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Discussion Starter · #1 ·
Question for all the folks who have done heater core flushes..

My 2005 Passat with 118k miles has never had a heater core flush, as far as I can tell. The coolant has been changed I would say 3x.

Here is a picture of the heater core nipples coming through the firewall.

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Given how folks have said if the nipples are brown, they are probably brittle, at least from the outside, mine look pretty good. Am I correct to say the the part inside the heater core hoses (currently not visible) may be in bad shape, or does the pic give me a glimmer of hope that they are still in good shape, ie. Not brittle?
 

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They may be aluminum, which is good, but if they are plastic they are at least fragile. In either case, take care when removing the hoses and doing the flushing and you should be OK.

Be very careful prying off the existing hoses since that is usually where damage occurs. Either use a pick to release the hose from the nipple before pulling it back or use hose pliers. In either case, twist the hoses while pulling back and try to not squeeze the nipples inside.
 

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If the 3 coolant changes were done at around 40k mile intervals, and has been consistently changed/flushed and replenish with g12 or g13 coolant, I would think a heater core flush would be unnecessary. Especially if you are experiencing good heat from the vents.
But if you want to do it for peace of mind, that would be fine too.
 

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I have no heat. So I'll have to flush...
FWIW my 2002 Pwagon had the classic no-heat condition and I did the heater core flush each winter for a few years. Flushing may help but I found it only restored about 20-30% of the full heat and did not last for an entire VT winter (Dec-March). Rule out it is not your controls and find a friend or two to help remove the dash so you can replace the core. It will make all the difference! The dash job is not as bad as it looks but it is not a one person job. If you look at the videos you will see the best method is the one where you disconnect the steering U-joint and essentially lift the entire dash assembly back away from the firewall. I needed two extra sets of hands for mine, the dash+steering assembly is really heavy and it works best to have a person on each end holding it while you swap out the old core.
 

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I have a 2001.5 Passat GLX 4-motion that has had a temperamental heater core over the years. I end up attaching clear tubing to both of the heater core hose connections and clean out with CLR. Put the CLR into the core, let it sit for 15-20 minutes, then flush it back out. Flushing entails filling the loop with water then using light air pressure to move the crap out. I use a paint strainer to filter out all of the solids afterward and there is always a substantial amount of crap being separated out. I flush in both directions to get everything out. Be sure to do the flushing process multiple times to thoroughly get the CLR out of there. I have to flush like this heater core every couple of years. Once flushed, the heat is fine. Also be sure to purge the air out of the core once you put the system back together and fill it with coolant. That heater hose on the left in the photo with the little hole in it is just for that. That hose is the return. If you squeeze and move the clamp back enough, you can pull the hose back and most of the air will bubble out that little hole until there is only solid radiator fluid coming out. Just be careful because the system is under pressure once it gets up to running temperature.
 

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Question for all the folks who have done heater core flushes..

My 2005 Passat with 118k miles has never had a heater core flush, as far as I can tell. The coolant has been changed I would say 3x.

Here is a picture of the heater core nipples coming through the firewall.

View attachment 106155

Given how folks have said if the nipples are brown, they are probably brittle, at least from the outside, mine look pretty good. Am I correct to say the the part inside the heater core hoses (currently not visible) may be in bad shape, or does the pic give me a glimmer of hope that they are still in good shape, ie. Not brittle?
Are you sure it is the heater core and not the blend door actuator (depending on the model)?

337k miles on my ‘98 and never needed a flush. Good maintenance made sure of that. The plastic tubes broke but just pushed the hoses further on up the tubes closer to the firewall.

On my ‘05 that was purchased used, that car had multiple heater issues. Not only was the heater core plugged but the blend door actuator didn’t work. To make things worse, the previous owners mixed the pink antifreeze with green and it turned kind of gummy.

Before messing with the core, check the temperature of the hoses in and out and that they are roughly the same temperature. If one is noticeably cooler than the other then yes, it is a heater core problem. That was the case on my car and backflushed the heater core with great success. Be gentle, the pressure in the cooling system is less than 20psI. I used a Blast-Vac. Flush opposite the normal direction of the flow otherwise you will probably force the debris deeper into the heater core. I put a hose onto the heater core to direct the waste during the backflush into a bucket and not all over the engine. An unbelievable amount of ’stuff’ came out of the core.

Do not use any chemicals to flush the heater core. You run the risk of ruining and necessitating replacement.

