Upper heater core hose has no coolant in it!?!?

[RDA990]

Long story short, I have no heat. It's a PITA because it's winter time and my windows fog up bad in the rain/snow making it close to impossible to drive.

Coolant tank is filled up all the way. I tried to bleed the system through the nut that's on the coolant pipe on top of the intake manifold. No air came out just coolant. I thought that was odd, so I decided to try to bleed the system through the heater core return hose that's behind the firewall. I got the clamp off and spent 15min trying to get the rubber to slide off a bit so I could bleed it through the little hole that's on there. I expected the hose to have coolant in it and this is what I found:







Completely empty and dry. That must be why I have no heat, but what is the actual problem here? Heater core clogged up? Is something else blocking the coolant from getting there? My coolant tank is all the way full. I also blew into the rubber hose and some coolant came out of the metal side.

[omakayd]

Take both hoses off and blow air and/or water through each tube, alternating between the two.
It may take a few minutes with each, just try to watch for clear water coming out the other side each time you do it.
This is what we do at my shop when it's not cost effective to change the heater core and it rarely fails.

Good luck!

[00passat]

Did you unscrew the tank and stand it up so the coolant would be higher than the hose?

[KHARDa4]

Heater core is clogged my friend. It's not hard to change it out the dash doesn't have to be pulled back like a passat.

[Coors]

As mentioned above, remove the lower heater core hose and blow air through the loop, see if anythimg comes out the bottom hose. I bet it's clear, 'unblocked' just air trapped in there.

When you go to fill the system back up remove the coolant expansion tank from its mounting bracket and elevate it as high as it will possibly allow. You want the tank to be higher than the rest of the system. Gravity wil take over from there and force out any trapped air/bubbles in the system. The tank has to be the highest point in the system for the bleed ports to function.

Think about the physics of a beer bong... ;)

Key points to remember while burping the coolant system.
* Never try to bleed a hot engine.
* Only bleed cold engines
* Always open a bleed port (head or HC hose) while filling the elevated tank w/ coolant.
* After coolant begins to spew out of the bleed don't be quick stop right away. Allow a little spillage because you want to be certain you force out all the air. I always allow a pint or so to expel before lowering the expansion tank and capping off the system.

* Then, fire up the engine put the heat on full blast and rev to be about 2k for a minute of two. (Not necessary, but normal practice during my procedures).

[diagnosticator]

The cooling system will fill completely on its own it you allow the time needed for this to happen. It will take about 45 min. Keep topping up the tank as the system fills up. When the level in the tank stops falling, replace the tank cap and run the engine at 2000 RPM until the rad fan runs. Stop the engine and allow the cooling system to cool down then top up the tank as needed. Most problems having air trapped in the cooling system happen because guys get in a hurry refilling the system and don't wait for the coolant to drain down from gravity.

The heater core is plugged in this case however.

[RDA990]

So I did a heater core "flush" on the car.

1. Blew most of the coolant that was in the heater core out with some compressed air.
2. Hooked up the garden hose to one line of the heater core and let the water pass through it for several minutes. Reversed the flow.
3. I let a whole bottle of CLR soak in the heater core for 5-10min.
4. Repeated step 2 for 10min.
5. Used about 5 gallons of distilled water to flush out the remaining garden hose water inside the heater core.
6. Bled the system for a bit.







I got a some "sand" looking deposits out but nothing major out. Heat works great now but sometimes it will stop working and start to blow cold air. On max & hi heat it'll will work for 2 min and then blow cold air for the rest of the time. It's hard to believe the little amount of sand that I got out actually made a difference.

I just bought a OTC Blast-Vac Gun (http://www.amazon.com/gp/aw/d/B000F5ECRW), Prestone Radiator Flush, & a Submersible Pump. Going to use all those things this weekend to try to get the heater core completely clean. I think I didn't let the CLR sit in there for long, so I'll let it sit for about 30min-1hour next time I do it.

[customa4]

For the money you're putting into it I would imagine it would have been cheaper and more effortless to just replace the heater core. It's nice that you're adding tools to the shed but if you go through all of that and your heater core is still screwed then you need to spend the money on a heater core anyways.

