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Discussion Starter #1
Like many others, I'm singing the no-heat blues... However, I wonder if there's something else at play here than the usual suspects. Here's what I know:
-My coolant reservoir isn't dirty
-My coolant isn't dirty, is the proper G12, and was fully flushed about a year ago
-About a year ago my local mechanic replaced the water pump, but not the thermostat
-I just did the CLR flush of the heater core, and it seemed to flow through OK, it came out clean without any debris or deposits, but still didn't improve the heat
-When the car is fully warmed up, the hoses to the heater core aren't very hot
-Never seen the water temp gauge at more than 1/2 way (normal operating temp) so I don't think the engine is overheating
-When the car is cold and warming up, there's *warm* (not hot) air coming out of the vents when the heater is turned on
-However, once the car fully warms up, the air coming out the vents is much cooler (less warm)

So, I'm really curious about exactly how the coolant flows... There are a ton of hoses, and I can't seem to figure it out (without taking the whole thing apart).

Is there a possibility that due to a faulty thermostat or some control valve the coolant is just circulating in a loop that's excluding the heater core?

Could this be a failing impeller on the water pump?

Or, is there some internal restriction/failure in the heater core?

If someone could point me towards a diagram or a description, I'd much appreciate it. (My wife isn't happy driving a cold car in upstate NY!)
 

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Is there a possibility that due to a faulty thermostat or some control valve the coolant is just circulating in a loop that's excluding the heater core?
No, except for a blockage in the heater core.


Could this be a failing impeller on the water pump?
Possibly, but you would likely have overheating problems.


Or, is there some internal restriction/failure in the heater core?
Possibly.


-About a year ago my local mechanic replaced the water pump, but not the thermostat
-When the car is fully warmed up, the hoses to the heater core aren't very hot
-Never seen the water temp gauge at more than 1/2 way (normal operating temp) so I don't think the engine is overheating
It could be a faulty thermostat (Stuck open).


-When the car is cold and warming up, there's *warm* (not hot) air coming out of the vents when the heater is turned on
-However, once the car fully warms up, the air coming out the vents is much cooler (less warm)
There could be a fault in the temperature control flap.


Do you have manual or Climatronic controls ?
 

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Discussion Starter #4
Thanks guys, it probably should have mentioned that it's the 1.8T... and the climate control knobs are the turn-style. And all the flaps seem to be working - there's lots of air volume, and you can make it go to the dash vents, defroster or floor - it's just luke-warm at best.

Ylwagon, looking at that diagram, it seems like the thermostat will open or close that "Bypass" pipe that runs from the back of the engine to the water pump. When that Bypass is open, there is really suction on both sides of the heater core - the outlet (passenger side) that goes to the water pump, and the tee off the Bypass.

If my thermostat isn't fully shutting off the Bypass, then that will continue to be a "path of least resistance" and the water pump won't be able to force much coolant through the heater core.... Sound logical?
 

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i have the exact same problem with my 03 1.8t passat... i had gone to the dealership and said that my thermostat was stuck open.
i went to another place so they could change it, did a pretty good job. this was back in summer, now in winter my heat is like you said "luke-warm" at best.
can my thermostat be stuck open again??
 

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i have the exact same problem with my 03 1.8t passat... i had gone to the dealership and said that my thermostat was stuck open.
i went to another place so they could change it, did a pretty good job. this was back in summer, now in winter my heat is like you said "luke-warm" at best.
can my thermostat be stuck open again??
You probably have a clogged heater core, or possibly a faulty temp control flap. Search heater core flush.

Here's some info on heater core flushing.

Heater Core Flush
Always reverse flush, connect the feed hose to the outlet (the one with the bleeder), and the drain hose to the inlet.
You will need to obtain a high flow, without reaching high pressure in the core.
NOTE: A CLEAR CORE will easily take all the flow you can get from a 1/2" garden hose, without building up pressure in the core.

You should NEVER forward flush a core with any blockage, this is likely to pack the core so tight that you may never remove the blockage with any method.


I suggest you try this method, see the homemade tool.


OTC 6043 Blast-Vac Multipurpose Cleaning Gun : Amazon.com : Automotive

http://www.passatworld.com/forums/68-b5-garage/355695-homemade-heater-core-flushing-tool.html

If you have a clogged heater core your options are:
1: Do nothing. (Shiver)
2: Replace the core. (Big job)
3: Flush the core clean. (Some risk of damage to core) Worst case you still have options 1 & 2.


Heater core swap.
Heater Core Swap - PassatB5


If you want to use a chemical solvent (such as CLR or Citric Acid), first reverse flush with water or water and air, then blow the water out of the core with compressed air,
then fill the core with chosen chemical and allow to soak. Repeat reverse flushing. Finish with a forward flush.

See this thread.
http://www.passatworld.com/forums/42-volkswagen-passat-b5-discussion/364634-no-heat-my-passat.html
 

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All the flaps seem to be working - there's lots of air volume, and you can make it go to the dash vents, defroster or floor - it's just luke-warm at best.
This doesn't indicate that the temp control flap is working, I suggest you check it.


Ylwagon, looking at that diagram, it seems like the thermostat will open or close that "Bypass" pipe that runs from the back of the engine to the water pump. When that Bypass is open, there is really suction on both sides of the heater core - the outlet (passenger side) that goes to the water pump, and the tee off the Bypass.

If my thermostat isn't fully shutting off the Bypass, then that will continue to be a "path of least resistance" and the water pump won't be able to force much coolant through the heater core.... Sound logical?
You have interpreted this incorrectly, the thermostat blocks the flow between the bottom radiator hose and the bypass,
and has very little, if any effect on the flow through the heater core.

The only things at all likely to effect the flow through the heater core are:
1: Clogged core.
2: Kinked heater hose.
3: Failing water pump.
 

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Here is a diagram for the 1.8t (AEB, ATW, but others are similar). I put a red circle where the thermostat is.

13 is commonly referred to as the coolant flange, where the coolant temp sensor sits as well.

Coolant flows through the heater core all the time, regardless of tstat position, or heater controls.

The dial on the console adjusts air flow via a flap that controls how much of the air goes through the heater core fins or around the heater core.
 

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Discussion Starter #9
Thanks all - I did some serious flushing with a garden hose hooked up to the outlet of the heater core (I had to make up some interesting fittings... and I used a ball valve so I could turn it on and off).

At first, it didn't seem like much was flowing through, so I started opening and closing my ball valve as rapidly as possible - trying to get a pulse effect - and all of a sudden, all of this white flakey stuff started coming out. I kept at it until my fingers were frozen, and I'm happy to say I have probably 90% of my heat performance back.

I'm going to buy that flush gun on Amazon and give it another round when it shows up.
 

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i just cleaned my MAF and changed my air filter, and today i figured i tried the heater, and to my surprise
it worked!!!! and it was blowing strong and hot. so i guess cleaning the MAF helped??
 

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I need to change the lower coolant line because of numerous holes I found in it, how do you release it from the front of the engine near the thermostat housing?
 
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