Luke warm cabin heat & lower radiator hose cold

[GTA]

I don't want to beat this issue to death but I haven't really found any solutions to my problems after hours of searching on this site and others. Hopefully someone here can guide me in the right direction.

Started with just luke-warm heat when the weather got cold. Bought 1 gallon of G12 coolant, lower rad (G62) sensor o-ring and clip from Audi dealer as well as 3 gallons of distilled water.

I removed both lines from heater core and flushed both ports of heater core using garden sprayer nozzle. Removed a little gunk and both sides flowed well so it's not restricted. Followed the coolant flush DYI and drained, flushed with distilled water (twice) and re-filled system with approx 50-50 mix. Bled the system well and found no traces of leaking and my gauge is right where it should be at 90 (12 0'clock).

It was during this process, I noticed that my lower rad hose never gets warm even after running it at 2000RPM for 3 min (according to Shop-Key procedure) AND idling it for over 1/2 hour AND taking it out for spin on the highway and back. The heat seems warmer in the cabin but not much different from before so I decided it was the thermostat.

Bought an OEM stat (Behr) from Audi dealer and replaced it last weekend, bled the system once again but no change (warm heat and lower hose still cold), temp gauge at 90 and no fluctuations. I pulled no codes from VAGCOM pertaining to the cooling system and I also reset the climate control (HVAC, Basic Settings, Group 001, etc) thinking it may be the flaps not positioned properly.

I tested the old stat with boiling water (it didn't open) but I didn't test the new one to see if it was working properly before installation trusting it must be good because it's brand new from Audi. Also, I didn't know the J plug even existed when I bought the stat so I didn't replace it. I assume that if the J Plug failed, I would have a leak but I don't. So should I be worried that it is contributing to my issues? I also didn't know that I can check the water pump impellers when I had the stat out.

The records (receipt) that came with the car when I bought it says that the T-Belt and water pump were changed at 125,000KM (78,000 Miles) in 2008 and it now has 190,000KM (118,000 Miles). The shop specializes in European cars; BMW, Audi, VW, etc. so I would assume it to have the improved version of the WP.

In conclusion,
THE GOOD STUFF:
- No leaks
- No codes, MIL, CEL, nor abnormalities with gauges.
- New OEM stat and proper G12 coolant. Used pressure tester to force coolant into system in addition to proper bleeding of system.
- Expansion tank is pressurizing, gets hot and at correct coolant level.
- Hydrometer (coolant tester) tested for - 30C so it's a good mix.
- Top rad hoses, expansion tank small hose, top hard pipe, heater core inlet hose, lower hard pipe all hot.

THE BAD:
- Only warm cabin heat from vents (livable).
- Heater core return hose warm only.
- Lower rad hose stone cold and and stat housing cold.
- Didn't check the J Plug (didn't know it existed at time of stat replacement).
- Didn't check WP impeller (didn't know I could've at time of WP replacement).

The heat I can live with but I'm afraid coolant isn't flowing properly because of the lower hose issue. Am I being paranoid about this because I never noticed a thing last summer (before I did all this) when it was hot (32C / 90F) and I was driving pretty hard some days. There were no indications of overheating, leaks - nothing.

What am I missing?
- Is the lower hose suppose to be cold because it's cold out? It's about -10C/14F now.
- The only thing I can think of is to check the measuring blocks of the two coolant temp sensors but I don't know the procedures. Maybe that will give me a clue.

Sorry for the long write-up.

[travrach]

No the lower hose should not be cold just becuase it cold out- it may take longer to get hot but it should get warm/hot. Sounds like you have air in the system? Did you bleed it via the hole the heater core hose?

[GTA]

No the lower hose should not be cold just becuase it cold out- it may take longer to get hot but it should get warm/hot. Sounds like you have air in the system? Did you bleed it via the hole the heater core hose?

Not sure if there was a hole in the heater core hose but I did bleed it with the screw on the top hard pipe at the top of the engine near intake manifold. No air - all coolant from this screw. Can you tell me exactly where this hole is you're referring to?

[travrach]

This hole is higher then the screw, better to use hose hole. Pull off the plastic cowl where the battery is, complete thing. The hose has a white dot on it I think, you will see a small hole in the hose, remove the clamp and pull hose back so hole is exposed(no longer touching core tube) but some of hose remains on the tube. Start car and wait for coolant to pee out, this may even take a few times of running it.

[Timtheguru]

I'm just going to regurgitate this again. Try changing the coolant expansion tank cap. It's what holds pressure on the coolant system.

