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Failed Thermostat Housing/Coolant Loss Info Gathering

dequardo

Drag Race Newbie
Location
Waukesha, WI
I haven't replaced the cap yet, so for me to say it was resolved would be dishonest. I don't do dealerships, and I haven't gotten to replacing the cap myself yet, but I know it's the issue.

My last Mk7, in the middle of the summer, you would actually see drips of coolant in that path. My current Mk7.5 just started doing it in the fall and I don't drive it in the winter, so I haven't addressed it. In the current car, I detect a slight odor on occasion, but not nearly as bad as my Mk7. I haven't seen any actual drips on this one yet. Just the dirt magnet vapor path.
Odd that you are so strident about this issue but have not yet addressed it yourself for the pittance of a new cap.
 

stuntnuts

Ready to race!
Location
Maine
Odd that you are so strident about this issue but have not yet addressed it yourself for the pittance of a new cap.
Odd, you say? My first car to exhibit this behavior was bought back by VW. My current car exhibiting this behavior just started doing it before I parked it for the winter. I avoid the dealership at all costs. I'm not going in there because my $20 coolant bottle cap is leaking to get it fixed under warranty. When I begin driving this car again in a month or two, I'll address it.

I'm stringent about it for OTHERS who have been strung along by VW dealership repair facilities, with their inability to recognize and solve simple car problems.
 
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joesid

Ready to race!
This might be a dumb question, but I'm under the assumption that when the cap fails, the leak doesn't come from cap area. Is this correct? Is coolant pushed through one of the hoses attached to it? and where to?

Weird fact: I used to have an old W124 Mercedes that had a hidden coolant recovery tank hidden behind the fender.
(Not my car)
2AA54444-F588-446B-BA4B-15D26837CEC0.jpeg
 
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stuntnuts

Ready to race!
Location
Maine
This might be a dumb question, but I'm under the assumption that when the cap fails, the leak doesn't come from cap area. Is this correct? Is coolant pushed through one of the hoses attached to it? and where to?
The seal on the cap releases pressure and diverts the relieved coolant (or just vapors) out of the bottle itself (behind the bottle), where you can't see. For lack of a better term, there's a "gutter" in there. In severe cases, it drips down onto the frame rail and that is what creates the "dirty path" in my original picture.

In this pic, the "gutter" is flipped up. That's where the escaping coolant/vapor goes and drips down onto the frame rail.

Borrowed pic:

 
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ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
Anyone know the part # for the coolant reservoir cap?
5Q0 121 321

List price is $39:ROFLMAO:

73C0 121 321end cap
81H0 121 687 Ao-ring
Would replacing the o-ring suffice, I wonder? Is it the cap itself that is failing or is the o-ring just not good enough to withstand the temps/chemicals it is seeing?


I wonder if there is an o-ring made of Viton (higher temp rating and chemical resistance) that is a correct replacement.
 
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stuntnuts

Ready to race!
Location
Maine
So, then, IF the gutter has evidence of some sort of escaping vapor or liquid, what needs to be done? The "O" ring, the cap, or?
I don't know for sure, but I think the seal isn't the issue. There's a pressure rated valve in the cap. That is what coolant escapes thru. This valve bypasses the seal. Again....speculation.
 

stuntnuts

Ready to race!
Location
Maine
So probably best to replace both the cap and the o-ring if you don't want to deal with a dealer visit.
The o-ring comes with the cap already installed. It would probably be wise to verify that the cap is failing with the pressure test specified in the Factory Repair Manual excerpt I posted, so you aren't just throwing parts at it blindly.
 

AtlantaDad

Go Kart Champion
Location
Cumming, GA
So...been away for a while and not sure if this has been answered...

What's the cost to fix the water pump/thermostat housing issue if you're out of warranty? Curious, since I'm sure mine will need it at some point (have to top off fluid fairly regularly).
 

ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
Yeah I'll check with some of the local FB group guys who do side work. I don't think I could do it myself.
Yeah, I watched the DIY and it's pretty involved. Not something I'd personally want to tackle for my first time alone, never mind I don't have the time with my 3 year old in the mix. Thankfully I still have 2/20k of warranty left.
 
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