No Heat - Air leak or clogged heater core???

[gimmemoedmb]

I've searched and searched and bled and bled and I can't get constant heat in my '03 A4 1.8T. First off, my temp gauge works perfect. It slowly heats up and stays at dead center constantly. I've opened the reservoir cap and it bubbles and I can hear air in the coolant. At idle the air is cool but when I rev the engine it gets warm. The top heater core hose is cool while the bottom is hot. There is either air trapped or the heater core is blocked. I have bled the coolant for hours and pulled the top core hose off several times and filled it directly with coolant.

Last night I hooked up the shop vac and sucked 3 gallons of water through the heater core and not one particle of dirt or debris came out of the heater core came out so I don't think it's clogged. However, how restrictive should the heater core be? I poured water into a clear hose about 18 inches above the top heater core line and let it drain out the bottom (both hoses to the engine were disconnected) and a slow steady stream of water came out. I expected the water to run right through the core but it was rather slow. Is this normal?

I believe I got most of the air out of the system last night and the heat was pretty warm. When I rev'd the engine it actually got hot so I thought I had it and I just needed to bleed a little more air out. This morning I started it, let it warm up, and it's cold again. When I started it I could hear coolant sloshing in the heater core which makes me think I have an air leak. I do think it would have to be a fairly large leak because it sounds like a lot of air in the system. I changed my oil a couple weeks ago and the oil looked fine, I didn't see any coolant in it. I don't see any coolant leaking onto the garage floor, however it's difficult to tell with all of the snow we have here in MN because the car is covered in snow so it melts all over the garage floor, making it more difficult to tell if there's coolant. I'm leaning towards a leaky j-plug but would that allow that much air into the system? Sorry for the long rambling, I think I covered everything but I'm sure I left something out. I've spent 8 hours messing with this and many more hours reading on here and I just can't spend a lot more time on it.

[CyberPMG]

You probably still have an air bubble. There's a good thread in here that explains the best way to get rid of it. If you had a large leak, you would notice the level in the reservoir tank drop.

[gimmemoedmb]

I have read that whole thread several times and tried every technique. I swear I had all of the air out of there but it's possible I didn't. I did notice the coolant was a little low last week and I topped it off. It's hard to say if I've lost any coolant the last few days because I've been bleeding and pulling hoses and losing coolant and topping off. Thanks for the input.

[widgget]

i've got this exact problem with my 5spd.

the guy i bought it to for the coolant sensor topped it off with some "mix with any color" coolant and i don't trust it so i haven't looked to far into this aside from a from quick beading since i will be flushing it in the next week anyway. going to be so pissed if it's all jellied up.

keep us updated, will try to do the same.

[Haenszel20v]

What did you change to make this happen? did it happen on its own? If so, I'm leaning towards water pump.

[gimmemoedmb]

I believe it happened on it's own. We've only owned it for a couple months but a month ago it blew crazy hot heat, I was constantly having to turn it down because I would get too hot. My girlfriend then noticed one day it started getting cooler. It's her car so I don't drive it everyday but I do drive it a few times a week.

[gimmemoedmb]

Should my heater core flow freely? When I pull both hoses and connect a 12" clear tube with a funnel to the core outlet and pour water in, it comes out the inlet in a steady stream but it is slow. I can easily fill the funnel up and then I have to wait 15-20 seconds or so for the water to flow all the way through.

[Trev]

With the car at operating temp (and coolant system pressurized), pull back on the heater core outlet hose (there's a small pin hole on the top just before the end). Do you get air or a steady stream of coolant?

[gimmemoedmb]

Most of the time it's air, but I've bled that several times as well until I get a steady stream. Then I go back later and it's all air again.

[42no_B6]

Having the same problem here. Been ongoing issue for me for about a month now....

[gimmemoedmb]

Update: Last night I bled basically only through the heater core upper hose bleed hole. I opened the hole and rev'd the engine until coolant came out of the hole. Then closed it. Then rev'd the engine for awhile and then opened the hose bleed hole and a bunch of air came out. I did this until all coolant came out. I repeated this process for 30-40 minutes and I had pretty good heat. I let the car cool for a couple hours and repeated the whole thing over again. By the end my heat was quite warm and when I would rev the engine to 2-3k it was actually hot.

After letting the car sit for an hour I went back to check on it and I could hear a small hissing that sounded like it was coming from the coolant reservoir. Is this normal or could this potentially be my air leak? I didn't think a leak at the reservoir would get air into the system, just more air in the reservoir.

This morning the heat was just slightly warm at idle and got warmer as I drove it but it's no where near where it was last night.

[42no_B6]

Did the same thing, only difference is mine started an overheating issue when driving. I've heard a hissing noise also from the resevoir but thought its just the resevoir allowing for expansion. I've had both the resevoir and cap replaced so I doubt its those...

