Cracking Multiple Coolant Reservoirs

A6 All/ S6 All
#1

Bought the car in November and in early December I found a puddle of coolant under my car. Found a crack in the reservoir. I learned through research that this is a fairly common occurrence in these cars.

Bought a new reservoir from JHM. Installed it and had no issues. Today, 4 months later, I found a new crack in the reservoir. It’s at the top of the reservoir so it’s actually not leaking coolant this time, however, it can’t build pressure, lowering the boiling point of the coolant.

I’m going to buy a new reservoir but my question is what would cause reoccurring cracking of the reservoir. I know it’s a common occurrence but 4 months?

Thanks ahead of time.

#2

Is the crack at the cap, near a bolt location, or in a generic area on the top side of the reservoir?

A couple of things could contribute to the plastic cracking - bad/wrong plastic used in manufacture, wrong coolant, incorrect coolant mixture, excessive tightening of cap, excessive bolt/residual stresses. Probably a few other possibilities I’m missing.

Not leveling accusations, just listing possibilities.

#3

The first crack was in the side if the reservoir in flat plastic, nowhere near any bolt location or the cap. The crack in the new one is much closer to one of the top bolt locations on the side closest to the windshield.
I knew being plastic not to tighten it to tight. I did a very gentle snug but I suppose that could still be a culprit to the new one cracking.

The first crack in the old reservoir literally looked like pressure caused it to split and push outward causing a huge crack in the side of the reservoir.

#4

Just wanted to give a quick update.

Finally got the reservoir off this weekend, and wanted to show everyone where my sneaky little leak was.

http://audirevolution.net/addons/albums/images/604104469.jpg

Anyways, I barely snugged the screws this time just to make sure, as well as bought ANOTHER new reservoir cap just to be sure, so we will see how long this reservoir lasts. ::slight_smile:

#5

damn that is an odd location. my guess would be probably not from over-tightening the screws - if it were, the cracks would likely be near the bolt holes or at the junction that the tabs are connected to (generally, mid-radius).

is that an OEM tank? if not, you might want to try a different brand or go OEM. seems like a pressure-related issue to me based on the location, in which case i’m left puzzled! ??? ???

#6

It’s OEM. It is also the new part number listed below.

Part Number: 4F0-121-403-AA
Part: Expansion Tank
Replaces: 4F0-121-403-E, 4F0-121-403-P

Definitely seems like over-pressure to me. No idea why though. The cap should vent at a certain PSI correct?

I’m trying not to bring up the thought of head gaskets :-X
I come from the world of diesel pickup trucks and most of the time, excess pressure in the coolant was a sign of a failed head gasket. I haven’t heard any horror stories about HGs on these cars though soooo…

#7

No 6.0 ford diesel on the Audis LOL.

Heat stress is the main component I haven’t seen any of them crack in that spot. Its odd crack and that wouldn’t be from pressure IMHO you don’t see any sign of distortion that would cause or lead to a crack. Its almost like its an impact crack some how.

Coolant containers are not a super big ticket item but maybe you can plastic weld it.

#8

Come to think of it, if you want I can take a look at it and see where the crack started and can post some pics. I have a microscope at work and do this sort of thing with reasonable frequency heh. I’ll even pay for shipping! :slight_smile:

#9

Dang, if you’d have mentioned that sooner I’d take you up on that out of curiosity, butttttt… I chucked it already. New one is working so I tossed the old one. Sorry! Thanks for the offer tho.

Thank goodness for that. 2nd vehicle I ever owned was an 03 Excursion with the 6.0
We won’t talk about how that went. People think these C6s are maintenance hogs… ::slight_smile:

Anyway, yeah I went the proper route and just bought a new one and installed it. I think I’d rather do that than try to do the plastic weld but I like the idea, didn’t think of it at the time.

I made sure to just barely snug the screws just in case and we will see how it goes this time around. I just wanted to show everyone an uncommon place where this thing could apparently crack and cause slow coolant loss without you even knowing.