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Failed Thermostat Housing/Coolant Loss Info Gathering

jimlloyd40

Autocross Newbie
Location
Phoenix
Ride
2018 SE DSG
That’s interesting about the cap. My thermostat was replaced this past year and I still smell coolant - although the level hasn’t dropped that I can tell. I guess it could be leaking again, but the smell is mainly near the firewall on the passenger side right around the expansion tank. I don’t see any residue on/around the tank. Is the thermostat/water pump below this area? Maybe I should swap the cap just to see if it solves the issue...
If the level isn't dropping in the overflow tank you don't have a leak.
 

joeblonewjersey

Ready to race!
Location
Metuchen, NJ
Hey idiots who don't work on their own cars....

There is a pressure relief valve on the overflow cap itself. If the valve is failing, vapors escape. That's the coolant you smell under the hood. Eventually the vapor loss adds up to coolant loss.

Read the service manual, it states, when doing coolant pressure test, test the system and ALSO THE CAP. Dealership techs don't read manuals, they don't get paid enough flat-rate time by VW to do so, so they don't know to test the cap.

Look under your coolant bottle, and follow the frame rail. I bet you will see a dirty path that leads to the nose of the vehicle. That's where your coolant is going.
PLEASE, post a picture of the "CAP" and/or its location and/or its part number. Sounds like a stupid request, but nonetheless, it's valuable.
 

stuntnuts

Ready to race!
Location
Maine
PLEASE, post a picture of the "CAP" and/or its location and/or its part number. Sounds like a stupid request, but nonetheless, it's valuable.
Ok after I "look" at it, what am I "looking" for?
Are you serious here? Do you not know what or where your coolant overflow bottle is? Seriously?

It's the little tank in the passengers side of the engine bay that holds the pink Kool-Aid.



Please turn in your Man Card and trade in your VW for a Hyundai. Please and thank you.
 
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ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
Are you serious here? Do you not know what or where your coolant overflow bottle is? Seriously?

It's the little tank in the passengers side of the engine bay that holds the pink Kool-Aid.

Please turn in your Man Card and trade in your VW for a Hyundai. Please and thank you.
Can you please calm down and be respectful, or simply leave. Those are the adult choices you can make at this point.

This thread is not for insulting comments and acting like a 12 year old.

This thread is for info gathering on this topic based on observed and verified evidence. You have provided observations, but no verification of said observations and have failed several times to address it when asked.

Thank you.
 

joeblonewjersey

Ready to race!
Location
Metuchen, NJ
Are you serious here? Do you not know what or where your coolant overflow bottle is? Seriously?

It's the little tank in the passengers side of the engine bay that holds the pink Kool-Aid.



Please turn in your Man Card and trade in your VW for a Hyundai. Please and thank you.
Thanks for posting the picture. I was not aware that the cap has a pressure release as well as seal. Given most radiator caps from era past were different, it's different to see it on a plastic bottle of sorts. Thanks for posting. I've got 24k miles on my '16 GTI-S and smell antifreeze. However I have no loss. Mannin' up!
 

jimlloyd40

Autocross Newbie
Location
Phoenix
Ride
2018 SE DSG
Not true. A MINOR vapor leak out of the cap is enough to cause the smell, but not necessarily enough to drop the coolant level any noticeable amount.
Well if it isn't dropping the level any "noticeable" amount as you said then it's not leaking. Plus you can get air in the system if there's a vapor leak. If the vapor can leak out air can get in.
 

jimlloyd40

Autocross Newbie
Location
Phoenix
Ride
2018 SE DSG
Are you serious here? Do you not know what or where your coolant overflow bottle is? Seriously?

It's the little tank in the passengers side of the engine bay that holds the pink Kool-Aid.



Please turn in your Man Card and trade in your VW for a Hyundai. Please and thank you.
Hey I've had two Hyundais and I knew where the coolant overflow tank was. 😂
 

joeblonewjersey

Ready to race!
Location
Metuchen, NJ
Eh, I'm not stupid, so with that RTFM: https://cartreatments.com/radiator-coolant-overflow-tank/
Pay attention to the end.....stuntnuts
"The coolant tank overflow is non-pressurized on almost all modern vehicles (if the cap is plastic, it’s non-pressurized). That said, as coolant heats up it expands. So if you don’t have a tight seal, coolant can leak out and ultimately cause you to be low on coolant which would cause overheating. Check your coolant level and if you notice the level decreasing, get that cap replaced asap".
So, if it is plastic (it is) and if it needs a "pressure test" (so stated by the 'expert', but actually it is not?), how is it then it can be faulted?
Also, please show me where the "pressure relief valve on the overflow cap itself" exists.
Education is key, that is the purpose of these types of forums.
I know a lot, so if my questions seen stupid to some, excuse my ignorance, we all learn by asking questions.
 

