introduced somewhere in the system and you need to look elsewhere for a leak.

[old guy]

As you have already figured out the heating system in the B6 doesn’t work very well at idle. The coolant has to flow from the rear coolant flange down to the bottom of the heater core, push up through the core and then back down to the lower return hard pipe. An air bubble anywhere along the way will seriously reduce or even stop the flow at idle.


Here’s why: There are two forces acting on the coolant flow. There is the “push” of coolant into the heater core that comes from the rear coolant flange and then there is the “pull” of coolant coming out of the core from the water pump via the lower hard pipe. When you are at idle it is critical that you have both these forces acting in unison if you expect to get any flow through the heater core.


At idle the “push” is minimized simply because the water pump is turning very slow and isn’t putting out much circulation pressure. So it’s critical that the water pump can exert some “pull” from the other side. An air bubble anywhere in the heater circuit will cause a break in the coolant column and consequently the water pump cannot exert any of the “pull” needed to circulate coolant through the heater core and the circulation stops. Once you start driving the car the “push” force becomes strong enough to force circulation through the core and you get your heat back.


So the obvious question is how to get all the air out of the heater circuit? Basically I have found that there are two places to address. The obvious one is the bleeder port on the exit side of the heater core where you pull back on the upper hose to expose the port and purge any air present. The other area often gets overlooked. It’s where the heater core return hose connects with the lower hard pipe. If you look closely at the connection you will notice that the connection forms an upside down “U” shape. A perfect shape to retain an air bubble. That’s all it takes to break the “pull” force needed at idle to keep the coolant flowing through the heater core.


It’s not too difficult to purge. First open the reservoir cap. Then crack open the connection between the coolant return hose and lower hard pipe. Pull back the wire clip and gently wiggle the plastic connector as you pull back on it. As soon as you get any coolant flow you can close it back up since the air bubble should be sitting in the top of the inverted “U” and the column pressure from the open cooling system should be significant enough to purge any air.


Edit: I should also add that unless you have drained your coolant completely you probably won’t have air in this location. It seems to occur after you have drained and refilled the coolant to the level of the lower hard pipe. This has happened to me twice in the past year: Once when I replaced my t-stat/J plug and again with my second t-belt service. In both instances I lost heat at idle and regained it by “burping” the lower hard pipe/heater return line connection.


Good luck!!

[iceman2k]

Well, after bleeding my system for a few days and ending up with coolant all over my garage, I ended up taking the car back in to the shop for a quick look. We back flushed the heater core over and over and then over again for about 1.5 hours. A lot of hardened pink/white crap came out of my "new" heater core.

We reset all my fault codes and I'm now getting a new fault code for the defrost flap motor after replacing the 3 others. We bled the system again and had tons of heat at increased RPM, but idle was no heat.

After leaving, the heat has been working since at idle and higher RPM. It seems to be working at this point, but, I am not holding my breathe because I have seen this before. The mechanic is leaning towards the heater core being plugged up, especially with all the crap that came out. I'm starting to wonder if the first place I had it at to get the heater core replaced even did it. Maybe they just charged me my left nut and flushed it to get it working. If the heat goes again I will be pulling the old core out and checking to see if it is the original. If it is the original... oh boy!

[fla]

i recently replaced the Coolant flange at the rear of the head, plus a new seal for the Coolant temp sender. Didnt have time to bleed it before taking it on a drive. The water temp went up to 3/4 on the gauge for a ferw seconds and then came back down. Had a load of steam blow out from under teh bonnet whilst stuck in traffic (which scared the crap out of me!) Got to my destination and saw that teh water level was very low. Carefully opened the reservoir cap, water level of course rose up, topped up and then closed the system off. Got back hoime and the level had dropped off again. Topped up again and have yet to take it out for a drive. Do you think there is still some air that needs to be bled out or perhaps a leak? Cant see any drips from the back of the engine, but there is a big water splash on the exhaust manifold now.
Excellent thread Old Guy, many thanks (plus other that have also contributed)

[SlickFix]

A lot of hardened pink/white crap came out of my "new" heater core.

Iceman, how many miles are on your current heater core? Sounds to me like it's time for a new one. Frankly, since the heater core is much more accessible on the B6, I'm surprised more people don't replace it. The B5 folks were always trying to do everything in order to flush the heater core because taking out the dash to replace it was not a very fun proposition. But if I were you, I'd just go ahead and replace the heater core and then see how things are.

[iceman2k]

Iceman, how many miles are on your current heater core? Sounds to me like it's time for a new one. Frankly, since the heater core is much more accessible on the B6, I'm surprised more people don't replace it. The B5 folks were always trying to do everything in order to flush the heater core because taking out the dash to replace it was not a very fun proposition. But if I were you, I'd just go ahead and replace the heater core and then see how things are.

Maybe 15,000km, so less than 10,000 miles on the new heater core. It was replaced January 2011. Since my last flush a week and a half ago, the heat has been working great. Right now I am just crossing my fingers it keeps working. If I need to replace it, then I will do that, but I am shocked a new core would plug up in less than a year.

[markskyline]

Thanks Old Guy! I followed your advice and tried to get all the air pockets out after I had my coolant flushed. The heat is back!

[catamount90]

Am about to attempt almost all of these suggestions this weekend. Thanks very much to Old Guy for the endless advice.