[GTA]

Travrach: From what I can tell, you're saying one of the heater core pipes has a hole in it that is higher than the hard pipe bleed screw that I can use to bleed the system? If that's the case, I'm thinking I should I jack up the rear end of the car to make that hole even higher to get rid of any air pockets once and for all. Does this make sense?

Timetheguru: The expansion tank pressurizes fine and acts like it's supposed to. Any reason why that is related to my issues of lower rad hose not heating up and just warm heat in cabin? Just curious because I'm on my witt's end at this point.

[Timtheguru]

$3 cap and will solve your problem probably. How do you know that the cap you have now is pressurizing correctly? Pressure testers are in place of the cap so there is no test for the cap.

With correct pressure it will bleed out any air in the heater core since the system is self bleeding, without proper pressure applied air bubbles can re-appear in the system.

Not the $3 part... but can be had for that amount.

http://www.ecstuning.com/Audi-B6_A4-...Tank/ES253082/

"Keep proper pressure on your coolant
The coolant expansion tank cap maintains an elevated cooling system pressure to raise the boiling point of the liquid coolant, while venting excessive pressure to atmosphere. These caps have a limited service life; they should be pressure-tested as part of a routine maintenance schedule, and replaced as part of any major cooling system overhaul.
This bright blue cap includes a replacement o-ring, and dresses up the appearance of any engine bay."

[GTA]

Thanks for your input guys. You guys convinced me that there may still be air in the system. I'll try your suggestions this weekend to bleed the system again using the hole technique as well as getting an OEM pressure cap from the dealer. Why the F__ is bleeding this system so hard? I've been working on cars most of my life, including older VW's (this is my first premium German brand) and have never had anything so simple become so complicated. Arghh!

[Timtheguru]

Before you try to bleed through the little hole on the heater core hose, put the new cap in and drive around for 20 miles or something like that. The system is supposed to be self bleeding with the expansion tank.

[GTA]

Before you try to bleed through the little hole on the heater core hose, put the new cap in and drive around for 20 miles or something like that. The system is supposed to be self bleeding with the expansion tank.

Good suggestion Tim. Should I just drive normal or like a maniac to get the revs up? Would a run on the highway doing around 60MPH @ 3000RPM good enough?
BTW, this is the first time I've even heard that this system is self bleeding. Kinda makes sense as most the cooling system issues I've read so far has at least something to do with the bleeding of this system.

Cheers dude!

[Timtheguru]

I wouldn't drive like a maniac, but just put some normal driving on, maybe even go more than 20 miles. Then check the level of the coolant.

[travrach]

OP, you can see the hose here

Are the hoses hard with car running after few minutes? If so; its holding pressure. You can idle a car with no cap and still have heat..just FYI.
Yes these system are very tricky to bleed out after you work on them.

[Charles.waite]

You might also consider that the water pump might be broken. It could very well be a possibility...

[A4avanttt]

I am having A similar problem. Flushed the system and heat came back for about 1 week then went back to cold. Only gets warm at freeway speed. Could heater core be blocked again even after I flushed with garden hose? I am going to try all suggested procedures. I have a new baby and having no heat during winter is a pain in the butt. Thank god for the heated seats.

[GTA]

OK. I've replaced the expansion tank cap (CAD$37.00) and drove around on Saturday but made no significant difference in cabin heat and my lower rad hose is still cold. At least I got a new cap that I can rely on. So I spent a couple of hours the next day at my friend's garage to bleed the upper heater core hose through that hole.

After driving down there, the car was at operating temp. Immediately and while the car was still hot, I followed this simple tip (listening to gurgling as sign of air pocket) from 'old guy' here:
http://www.audizine.com/forum/showth...=1#post5913397

Sure enough, I heard gurgling along the top hard pipe and the same time the level of the tank rose over an inch which confirms a (not so) nice air pocket. In addition to this, the bottom hose of the heater core was hot and felt pressurized but the top hose was just warm and felt hollow (not pressurized). This doubly confirms an air pocket in my heater core and makes sense because it is indeed the highest point in the cooling system (if even by a couple of mm).



Since I had recently flushed out my heater core, it was very easy to remove the upper hose to bleed it. I slid the clamp off the hose towards the firewall and slowly pulled back the hose to expose the hole over the end of the upper pipe leaving about 3/4" hose on the pipe. Initially nothing came out of the hole so there was definitely air in there. I removed the exp tank with cap on tight and raised it up as much as I could.