[diagnosticator]

I have never heard of a b6 heater core clogging. a no heat situation is almost always due to an air lock or bad coolant pump. If after bleeding the system, there is always air afterwards, then there is a coolant leak or a bad head gasket. To determine where the leak is, a pressure test is required, both hot and cold system.

[diagnosticator]

Did the same thing, only difference is mine started an overheating issue when driving. I've heard a hissing noise also from the resevoir but thought its just the resevoir allowing for expansion. I've had both the resevoir and cap replaced so I doubt its those...

If your A4 is overheating with the cooling system full, then it is likely the coolant pump is bad. If the system expansion tank is empty, then the overheating is likely due to coolant lost due to a leak. Or, the lost coolant is overflowing the tank cap due to over pressure from overheating,

[Phoebusvh]

I have no heat for the last few days. Bled system and there was air coming out. The wierd thing is the center vent by the windshield always give heat, other vents give cold air. So when I switched to Circulate air within the car, (not the Auto Cir) with Econ on, all vents were giving warm air. I still have no idea what to do to completely fix this problem.

[diagnosticator]

I have no heat for the last few days. Bled system and there was air coming out. The wierd thing is the center vent by the windshield always give heat, other vents give cold air. So when I switched to Circulate air within the car, (not the Auto Cir) with Econ on, all vents were giving warm air. I still have no idea what to do to completely fix this problem.

In the case where some of the vents have hot air and other don't, is caused by the air flaps getting stuck or not responding to the controller in the heater housing. You can try resetting the basic settings of the HVAC controller using VAG-COM.

[gimmemoedmb]

I have never heard of a b6 heater core clogging. a no heat situation is almost always due to an air lock or bad coolant pump. If after bleeding the system, there is always air afterwards, then there is a coolant leak or a bad head gasket. To determine where the leak is, a pressure test is required, both hot and cold system.

Thanks for the comment about the heater core. I didn't think this was the issue but was surprised that coolant didn't flow through it more freely. I'm almost positive I have an air leak. I am going to do a pressure test tonight or tomorrow to hopefully find it.

[42no_B6]

If your A4 is overheating with the cooling system full, then it is likely the coolant pump is bad. If the system expansion tank is empty, then the overheating is likely due to coolant lost due to a leak. Or, the lost coolant is overflowing the tank cap due to over pressure from overheating,

Waterpump was changed over summer with metal impellar. Expansion tank never gets empty. Thats the confusing part, so there's no loss of coolant. I'd like to pressure test but can't find an adapter for my cooling system pressure tester, anyone know a site?

[gimmemoedmb]

Yeah, I just ran to a couple different auto stores looking for a cooling system pressure tester. They both had them but no adapters for an Audi. One of the places had like 16 different adapters and none of them worked. I'm debating about just replacing the j-plug this weekend because I'm thinking that's the most likely culprit. I cannot see a visible coolant leak anywhere so I'm guessing it's sucking in air when it cools. I've changed the oil since I've lost heat and there was no coolant in the oil. My coolant also doesn't have any oil in it. I'm thinking for the $10 part and some time in the garage I may as well do it.

[O2VW1.8T]

It took me a long time to get the air out, i tried pulling a vacuum and that didnt work. So i flused the core with a hose for 20 min. Then blew all the water out, filled the heater core first with coolant to make sure no air, hooked up the lines and that it. Didn't even have to bleed the system it was hot in minutes and its been 2 weeks and still blowing hot..

[42no_B6]

Seems like some people get the flush easy, while the rest of us been having a crappy time. I'm thinking the same thing with the j plug. I visually checked mine out and didn't see a leak, but its the only other part that plastic that I could think of would expand when heated, then retract when cooled, letting air in. The only other thing I was thinking was to place silicone sealant around it as a way to check

[Phoebusvh]

Guys, check out the temperature sensor, there is one right behind the engine (based on what my friend told me). His car was a convertible A4 and last year he got no heat with no sign of leaking of any kind. He flushed the system then replaced the temperature sensor and everything works ago. He also said the engine temperature needle still works perfectly fine back then.

[diagnosticator]

Waterpump was changed over summer with metal impellar. Expansion tank never gets empty. Thats the confusing part, so there's no loss of coolant. I'd like to pressure test but can't find an adapter for my cooling system pressure tester, anyone know a site?

http://www.samstagsales.com/vwaudi.htm#cooling

[gimmemoedmb]

This morning I stopped by an Advance Auto and they happened to have the Audi adapter with their pressure tester. I tested it in the parking lot and it turned out my lower heater core hose had a leak in it. When it was under pressure a steady stream was shooting out of the hose. Leak found! Luckily the hole was right at the end of the heater core nipple so I was able to just cut an inch off the hose and didn't have to replace it. I'm really glad I was able to find that so I didn't spend the afternoon replacing the j-plug for nothing. My heat is quite warm, not hot yet, so I will bleed it some more over the next few days but I think my problem is solved. Thanks to all for the help and good luck 42no_b6!