[iceman2k]

My heat still continues to be strong. Some days better than others, but I haven't had cold air yet (knock on wood). Seems like the last back flush and bleed finally has resolved the issue. I just hope it stays!

[iceman2k]

And... it's gone! I think this car has gremlins. Maybe I should start every fall off with a new heater core :)

[A84Harris]

Old Guy, you still around?

[old guy]

Old Guy, you still around?

Yessir. I still stop in occasionally. What can I do for you?

[SlickFix]

*sigh*, I'll just leave this here, again. I keep posting links to this wonder tool in every "no heat" thread I find.

Guys, do yourself a huge favor and spend the $85 for this tool!

[customa4]

Or get it from Advanced Auto. You can get 30% off with code TRT30. It brings the total to about $73 and you only have to spend $2 to get free shipping. Maybe buy an oil drain plug.

[dewey527]

I purchased an Airlift II and works amazing. I have replaced my heater core twice and wasted a lot of coolant and time trying various methods of bleeding without luck through the last couple of years. I hooked it up last night after replacing my coolant flange and it was a snap to replace the coolant without spilling in minutes. You do have to have a compressed air source. Optima Redtop Battery came back from the dead and I have heat with no leaky from coolant flange!

[Europotvin]

Ok so after a couple months of troubleshooting this issue I guess ill try posting here and see if someone can find the issue.

I purchased a 04 A4 1.8t 6spd in Feb last year. Owner told me that water pump was dead and needed to be changed since there was no heat in the cabin. Trying to fix this issue I have changed about every coolant system part on the car:

-Water pump
-Rear coolant flange
-Thermostat
-Jplug
-Heatercore
-Radiator

But even after changing all this, I am still getting almost no heat when temperatures go below 0c. I have blead my system multiple times and dont think I still have enough air in my system to cause an issue (I can open my cap after running my car for a while without my coolant level rising more than an inch). I did not notice any coolant loss since I changed my rad a month ago.

Last thing I did not check is the temp sensors. My temp gauge in my dash seems to work correctly (stops at 90) but it seems that the car heats up pretty quickly (about 5 min of normal driving even at -10deg). Ive also noticed that when I start my car sometimes, my rad fans also starts. Ive tested and it seems to stop when I press the econ. button. So im thinking, is it possible that my HVAC module is faulty and always sending AC or is it possible that my temps sensor is faulty and letting my thermostat open ?

Sorry for the long post, but Im really fed up with this !

[customa4]

Scan the HVAC module for fault codes. The flapper doors that control air flow might not be functioning correctly.

[Europotvin]

Scan the HVAC module for fault codes. The flapper doors that control air flow might not be functioning correctly.

I did scan it and did not get any codes.

[customa4]

Have you pressure tested the coolant system to make sure it's holding pressure?

[BARRY]

Scan the HVAC module for fault codes. The flapper doors that control air flow might not be functioning correctly.

I did scan it and did not get any codes.

did you remove the passenger glove box and watch the servo motors operate when you change temperature as well as vent direction? I did this before I replaced my heater core as safe measure. all colored arms attach to something in the HVAC. going through each function and temp should trigger each to move completely at some point.

[Europotvin]

Have you pressure tested the coolant system to make sure it's holding pressure?

I did not do that yet. It was my next step. At how much pressure should I test my system ?


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[Europotvin]

did you remove the passenger glove box and watch the servo motors operate when you change temperature as well as vent direction? I did this before I replaced my heater core as safe measure. all colored arms attach to something in the HVAC. going through each function and temp should trigger each to move completely at some point.

No I did not check this. Thanks for the tip, ill take a look.


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[Europotvin]

I did not do that yet. It was my next step. At how much pressure should I test my system ?


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So I made myself a pressure tester ans pressurised my system to 13-15psi and did not get any leaks. System kept pressure for over 2 minutes. I really dont know what else to check. I guess I won't have any other choice but to send it to the garage ...

[BARRY]

if the flapper motors are working upon inspection behind glove box then your core is in need of replacement. assuming you've gotten all air out of heater core using bleed hole on the upper hose.

[Europotvin]

if the flapper motors are working upon inspection behind glove box then your core is in need of replacement. assuming you've gotten all air out of heater core using bleed hole on the upper hose.

Ok so I removed my glove box last night and inspected the flapper motors and everything seems to be moving like its supposed to. So since my heater core is new, the only possible problem is that there is still air in my system. Im going to go purchase a vacuum cooling refill kit and try that out then !

[BARRY]

yes you have a lot of air in your system if the flapper doors are all moving. the setup only limits air flow through the heater core, not coolant flow like older cars might have.

[imnuts]

Just looking at the door servo motors and seeing them move doesn't necessarily mean they're moving correctly. The only real way to tell would be to scan with VCDS.

[new_era_inc]

Ok so I removed my glove box last night and inspected the flapper motors and everything seems to be moving like its supposed to. So since my heater core is new, the only possible problem is that there is still air in my system. Im going to go purchase a vacuum cooling refill kit and try that out then !

I replaced my thermostat and flushed my heater core and still no heat. The Only method that worked really well is old guy's method. Cold engine fill slowly and bleed from metal pipe then Heater core return hose. Also lifting the coolant reservoir tank helped push the coolant through. It took me about one week of bleeding it every night. Finally heat is back !!!!!

I also replaced the o ring on my reservoir cap. Just to make sure I covered everything.

Next time I will for sure buy the filling kit.


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