After a couple minutes of idling, coolant started to squirt out of the hole. From here, I pushed the hose back in enough to cover the hole and left it for a minute to let the air accumulate again, then slowly pulled it again to release more air and squirts of coolant. At this point, the upper hose got hot (be careful!). I repeated this 4 times without shutting off the car. For insurance, I had a friend rev it up to 2000RPM to bleed it a final time, put the hose back and clamped it down.


Now I have much better heat and my lower rad hose is now warm (AT LAST!!!).

Is my problem resolved for good? Only time will tell and since the ambient temps have gone above freezing, I will have to wait for some colder weather to determine that. Regardless of my outcome, the tips and tricks I have discovered on this site are well founded and accurate.

Thanks to all those who contributed and I will give it some time to make a definitive statement just because I didn't know about the J Plug when I replaced the thermostat, and it may yet bite me in the A$$ and introduce air into the system. If it does, I know exactly what to do :-))

I have pics of what I did but can't figure out a way to post it because I don't have any external places to upload to in order to link it.

** UPDATED with Pics **

[SlickFix]

I have pics but of what I did but can't figure out a way to post it because I don't have any external places to upload to in order to link it.

photobucket.com works pretty well as a photo hosting site. It's free. There are also many others, too. Just do a google search for "photo hosting".

[Timtheguru]

I really like picasaweb.com (goggle's servie). Keeps prying eyes out of your albums with no link pics.

[travrach]

Nice job OP, and very good idea to do multiple bleeds! I'm sure some cold will be on it's way soon.

[GTA]

OK. It was cold last week and the issues came back. Bought a J Plug (Audi calls it a Banana Plug), a gallon of coolant and a gallon of distilled water. I looked for a way to replace the J Plug without removing the newly installed thermostat but couldn't so I did the whole stat replacement procedure again and bled the system. I did find out my water pump has a metal impeller and it was intact.

Had heat and lower rad hose warm on the way home but this failed once again a day after. Now I'm really at my wit's end. Gotta be another leak somewhere!

Frustrated and totally confused, I spent the morning yesterday at the garage and did another pressure test of the system (@ 20PSI). But this time, I combed through every aspect of my cooling system to eventually find that the lower heater core hose had a small pin hole in it about an inch from the end. S.O.B!!! Since there was coolant all over the place the last time I bled it, I was virtually invisible to me.

I removed it, cut off the bad piece and it was long enough to go back in without much strain on the hose. I read somewhere that someone else had the same problem. So was this a coincidence? Or a defect? Since I can't definitively answer that, I will do an update if this stabilizes my issues. Stay tuned...

[GTA]

So far, so good. I have relatively good heat in the cabin, not scorching like my previous VW's, but good enough. I guess that's about as good as it gets. At the same time, I am more confident in my cooling system after replacing the t-stat, J-plug, coolant, etc. and confirming that my water pump has a metal impeller.

Nice work to everyone that have contributed to this thread. Cheers!!!

[DurtyD]

When you bled the system did you jack the rear of the car up slightly like you mentioned?

Also, what are you referring to when you say J-plug?

I too am having the same issue.... lower rad hose is cold, top of my engine seems pretty hot but guage reads 90... Wondering if the coolant sensor is gone and that maybe the gauge is lying to me?



...also, I aplogogize for bringing up an old post.

[Collinscj]

My problem was heater core, look at how gunked up it was when I pulled it. The holes are from when I stuck a knife inside to try as see what was going in there. I tried bleeding it numerous times with no luck. The heater core is sooo easy to change out surprisingly. It only took me 25 minutes to swap the two. Honestly it's worth just buying a $70 heater core at ECS and swap em out. Easy fix to your no heat.

[OMG_SHARK]

When you bled the system did you jack the rear of the car up slightly like you mentioned?

No need to jack up the rear. Just remove the clamp(not a one time use clamp so you can reuse it) and expose the hole on the hose.

[DurtyD]

Listening to the car running while putting my ear close to the grille, I hear hissing sounds, Like water droplets hitting hot metal surfaces.... this must be the gurgling sound Ive read about on these forums. Leading me to believe there IS air in the system...

Could it have gotten in from the heater core itsself? Looking at those pictures Im sure its possible for them to go and this car has 210,000 on it but I get heat and AC, its just mild temperatures like the OP mentioned....

[GTA]

DurtyD:
No sweat on the old post. Glad to offer my experiences. I didn't jack up the rear of the car when I bled the system. I figure that there's no need to and you shouldn't have to bother yourself with that.