Fortunately I had the wherewithal to bypass the heater core when I did a chemical flush of the engine. Some of the coolant pathways and the engine block drain were plugged due to the old antifreeze slurry. Within a minute after introducing the flush solution the radiator sprung leaks everywhere. Guess what? Mo’ Money!

I had planned to replace the thermostat after the flush as well. Which in turn then needed to replace the thermostat housing because it was quite brittle.

One year later I have no heat again. I bought an aftermarket blend door actuator. Sigh.

If you have a Climatronic there is a self diagnostic test mode.
 

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Are you sure it is the heater core and not the blend door actuator (depending on the model)?

337k miles on my ‘98 and never needed a flush. Good maintenance made sure of that. The plastic tubes broke but just pushed the hoses further on up the tubes closer to the firewall.

On my ‘05 that was purchased used, that car had multiple heater issues. Not only was the heater core plugged but the blend door actuator didn’t work. To make things worse, the previous owners mixed the pink antifreeze with green and it turned kind of gummy.

Before messing with the core, check the temperature of the hoses in and out and that they are roughly the same temperature. If one is noticeably cooler than the other then yes, it is a heater core problem. That was the case on my car and backflushed the heater core with great success. Be gentle, the pressure in the cooling system is less than 20psI. I used a Blast-Vac. Flush opposite the normal direction of the flow otherwise you will probably force the debris deeper into the heater core. I put a hose onto the heater core to direct the waste during the backflush into a bucket and not all over the engine. An unbelievable amount of ’stuff’ came out of the core.

Do not use any chemicals to flush the heater core. You run the risk of ruining and necessitating replacement.

Fortunately I had the wherewithal to bypass the heater core when I did a chemical flush of the engine. Some of the coolant pathways and the engine block drain were plugged due to the old antifreeze slurry. Within a minute after introducing the flush solution the radiator sprung leaks everywhere. Guess what? Mo’ Money!

I had planned to replace the thermostat after the flush as well. Which in turn then needed to replace the thermostat housing because it was quite brittle.

One year later I have no heat again. I bought an aftermarket blend door actuator. Sigh.

If you have a Climatronic there is a self diagnostic test mode.

Additionally - Very Important! Properly and correctly bleed the cooling system! A blown head gasket might be the result if air is left in the system.
 

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Discussion Starter · #13 ·
Thanks everyone so far for the replies. I read the internal memory of the Climatronic, and it had no errors present, ie. it displayed 444 on the left and 00 on the right.

I assume that there is no need to run any diagnostics?
 

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Folks, quick question. If there is air in the heater core, can I raise the coolant tank, making it the highest point in the cooling system to remove the air from the core?
 

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You could but the heater hoses go downward to the back of the engine where the coolant hard pipe is so it won't help you out with the air in the heater core.
The thing to do is slide back the (passengers side) heater hose to allow the air to escape through the bleed hole.

Slide the bleed hole (red arrow) to the yellow line and let the air bleed out.

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Discussion Starter · #18 ·
@Urlik, thanks for that link. That correlates to other posts I've seen. I guess I'll have to move the hose as @AndreasPassat mentioned. I'm just worried about disconnecting the hose given the car's age.

Reason I'm asking is I started to get heat in my car, as in really good heat yesterday.

Now I'm starting to wonder if my heater core is fine and there was just air in the core. Reason I thinking this is the following:

1) A couple years ago, probably 2 years, the dealer said that my coolant reservoir needed to be replaced. I agreed and they changed the reservoir.
2) Three (3) years ago when my daughter was driving the car to school, she said the heat was working fine. I drove the car too and would have noticed if the heat wasn't working.
3) About 4 weeks ago I had the TB, water pump, thermostat changed.
4) Ever since the change, I've noticed that I'm getting better heat.
5) This past weekend I drove from NJ to Boston and back.
6) Last night I tried the heat again and it was working really well and it was HOT.

So I'm wondering if the dealer mechanic didn't properly bleed the air out of the heater core and in reality my core is fine...

Also, does anyone know when the nipples coming through the firewall were changed from plastic to aluminum? Or were they plastic the entire production run of the B5.5?
 

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I'm willing to bet it's / was just air in the system.

As far as I know the factory heater cores had the plastic heater nipples. It was the aftermarket versions that went to all aluminum construction.
 
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I'm willing to bet it's / was just air in the system.

As far as I know the factory heater cores had the plastic heater nipples. It was the aftermarket versions that went to all aluminum construction.
Didn't even know they made aluminum ones. Family friend picked up a 2.8 A4 recently and it has a bad heater core, gotta help him with that before the harsh winter, might consider getting one of those aluminum ones.
 
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