stuntnuts

Ready to race!
Location
Maine
Eh, I'm not stupid, so with that RTFM: https://cartreatments.com/radiator-coolant-overflow-tank/
Pay attention to the end.....stuntnuts
"The coolant tank overflow is non-pressurized on almost all modern vehicles (if the cap is plastic, it’s non-pressurized). That said, as coolant heats up it expands. So if you don’t have a tight seal, coolant can leak out and ultimately cause you to be low on coolant which would cause overheating. Check your coolant level and if you notice the level decreasing, get that cap replaced asap".
So, if it is plastic (it is) and if it needs a "pressure test" (so stated by the 'expert', but actually it is not?), how is it then it can be faulted?
Also, please show me where the "pressure relief valve on the overflow cap itself" exists.
Education is key, that is the purpose of these types of forums.
I know a lot, so if my questions seen stupid to some, excuse my ignorance, we all learn by asking questions.
The overflow tank IS pressurized, you fool. If you don't believe me, by all means, go for a nice long drive and park your car. Pop your hood and open your coolant overflow tank cap. You'll feel the pressure.....all 200+ degrees F burning all over your face. I'm serious, please, try it.

Anyways, back to the evidence of a coolant tank cap leak......Look for a trail of dirt that starts below the coolant bottle and travels down to the front of the vehicle, along the frame rail, like in this pic:

01.jpg


I've had two Mk7's and they both demonstrated this. THAT is your vapor leak. Some are worse than others. As you drive, the dampness attracts dirt to the path and when it dries, the dirt remains.

The overflow tank is SUPPOSED to release pressure IF the pressure gets too high, to protect the system. The problem is these caps are releasing pressure at too low of a pressure, intermittently.

Here's the VW Factory service manual describing the PROPER testing procedure, for you idiots who don't believe me:


1.jpg


2.jpg
 
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ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
Anyways, back to the evidence of a coolant tank cap leak......Look for a trail of dirt that starts below the coolant bottle and travels down to the front of the vehicle, along the frame rail, like in this pic:

I've had two Mk7's and they both demonstrated this. THAT is your vapor leak. Some are worse than others. As you drive, the dampness attracts dirt to the path and when it dries, the dirt remains.

The overflow tank is SUPPOSED to release pressure IF the pressure gets too high, to protect the system. The problem is these caps are releasing pressure at too low of a pressure, intermittently.

Here's the VW Factory service manual describing the PROPER testing procedure, for you idiots who don't believe me:
Now see? That is HELPFUL, evidence-based, information we can all look at and say, "Oh, hey, cool, we can look at this from another angle now."

Thanks for posting the information.

Two questions:

Was the solution to just replace the reservoir cap? Do you mind editing the post to reflect that solution? Thanks.
 
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zero10

Ready to race!
I thought the dirt buildup there was the result of some sealant or something during the manufacturing process... I've got a buttload of dirt and grit stuck on there but it doesn't rub or wash off, it's been there since the car was new. I also have a slowly dropping coolant level so I'll pay closer attention to that spot and see.
 

stuntnuts

Ready to race!
Location
Maine
Two questions:

Was the solution to just replace the reservoir cap? Do you mind editing the post to reflect that solution? Thanks.
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.
 

stuntnuts

Ready to race!
Location
Maine
I thought the dirt buildup there was the result of some sealant or something during the manufacturing process... I've got a buttload of dirt and grit stuck on there but it doesn't rub or wash off, it's been there since the car was new. I also have a slowly dropping coolant level so I'll pay closer attention to that spot and see.
That line of "dirt buildup" was not there when I bought my vehicle, nor did it have the sweet aroma of coolant under the hood. It now has 6,500 miles on it.
 

theDoktor

Ready to race!
Location
Buffalo, NY area
Good info @stuntnuts. Unfortunately my Mk. 7 gets driven in the winter plus it has Krown rustproofing. I'm going to have to clean off the excess rustproofing on the frame rails when spring finally arrives before I can isolate any possible overflow tank leakage. Right now, it's just a mess!
 

joesid

Ready to race!
The overflow tank IS pressurized, you fool. If you don't believe me, by all means, go for a nice long drive and park your car. Pop your hood and open your coolant overflow tank cap. You'll feel the pressure.....all 200+ degrees F burning all over your face. I'm serious, please, try it.

Anyways, back to the evidence of a coolant tank cap leak......Look for a trail of dirt that starts below the coolant bottle and travels down to the front of the vehicle, along the frame rail, like in this pic:

View attachment 165070

I've had two Mk7's and they both demonstrated this. THAT is your vapor leak. Some are worse than others. As you drive, the dampness attracts dirt to the path and when it dries, the dirt remains.

The overflow tank is SUPPOSED to release pressure IF the pressure gets too high, to protect the system. The problem is these caps are releasing pressure at too low of a pressure, intermittently.
Here’s mine, it goes in for service in a week. I’ve lost about 16oz since my last service (7,500k) and have no clue where it’s gone.
68A5BBDB-08E6-4C43-B12C-B6DACB642A6C.jpeg
 
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