Coolant tank overflow hose, where does it go?

[daughtersA4]

Does anyone know where the coolant overflow line at the top rear of the coolant reservoir goes? It appears to go to the rear of the engine and connect to something. Curious where it overflows to. Thanks.

[Theiceman]

I had no idea there was a hose I thought it just ran out the bottom of the tank from the cap

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[Spawne32]

https://www.ecstuning.com/b-genuine-...e/8k0121081ah/

goes to the rear coolant flange i believe

[old guy]

Does anyone know where the coolant overflow line at the top rear of the coolant reservoir goes? It appears to go to the rear of the engine and connect to something. Curious where it overflows to. Thanks.

That isn't an overflow hose. It is part of the coolant circulation. The coolant overflow exits underneath the coolant reservoir as noted by Iceman. If you remove the reservoir cap you can see the overflow port.

[Spawne32]

That isn't an overflow hose. It is part of the coolant circulation. The coolant overflow exits underneath the coolant reservoir as noted by Iceman. If you remove the reservoir cap you can see the overflow port.

lol yeh there is no overflow line on a sealed cooling system, but i knew what hose he was talking about, in fact im surprised they dont break more often given that they use that shitty hard plastic that gets brittle when its cold.

[Smac770]

I thought this would be fun; I should have known better. Here's the coolant hoses diagram from the repair manual. As already pointed out, that hose goes to the coolant flange on the back of the engine.

B8 A4 coolant hose connection diagram.png

What's odd, once I had to start looking into this more because of the HVAC stuff, is that the additional coolant pump V50 is not where it should be. It's only present on stop/start equipped cars it seems, and it would be on the return line from the heat exchanger, just under the coolant switch-off valve. Not sure why it was drawn on the supply line.

I thought it might be more interesting to add the part numbers, or at least the ETKA part references.

B8.0 A4 2.0T coolant hose connection diagram ETKA part numbers.png

So that should be correct for a US B8.0 A4 2.0T. Stuff changes up for the B8.5, and gets more convoluted with the different engines for automatic vs manual.
The numbers refer to the part number on https://nemigaparts.com/cat_spares/e...q/636u/121310/
For ones that are references to a different page, like all the 40s, the part number on the referenced page is after the slash.
So the coolant pump is part 42 on the cooling system page, and when you follow the link to the coolant pump page, it's part 1. So I called it 42/1.
Some are the same page. 42 and 43 go to the coolant pump page. 44 and 46 go to the heater hoses page.

Needless to say, this turned out to be a lot less entertaining than originally anticipated.

[Theiceman]

[daughtersA4]

Thanks for all the replies. So if there is no overflow, and the system is overfilled/over heats, is there no escape but to possibly blow coolant lines or the radiator?

[Spawne32]

Thanks for all the replies. So if there is no overflow, and the system is overfilled/over heats, is there no escape but to possibly blow coolant lines or the radiator?

if you take your cap off, and look at the outer part of where the cap sits, you will see its wide open, if the cap releases pressure it releases it to atmosphere

[daughtersA4]

if you take your cap off, and look at the outer part of where the cap sits, you will see its wide open, if the cap releases pressure it releases it to atmosphere

Got it. Thanks!