Coolant Expansion Tank Overflow Nipple?

[bpark1210]

My S6 4.2 has been leaking coolant from the underside of the expansion tank ever since I picked it up. At first I figured it was from the rear coolant pipe O-rings but over the weekend I ran her pretty hard and had a constant dribble coming from the bottom of the tank right onto the CAT which poofs up into a white smoke cloud. Almost shat my pants thinking I overheated the engine and blew a gasket causing white plumes of smoke coming up. When I pop'd the hood I could clearly see the coolant was dripping off the bottom of the tank.

Ordered a new tank and when it arrived it dawned on me that there is a nipple on the bottom of the tank which seems to be for overflow. Am I missing something here in assuming that's what it is or does my S6 have a disconnected hose there? For now I've blocked off the nipple w/ a rubber grommet and hose clamp to keep it secure. All the other openings on the tank have hoses connected but the one nipple is just exposed.

It seems very idiotic to have an overflow right over the CAT which just burns off the coolant and for me at least causes huge plumes of white smoke/steam.




Here's some pics of the new tank for reference:



underside of tank, I'm referring to the small nipple in the middle



close up of suspected overflow nipple



upright view of tank

[glennda5id]

First off, the system should only overflow in the event of over heat or over pressure.

Second, there should be a hose attached and you can put the hose behind the heat shield so it drains to the ground.

[bpark1210]

Thanks for the info. Now I'm curious as to why I'm overflowing, no signs of overheating. Hmmmmm. I'll attach some fuel grade hose to the coolant nipple thanks for that reply.

[glennda5id]

I doubt you are overflowing through the overflow. It overflows through the top of the tank at the cap and then flows to the nipple. Kind of a hidden passage.

The tanks develop cracks overtime. Your current tank is probably cracked and leaking.

[bpark1210]

Yeah that seems to make the most sense. It is the lowest point of the expansion tank therefore would collect and dribble off of there. I bought the tank so will replace it eventually.

Thanks again glennda5id

[02 A6 2.7T]

Thanks for the info. Now I'm curious as to why I'm overflowing, no signs of overheating. Hmmmmm. I'll attach some fuel grade hose to the coolant nipple thanks for that reply.

I noticed that mine didn't have an overflow hose or any indication there was ever one attached to the nipple. The pressure relief valve is built into the blue tank cap, which should be replaced if you haven't already done so. It should hold 15 psi, but finding the right adapter for the rad pressure tester may be difficult ...

[vlangs]

When i was replacing my headlights a few years back I drained the washer fluid and when I poured it back in I mistakenly (stupidly) put it in the expansion tank instead of the washer tank.

Driving it for a few minutes there was clearly too much detergent water in the system (I know i know!) and the thing was bubbling. Carefully releasing a TINY bit of the pressure tripped the overflow valve and let all the excess drain out. Swapping the coolant out solved the issue. But I kept leaking because I never realigned the overflow valve. Once that was put back in place it was all good.

- - - Updated - - -

Oh point being is don't drive like that too long or you'll eventually put a hole in your radiator or burst a radiator line or something

[eclipse1]

What part do I need to fix the radiator overflow nipple that has a crack on my A4 B8?