# 2001 Passat - Little heat at idle - aux H20 pump



## mikegcc (Sep 26, 2006)

I was wondering if anyone can confirm or deny that the aux water pump is responsible for circulating water through the heater core at idle speeds? 

Heat is ok at cruising speeds (3000 rpms) but falls to below acceptable levels at idle. I have read about an aux water pump and have heard that it is only for circulating water through the block after the car has been turned off. I have also read that it is responsible for circulating water through the heater core at idle speeds. 

Can anyone tell me which is correct? 

My mechanic is replacing my heater core today, the core has been flushed many times. In & Out temps are about 160 in and 140 out or somewhere in that range. The car just doesn't produce acceptable levels of heat output at idle.


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## mikegcc (Sep 26, 2006)

*additional information*

I guess it turns out my model does not have the aux water pump per my mechanic so it looks like I am getting a new heater core. I will post and let everyone know if it fixes the problem.


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## Slimjimmn (Apr 8, 2006)

just an fyi all v6 passats have an aux water pump from 2000+ 

Its on the passenger side of the engine above the alternator under the cylinder head. It turns on after the car has been ran when its operating temperature. 

the 1.8t do not have an aux water pump (even though they really need one)


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## mikegcc (Sep 26, 2006)

Thanks for getting back to me. I do recall seeing fluid "running" back into the reservoir after turning the engine off. I always thought it had something to do with lack of vacuum (or pressure or something) after turning off the engine but it must be that aux water pump.

I have had the heater core flushed in both directions multiple times by at least 4 different mechanics including 2 dealers. I am not sure if any of them have used a vacuum airlift when refilling as you suggested in your email (I appreciate it). Nor have I tried to replace the cap but I will certainly get a new one if the new heater core is not the problem.

Can you confirm the aux pump is necessary for heat at idle? 

Unfortunately, the mechanic is already in the process of replacing the heater core. I know, expensive job ($800-is that reasonable, I thought so?) if its not the problem but this problem has been haunting me :banghead: for a couple of years now and neither 2 dealers or 2 private mechanics have been able to get my heat working properly. I don't want to get rid of the car so I figure I gotta try everything. I have put so much money into people diagnosing and not fixing this problem that a new heater core will eliminate an unknown.


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## Slimjimmn (Apr 8, 2006)

the aux water pump only circulates coolant after the car is turned off


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## mikegcc (Sep 26, 2006)

The mechanic put a new heater core in my car and it fixed the no heat at idle problem I was experiencing.

The core weighed about twice what a new heater core weighed when he took it out. It also had water trapped inside that would not come out. Various tubes were clogged that he couldn't even blow air through.

He said when he initially took it out there was a gelatin like substance that he wasn't sure where it had come from. It solidified after about a day exposed to the air and that it isn't anywhere else in the cooling system that he can tell.

In any case, I am back into 20 degree & lower outside temps and warm & happy with the results :biggrinsanta:. Thanks for your input Slimjimmn and I appreciate you clarifying the purpose of the aux water pump.


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## kobe82 (Dec 27, 2003)

*next time... CLR flush the heater core...*

IT WORKS>>

chris


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## Slimjimmn (Apr 8, 2006)

This is the sole reason why you should flush your cooling system every 40k miles. I have 128,000 on my passat with much heat to spare original HC


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## ernstn49 (Jul 23, 2011)

*CLR flush*

Does anyone know the proper procedure for CLR flushing a heater core on a Volkswagen Passat? In other words, do we simply add CLR to the radiator and let it circulate for some time? What I also wish to know would be the quantitynof CLR to use and how long should it be circulated?


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## O_o (Nov 12, 2009)

You'd never catch me putting CLR in my coolant. For starters, it will vulcanize your rad hose. And I'm not sure it reacts well with aluminum.


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## Slimjimmn (Apr 8, 2006)

step one - remove both hoses from the heater core
step two - put garden hose up to one pipe and flush the coolant out
step three- blow out the water with compressed air from heater core
step four - top off heater core with clr and let sit overnight
step five - run water through hoses to flush out clr
step six - put hoses on and top off coolant


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