[lsserekim]

Hi All,
I have a 2008 3.6L Touareg that has started leaking windshield washer fluid out of a molded hole in the fitting on the top of the reservoir (PN 7L0955453F) which I confirmed using a fiber optic camera. My question is, does anyone know what this fitting is supposed to be there for? (I circled it in the attached photo) Is it supposed to act just as plug, or an air path or as some sort of overfill protection? If it's just a plug, it's failed and I'll need to replace it. If it's protection against overfill or freezing, I'll leave it alone.

I can't seem to find a description of this anywhere. Any help would be appreciated.

 

[Gnits]

Looks like an overflow valve to me. If it's that, it's normal that it leaks when the reservoir tank is full.


I for one always wondered why I seemingly couldn't ever pour so much fluid into the tank, that I'd see its level raise in the filler tube. This valve could explain why.

 

[schootsie]

Doubt it is protection against overfill as the cap is not that tight that freezing wouldn't pop it off. Also I have filled mine to overflowing many times as the fluid comes up the neck really quickly when almost full. Only leak I have had (and a few others on the forum) is from the pump unit itself. John

 

[lsserekim]

Doubt it is protection against overfill as the cap is not that tight that freezing wouldn't pop it off. Also I have filled mine to overflowing many times as the fluid comes up the neck really quickly when almost full. Only leak I have had (and a few others on the forum) is from the pump unit itself. John

Hi!
Thanks for the replies! (BTW neat fact: water expands ~10% in volume upon freezing, which makes it unique in world and the reason life exists as we know it on earth - but I digress... ha-ha).
Gnits - I agree with you that it looks like an overflow, and could explain why your observation is the same as mine, that if I intentionally try to overfill the filler tube, it won't stay filled to the very top of the tube for long. I can watch it flow out from this orifice, down the side of the reservoir and then out the bottom of the vehicle. It is pretty slow flow on my T, so I had to fill the tube to the top and wait about 2-3 minutes to see the level drop. But I verified that the fluid does leak from this orifice by watching it with my camera probe; it is NOT leaking from any other point in the system - I triple checked that. So, good to know others may be seeing the same effect. But unfortunately this doesn't answer if this is actually a designed "feature", or a problem we are both experiencing. It may be there to just allow trapped air to escape the reservoir during filling so the fluid doesn't burp back at you.

Shootsie - you are for sure correct about the filler cap. It is loose, so air (and liquid fluid) should escape easily.

However, the design of the filler tube (from the inlet where you pour in fluid to the port where it dumps into the main reservoir) is pretty horizontal, so some fluid should show up in this tube if you fill the system with fluid (but maybe not). And maybe the tube is completely filled along its path in this case (although it's very hard to see this - and I was not able to prove it - I did have the cowl off the wheel well, but I couldn't get a light behind this tube through its full length to see its fill state properly).

Either way though, upon freezing, the fluid (mostly water) expands in all directions, and the pressure is immense (just look at granite boulders on a northern beach and you can see how this pressure fractures them even though the cracks are open to the air).

This tube is only pressure fit to the reservoir using a gasket which helps for alignment, but may also act to relieve some of the pressure as the fluid freezes in the tube (and in the reservoir).

Likewise any fluid that freezes in the reservoir, does so from the outside in, and will expand in all directions and although the port could relieve air pressure build up in the reservoir, it probably can't relieve the freezing fluid pressure significantly. Especially front to back in the reservoir - which is shaped as a V likely not just to fit in the space, but may also to give the forming ice cube an additional upwards lift to help relieve this pressure on the reservoir walls.

As you note most leaks seem to be around the pump unit which is consistent with this - I haven't heard of anyone seeing a crack in the wall of the reservoir from freezing (but I'm new to this forum, so maybe I missed those earlier responses).



So I am left with the idea that this orifice is there to a) maybe allow excess fluid to escape - which may keep the fluid from completely filling the fill tube and/or anti-burping (per Gnits), or b) maybe allow air/fluid to escape the reservoir during freezing (per Shootsie), or c) something completely different.


I suppose if there is some way to contact VW design engineers we may be able to get to the bottom of this.

Anyone have a contact there?

Any ex/present VW washer reservoir design engineers on this forum?


Thanks again!

 

[Gnits]

Doubt it is protection against overfill as the cap is not that tight that freezing wouldn't pop it off.

For one, an overflow valve is not there to protect against freezing, but against overfilling of the container. Freeze protection (or at least mitigation) is provided by freeze plugs. But a valve/plug at the top of the tank (and only there) would do a lousy job at freeze protection anyway, as obviously freeze would start at the bottom ad on the sides first, but definitely not at the top - at least not according to laws of thermodynamics in a non-zero gravity environment. And with a plastic container of the size and shape of the fluid reservoir I doubt it would be necessary in the first place, because the plastic should be able to handle any expansion of the fluid. Even if it doesn't, it wouldn't be a very expensive repair - at least compared to a freeze in for ex. the engine block, anyway.

The other thing is, that with the washer fluid tank, overflowing at the cap could be the worst possible thing that could happen, because the turbo is located right under it, and it would most likely crack when ice cold water would spill onto it while the engine is running. That would also be a good reason to place an overflow valve somewhere else on the thank.

That said I have no clue what the thing is. But since it's not connected anywhere, the most logical conclusion would be that it's some kind of release valve.

 

[lsserekim]

Hi Gnits,
Thanks for the ideas.
I don't have a turbo, so I missed the overflow problem in that area that it might cause.
Regarding the freezing of water. Water (even contaminated water = washer fluid) is just weird stuff - nothing about it is obvious. I really wish it was... Density increases as you go from room temp down to about 4 degrees C, then it decreases by about 10% as it freezes at 0 degC, then increases ever so slightly (<1%) as you go down to -50 deg C. That's important as it sets up convection currents that make the fluid at the bottom of the container potentially the warmest near 0 deg C, so it may freeze last (think ice on a pond). Of course, the relatively faster heat conduction paths through the walls will likely trump the convective air cooling from above (air is a pretty good insulator), so it may freeze bottom to top. It's just weird. I tried modeling this once for a ice-fighting consulting gig and gave up, I could make the stuff freeze top to bottom, left to right, any way I wanted to, depending on the fine details of the simulation... ended up doing it all empirically.
Anyway, good discussion!