The "J" plug is a plastic expansion plug located next to the thermostat and if you take it out, it actually looks like the letter "j"; hence the J-plug. The Audi parts guy called it something else but everyone on these forums call it a J plug, so there you are. It's a cheap enough part though and is held in with one bolt to the engine block. It's relatively easy to remove and replace but be prepared to top up with OEM coolant/water if you do.

As for your temp guage, I considered the same thing you are but since it seems to operate normally so I didn't fault my guage or temp sensors. Since I did all that work near the end of last winter, I have yet to really test it in a frigid environment. Suspecting the temp mixture flap now because the outer vents (at ends of dash near side windows) get hotter (and colder with AC) than the center vents.

If you smell coolant inside the car, then it may be your heater core. That's the first sign of heater core leak. That hissing sound near the grill may indicate a leak somewhere in the radiator area, not the heater core. I would suggest you do a pressure test to try to find if you actually have a leak. But be careful not to put too much pressure in the system because you can blow something. Not exactly sure the spec but 25 PSI should be the limit.

Hope this helps you out.

[GTA]

UPDATE: WP was leaking and dripping on to my crank pulley. Previous idiot siliconed the WP to the block because the rubber O-ring was flattened out and hard as a rock, I suspect. I needed to do the TB anyways as it was nearly 100K Km since the last TB change (according to the records from the previous owner).

Replaced WP and TB with full HEPU kit:

http://www.audizine.com/forum/showth...as-anyone-used


Heat seems to be better but haven't had too much time with the change yet. May have to burp it again because these cooling systems are funky to the core. Still smell a little coolant after a shutting down but not as intense as before the TB/WP change.

[seanf86]

if you keep getting intermittant heat replace the heater core, after flushing and flushing the damn thing I gave in and bought one and replaced it, I now have tons and tons of heat. I got an all alum Spectra Premium from rockauto and it came with the clamps and seals for like $77 CAD. It is made in China but I've had good luck with other spectra stuff I've bought in the past, if it shits on me...well theyre easy enough to change that I won't be that upset.

[GTA]

Hmmm. I may try that if this issue gets longer in the tooth. That still doesn't explain my coolant smell from under the hood though. I never smell it in the cabin at all.

I'll keep that part in mind as it's cheap enough. But I'm not sure about the easiness of the job because I've never look that up, though I'll take your word for it Sean.

3 years with little to no issues and all of a sudden, I've done the TB/WP, RF bearing, RF axle seal w/ new OE trans fluids, welded pinholes in resonator, front brakes (though this is maintenance). I'm just glad I'm able to do this stuff myself, though frustratingly so. Still around $1k in parts alone for the above.

Next task before winter is flushing out my brake fluid and bedding in my new front brakes (Zimmerman rotors, TRW pads) but gotta find a good place to do it. Since last weekend when I replaced them, I've been gingerly braking like I'm stepping on an egg and looking far ahead to anticipate my stops . I may get up this Sunday at 4am to do it on the nearest expressway.

[seanf86]

Hmmm. I may try that if this issue gets longer in the tooth. That still doesn't explain my coolant smell from under the hood though. I never smell it in the cabin at all.

I had that problem as well, check out the rear coolant flange, I used to get a phantom coolant smell in my garage when I'd walk around the front of the car after shutting it off, turns out my coolant flange was leaking just enough to make a smell.

[GTA]

Yes, it is a phantom odour. Nicely put. I'd considered that and know they do leak due to the flange material and O-rings aging but it was replaced before (according to an old invoice I have).

Was yours leaking just enough for the smell but leaving no dried up liquid traces? I changed the CTS back there a while ago and found it to be a PITA as I didn't remove the plumbing around it. Maybe it's time to do that for peace of mind. Was it a PITA for you to do?

[seanf86]

Yes, it is a phantom odour. Nicely put. I'd considered that and know they do leak due to the flange material and O-rings aging but it was replaced before (according to an old invoice I have).

Was yours leaking just enough for the smell but leaving no dried up liquid traces? I changed the CTS back there a while ago and found it to be a PITA as I didn't remove the plumbing around it. Maybe it's time to do that for peace of mind. Was it a PITA for you to do?

it was a bit of a pain in the ass, the one on the car was only a few years old but it was not a genuine piece, I had it done in about an hour or so but cut my hands up pretty bad, to top it all off my wifes B6 the flange went a few weeks later and had to change that one so I can do them pretty quick now.