[jacobsen]

My friend CLR will not burn out the crust, that crust is mixed with coolant baked to the walls of your core. You need an acid to strip it clean. I did the same thing you did but I started with ZEP drain cleaner and decided to give muriatic acid (hydrochloric acid) a try. It worked like a dream, I let it flow 5-10 minutes in either direction at 50/50 mixed with distilled.
https://www.youtube.com/watch?v=C1Tnu4x8QMg

[RDA990]

For the money you're putting into it I would imagine it would have been cheaper and more effortless to just replace the heater core. It's nice that you're adding tools to the shed but if you go through all of that and your heater core is still screwed then you need to spend the money on a heater core anyways.

I have 2 B6's which have this problem. Buying 2 OEM heater cores for $140 each + the time spent changing them both (Including draining the coolant and potentially making a mess wouldn't) wouldn't be cheaper and effortless to me. All I used was the OTC Blast-Vac Gun which was $50. It worked well, both cars have heat now.

My friend CLR will not burn out the crust, that crust is mixed with coolant baked to the walls of your core. You need an acid to strip it clean. I did the same thing you did but I started with ZEP drain cleaner and decided to give muriatic acid (hydrochloric acid) a try. It worked like a dream, I let it flow 5-10 minutes in either direction at 50/50 mixed with distilled.
https://www.youtube.com/watch?v=C1Tnu4x8QMg

Yea I bet I didn't get it all cleaned out but at least my heat in both cars are working now so I'm not complaining.

[customa4]

Didn't realize you had 2 B6s. Sounds like money well spent if both were experiencing a no heat problem.

[apbro]

Sorry to revive an old thread, but having troubles with same issue. I recently did a timing belt, water pump, and thermostat change. I've read through the replies and tried the following to no avail:
- Elevated front of car about 3'
- Thoroughly flushed heater core with water in upper and lower pipes
- Elevated reservoir

I'm still not getting heat to the interior, and the coolant isn't draining out of the reservoir. Do I need to let the car run for an extended period of time (ie. ~45 minutes) to get things going? Thanks.

[Cybersombosis]

Are you opening the bleed screw? On the 1.8T it’s on the pipe going from front to back under the engine cover. When you flushed the core, did any sediment come out? If done right, you will see white/grey sediment flush out. I change direction 5 or more times until the water going through is clear. I then take compressed air to blow out the tap water then shove the lower hose back on and fill the core with fresh coolant before shoving the upper heater core hose back on.

[lyleswk]

My experience with 2 B6's is that flushing helps, but doesn't solve the problem. You get a little heat if the temps are around freezing, but anything less than that, it's just not enough to change the temp int he cabin on a short drive. Probably going to have to replace the core. And when you do, do a quick inspection. The fins inside the core are very thin and have very little space in between which explains why they clog so often.

[Kevin C]

I have done the slow fill and let the coolant bleed out the pipe above the intake and still got an air locked heater core. What worked for me was to disconnect one hose and block the engine side off and let coolant come out the heater core side. I'm sure it gets harder as the core gets more clogged. I don't seem to remember the car being that fussy when i bought it ten years ago, so it sure seems like an aging clogging heater core issue.

Mine is making random gurgling sounds so I'm swapping it out in the next week or so.

[apbro]

Appreciate the replies. I did open the bleed screw, but nothing happened the first time. Also, when flushing the core there was no sediment or anything like that. I just flushed it from both pipes several times until I got, and maintained, clear water. I went back and re-read:

"Key points to remember while burping the coolant system.
* Never try to bleed a hot engine.
* Only bleed cold engines
* Always open a bleed port (head or HC hose) while filling the elevated tank w/ coolant.
* After coolant begins to spew out of the bleed don't be quick stop right away. Allow a little spillage because you want to be certain you force out all the air. I always allow a pint or so to expel before lowering the expansion tank and capping off the system.

* Then, fire up the engine put the heat on full blast and rev to be about 2k for a minute of two. (Not necessary, but normal practice during my procedures)."

I HAVE HEAT. I guess I wasn't doing things in the correct order or something. But, followed exactly -- Cold engine, opened the bleed screw, elevated the reservoir, and voila, coolant came out of the bleed hole after a few short seconds. Let it drain for a handful of seconds after that till no bubbles. Capped it off. Cap back on the reservoir. And started her up. Got heat basically instantly, even on cold engine.

Appreciate all for their help. Was banging my head against the proverbial wall on this one.