[42no_B6]

Man that's awesome to hear. I was about to lose all hope but in the process of getting my adapter, I'm just hoping now its something as easy as that!

[jacksonjames]

Idle my car gets cool, driving it's fine... it's been like this for 3 years, and i have never thought to fix it because we don't sit still for long.

yesterday, i started it before i was leaving and let it idle for about 10 minutes.. idled fine... when i got in it to leave, it started sputtering like it was running out of fuel. sitting idling it seemed to be fine, but under load it would sputter and wanna die. i looked and noticed the temp gauge was moving up and down, went to the middle, then back down, then back up... never past the middle though.. so i don't think it was overheating.

finally it just stopped running all together and is turning over, almost starts, but not quite.. i know that i'm all over the place with this, but any thoughts on what it may be.. my wallet is shaking with fear right now..

none of the check engine lights came on, so i'm wondering if it's fuel related...

does any of this make sense? :)

oh btw, i have a 2004 a4 1.8t quattro

[gimmemoedmb]

So it turns out my problem is not fixed. I still don't have heat. I'm starting to lean towards a clogged heater core. What kind of flow rate should I have through the core? Mine is definitely somewhat restricted but is that normal or should it flow as fast as I can pour water in? It took a few minutes to suck about 3 gallons of water through it with a shop vac. It seems slow but not one dirt particle came out, it was all clear water.

There's possibly still some air in there but I have bled the sh** out of it. Today I even drained the coolant from the temp sensor and refilled. I have a steady stream out of the hard pipe bleed screw and I get a steady stream out of the heater core bleeder hose but still almost no heat.

I've also thought it could be the head gasket however there is no oil in the coolant or coolant in the oil. The coolant does not have any exhaust smell to it and the exhaust does not have any coolant smell to it. I pressure test the coolant and it holds pressure at 15 psi. I did a compression test (cold) on the cylinders today and got 180, 160, 172, 179. I added a cap full of oil to the 160 cylinder and got 180.

I'm going to try a little more bleeding tomorrow and maybe try flushing the core again but otherwise I'm stumped.

[gimmemoedmb]

I know it's late, but I wanted to follow up because I hate when threads don't have a final solution. I did end up fixing my no heat problem. It was indeed a clogged heater core. So here's a summary of my solution to hopefully help someone out in the future.

My no heat problem started back in November. I knew there was air in the system but couldn't figure out where it was coming from. I ended up finding a coolant pressure tester with the Audi adapter at Advance Auto after going to two other stores. I immediately found a large leak in the hose to my heater core. Luckily the hole was right at the end of the hose and there was enough slack so all I had to do was cut off an inch of the hose and it was fixed. I bled the air out and briefly had heat but it soon went away. After tons of bleeding air and trouble shooting I ended up flushing the heater core. I first used drano, flushed with water, and then let clr sit in it for 15-20 minutes and flushed with water again. I did this two separate times. No big clogs came out but there were many very small pieces that I could see in my clear hose. I then did a final flush using a shop vac and sucked maybe 15-20 gallons of tap water to make sure I got all of the clr and drano out. I then flushed with distilled water. Finally I buttoned everything up and bled all of the air out, using both the bleed screw on the hard pipe and the bleed hole on the top heater hose. I found it easiest to do this when the car was cold. I simply unhooked the coolant tank and lifted it up until coolant came out of the bleed holes (one at a time). I did this a few times after letting the car get up to temp and cool down. I have now had hot heat for over a month. Hot enough that I am sweating in the car when it's 0 degrees outside. I still feel like the heat isn't quite as hot as it originally was so I think it may still be slightly clogged but the heat has been more than adequate. I may flush it again this summer or maybe even just replace the heater core. I hope this helps and thanks to everyone for their input.

[A4SoftWalker]

HAHAAA good to know u finally got ur sweat on.

So, what caused the initial clogging? Are u guessing improper coolant type that caused clumping to gunk up your flow?

[Silver A4]

In case anyone was looking for an easier or cleaner way to burp the heater core, I found a way that worked really well. Get a turkey injector and add coolant through the coolant bleed hole. It takes a little while but you will be able to fill the hose and the core completely and without a mess. My heat is just as hot as it was when the car was new. You can use the needle but I would suggest tapeing the second hole at the top of the injector and cut the tape don't pull it to rip the tape because you'll break the needle. Also don't poke a hole through the bottom of the hose. If you don't trust yourself with the needle take it off and just use the tip of the injector. You can use the overflow tank to add coolant, just fill the tank when your done.

[dirtybrd]

I have never heard of a b6 heater core clogging. a no heat situation is almost always due to an air lock or bad coolant pump. If after bleeding the system, there is always air afterwards, then there is a coolant leak or a bad head gasket. To determine where the leak is, a pressure test is required, both hot and cold system.

Mine did, not idea how. Had to blow it out with my water hose and a fire hose style nozzle!