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in dire need of an organic chemistry lesson
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Discussion Starter #1
Tried unsuccessfully to change the coolant tank today. I have put the old tank back with full of coolant. But when I started the car I get this alarm light on. What would be the cause of this?
Could it be that there is air in the system preventing coolant to freely flow? If so how do I get the air out of system?

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in dire need of an organic chemistry lesson
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2,319 Posts
Discussion Starter #2
Tried the tank cap off and heater nob to max while running at 2000 rpm but still no air comes out.

Are there any bleeding holes or something like that anywhere? I seem not even to find the two hoses going to the heater core. Where are they located anyway?
 

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How exactly did you fail to replace the tank? It's one of the easiest jobs on the car. The heater core hoses are under the water plenum cover at the back of the engine compartment. Remove that (as though you were getting at the battery) and it should be obvious. I've never seen that exact warning... but are you sure you didn't break or disconnect the coolant level sensor at the bottom of the tank?
 

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in dire need of an organic chemistry lesson
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Discussion Starter #4
How exactly did you fail to replace the tank?
I bought one of the crappy fake Chinese tank off the eBay. This morning tried to replace it but at the end the coolant level plug did not fit in it no matter how I tried. So I put the old tank back but when I started the car I got this warning which scared a whole shit outta me because I thought now the headgasket is gonna blow up.

It's one of the easiest jobs on the car.
Actually nothing (absolutely nothing) is easy on German cars especially VWs. But I do agree that this one ain't complicated until you get the red alarms.

The heater core hoses are under the water plenum cover at the back of the engine compartment. Remove that (as though you were getting at the battery) and it should be obvious.
OK, went back and found them. Then with the bleeding hole I was able to get the air out of the system. So for now I'm saved agai till next dooms day.

I've never seen that exact warning... but are you sure you didn't break or disconnect the coolant level sensor at the bottom of the tank?
No it's not broken although it may have not sit there tightly. However, this alarm was not because of that because when I bled the system it was gone.
 

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No it's not broken although it may have not sit there tightly. However, this alarm was not because of that because when I bled the system it was gone.
Ah. I've changed a few coolant tanks in my day, and never gotten enough air in the system to get that warning. Last time around (a few weeks ago) I only lost about a cup of coolant.
 

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That warning should only be activated when the coolant level in the tank falls below a certain level. There is no 'air detection' sensor in the system.

Are you sure you connected the coolant level sensor to the tank properly? Or.. alternatively... did you damage the connector when trying to attach it to the cheapo ebay tank?
 

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It's much more likely that the sensor built into the chinese tank is faulty, that's why it triggered the red alarm in your dash. The "sensor" itself seems to be just a couple of metal pins that get immersed in the coolant. If these pins do not get submerged the car will know there's not enough fluid causing the red alarm to beep.

I also replaced my tank by this chinese one, so far I did get one of those alarms but I guess it was related with the wiring not being properly attached to the bottom of the tank. After reconnecting it the alarm was gone but I still got the old one in the trunk "just in case".
 

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in dire need of an organic chemistry lesson
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Discussion Starter #10
never gotten enough air in the system to get that warning
During exchange of the tanks quite a lot of coolant was lost. When I put the old tank back and filled it, I guess there was air in the hoses since I couldn't see any coolant in them.
 

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in dire need of an organic chemistry lesson
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Discussion Starter #11
Are you sure you connected the coolant level sensor to the tank properly? Or.. alternatively... did you damage the connector when trying to attach it to the cheapo ebay tank?
I had made sure that the connector was in place and clicked when I pushed it. I don't believe the connector is damaged since it is working properly now. Whether during the installation the connector come off I can't tell for sure. It's a possibility. But there were plenty of coolant in the tank.
 

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in dire need of an organic chemistry lesson
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Discussion Starter #12
It's much more likely that the sensor built into the chinese tank is faulty, that's why it triggered the red alarm in your dash.
I did not get the alarm with the Chinese tank. It came when I reinstalled the old tank. It could have been caused by the connector. Nevertheless, I bled the system and lot of bubbles came out of the tank.
 
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