[Puddin Tane]

This tool makes air-free filling so easy it's sick

[Mike Tries]

"Key points to remember while burping the coolant system.
* Never try to bleed a hot engine.

I'm glad you got it working.

Your point reminded me of something... I keep thinking about how badly I screwed up by driving my car onto a race track with the coolant cap off (accidentally). The coolant was boiling, and the head warped. How cool does the engine have to be to safely (for the engine, not our hands) remove the coolant reservoir cap? Is this known/documented? I feel like coolant in the system will flash to steam instantly if the cap is removed on a non-running-but-hot engine. Will that warp a head, or does the engine have to be running for head warpage to follow? Similarly, can we run these engines at all, even from a cold start, with the cap off?

[Puddin Tane]

Until the engine warms up to the coolant's BP, having the cap off is fine, assuming no trapped air. The air does all the expanding below that temp, which could cause local coolant starvation and damage especially inside the head, that being the highest point with the most air pocket potential-- why sloppy coolant fills that leave lots of trapped air can cause damage on their own. That vacuum fill contraption isn't optional IMO. Leaves nothing but small bubbles that purge out immediately when the t-stat opens.

When my reservoir exploded at highway speed it was like a sudden no-cap condition with the engine fully warm. At least half the coolant spewed out of the system within seconds. Pulled over and killed it immediately, no harm done (Coscast AMB head, no less). So I think the answer to this question

if the cap is removed on a non-running-but-hot engine. Will that warp a head?

is NO. The coolant inside the engine will suddenly become steam, as with mine, but that phase change absorbs a huge amount of heat, instantly cooling the cylinders and head enough to prevent damage. The damage happens when the engine keeps running after boil-off; the more tuned the engine and the higher it's revved, the faster the disaster.

[Mike Tries]

Thank you! I think I've been avoiding this coolant cap in ways I don't need to.

[Turbo510]

Until the engine warms up to the coolant's BP, having the cap off is fine, assuming no trapped air.

I agree with that, A story for the readers below.

The coolant inside the engine will suddenly become steam, as with mine, but that phase change absorbs a huge amount of heat, instantly cooling the cylinders and head enough to prevent damage. The damage happens when the engine keeps running after boil-off; the more tuned the engine and the higher it's revved, the faster the disaster.

My experience from holding a radiator hose while releasing pressure is a sudden increase in the temperature of the hose. I'm not clear about the thermodynamics of latent heat, etc., but it is easy to demonstrate this phenomenon.

Years ago, in an Audi 5000, I was not sure if the scenic two-lane highway was the correct way to the main freeway which must be miles away (pre GPS and no map). My wife suggested asking at the motel we were approaching, so as I started to go into their office, some guys walked past and one said "your car is leaking". Expecting condensed water from the AC at worst, I turned to see steaming hot coolant splashing below the engine. Moving the car to the far corner of the lot, expecting a hose clamp or something fairly easy, I could see that the coolant pump seal had blown. I told my wife to see if they had any room in the motel; she comes back telling me that they had one left but "it's $95 a night"! I told her to go sign us up, that we weren't going to sleep in the damn car.

The next day I finally reached my mechanic friend at home, and explained the dilemma. He said "so why didn't you just drive it home"? I re-explained that the coolant was dumping out of the pump's seal vent, to which he said "fill it up with water, leave the reservoir cap off so it doesn't pressurize, and drive it home! I can't believe that you didn't think of that"! "Won't it boil over without the cap?" I asked. "No, not as long as you just cruise at the speed limit". So we walked to the local store, bought jugs of water, and started down the road. First I stopped to check after a mile- water was still right near the filler opening. Then getting braver, went five miles; same thing. I ran the heater just in case, with windows open. A little uncomfortable, being a warm day, but absolutely no problem driving over 100 miles home.

[Puddin Tane]

My experience from holding a radiator hose while releasing pressure is a sudden increase in the temperature of the hose.

Prior to venting and even at its hottest, the hose material is still much cooler than the engine interior. Then when you vent, the liquid coolant in the hose is displaced by super-heated steam that condenses on contact with this cooler hose. Vaporization absorbs heat, condensation releases heat (why steam burns are potentially much worse than scalding by boiling water). So by holding onto the hose while venting you're feeling a latent heat effect the exact inverse of the one happening in the engine.