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Failed Thermostat Housing/Coolant Loss Info Gathering

DenaliTim

New member
Location
Bay Area
19 SE with 4,700 miles that I’ve had to top off a couple times as it seems to have a small leak. I can smell coolant and haven’t taken it in yet.
 

avenali312

Drag Race Newbie
Location
Smyrna, GA
Ride
2015 VW GTI
Were both pictures taken with the engine at the same temperature?
Correct. Whenever I check the level, I drive to work, park the car, and then check the level around lunch time. So, the engine should be level and cold.

Yeah, this is important, there is a certain amount of expansion/contraction of the fluid. When monitoring my level, I was always looking at cold car, generally first thing in the morning.
Yeah, I have a pretty similar routine for checking mine. See above. Same with checking the oil when I get gas.

Just a heads up and I know technically it's not supposed to happen but I've seen the fluid level change just form air temperature alone. I keep an eye on mine and it will raise when I come back from Michigan (to VA)
Thanks for this. I didn't think the system was supposed to change that much based on ambient air temperature, but I will keep an eye on that the next time I check it. Yesterday was around 45 degrees when I checked it. Historical archives for September last year say it was around 90 degrees. I'm hoping this explains it as I really don't want to deal with another one so soon. I'll keep an eye on it and note the air temp as well from now on.
 

jimlloyd40

Autocross Newbie
Location
Phoenix
Ride
2018 SE DSG
Correct. Whenever I check the level, I drive to work, park the car, and then check the level around lunch time. So, the engine should be level and cold.



Yeah, I have a pretty similar routine for checking mine. See above. Same with checking the oil when I get gas.



Thanks for this. I didn't think the system was supposed to change that much based on ambient air temperature, but I will keep an eye on that the next time I check it. Yesterday was around 45 degrees when I checked it. Historical archives for September last year say it was around 90 degrees. I'm hoping this explains it as I really don't want to deal with another one so soon. I'll keep an eye on it and note the air temp as well from now on.
I highly doubt that ambient temperature will affect the level when the engine is cold. I live in Phoenix where 115 degrees is common and I don't see the level change on a cold engine.
 

BadHombre760

Go Kart Newbie
Location
Viva Las Vegas
I topped off my car for the first time last month (2017, ~21k miles) after noticing it was just right below the MIN mark. Since the car is tuned I'm not sure whether or not sure I should bother bringing it to a dealer
 
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ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
I topped off my car for the first time last month after noticing it was just right below the MIN mark. Since the car is tuned I'm not sure whether or not sure I should bother bringing it to a dealer
See if you can visually verify evidence of the leak to show them. You shouldnt have issues getting coverage for this issue. Other tuned members have had service done.
 

Boltsfan17

New member
Location
Tampa, FL
2017 GTI SE. Low coolant light went on at around 30k. Took it in and had it topped off. Service Advisor said that in Florida it’s not uncommon to lose coolant due to the significant heat. Didn’t really buy that but all seemed ok until about 39k and light came on again. Checked the level and it was very low. Topped it off myself.

After some research to include this thread, there is clearly an issue here. I’ve never smelled coolant and can’t see leak residue but something is happening. I’m due for service in 1k and will definitely bring this to their attention. I’ll report what happens.
 

aaronc7

Go Kart Newbie
Location
Clovis, NM
Try to snap a picture if you can.... like the one I posted earlier. Hard to deny that and should make it easier for them to take a look/start the process. Dealer in florida told me when I bought a new car once that I had to get my oil changed more often with them "because of the heat", what a load of shit, lol.
 

dosjockey

Go Kart Newbie
Location
South
2017 GTI SE. Low coolant light went on at around 30k. Took it in and had it topped off. Service Advisor said that in Florida it’s not uncommon to lose coolant due to the significant heat. Didn’t really buy that but all seemed ok until about 39k and light came on again. Checked the level and it was very low. Topped it off myself.

After some research to include this thread, there is clearly an issue here. I’ve never smelled coolant and can’t see leak residue but something is happening. I’m due for service in 1k and will definitely bring this to their attention. I’ll report what happens.
Obviously I'm new here, and unfamiliar with the Mk7, but I do want to point out that your service advisor may have (hopefully unwittingly) mislead you.

Logically, he's not actually wrong... But I could type a lot of things that are not wrong, and yet would be contextually incorrect.

While there is indeed a causal relationship between extreme heat and coolant loss; that relationship is bound to engine temperature itself. If your engine becomes too hot, you may blow a head gasket, which will certainly cause a coolant leak of at least one variety. Your engine should not reach that point within the region of its delivery. If you dropped a North American spec vehicle off in Dubai... Sure. Maybe. It depends on the manufacturer. I'm not sure how well Volkswagen does, in that regard.

In order for ambient temperature to cause a coolant loss, it must first cause an overheating condition. That's the second iteration of the system. The third is coolant loss.

Unless some new technology has been invented that relies upon ambient temperature to seal the engine itself, there are only a few ways to lose coolant:

1: A leaking seal or gasket.

That may mean whatever seals this leaky part to the block, a heater core, or even a head gasket.

2: Casting porosity.

This is becoming less and less likely over time, but it's possible even on a new car if there is an error in the casting process.

3: Wicking.

This normally a result; not an initial event.

4: Corrosion.

Aluminum is indeed prone to corrosion, and thinner flanges can sometimes begin to leak due to mating interference or simply leaving a passage through which fluid may leak.

Generally, one shouldn't observe coolant level fluctuations associated with ambient temperature, but if that does happen, consider the causal links. As the engine expands and contracts, the level will certainly fluctuate, but that's what those little lines on the reservoir are for; they are meant to account for such fluctuation; including engagement of the heater circuit (if separate; some cars feature permanant heater circuit engagement).

If it's outside of the min/max region, it's outside of specification. If you observe that to be the case, it's time for investigation.

Again, I'm new here, but... I just thought I'd try to contribute. Nothing there is Golf specific, and if I've got anything wrong as a result, I'm happy to correct the post.

I'm still trying to learn the rules of the forum, both written and unwritten. Hopefully this post is okay for the thread.
 

shovelhd

Ready to race!
Location
Western MA
My MkV had a total water pump failure, not a slow leak, but I'm sure there were leakers, too. There's currently a class action lawsuit for MkVI cars for the same issue.
 

ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
Ya this issue goes back to at least the mk5 generation as far as I know
That would be incorrect! Much older problem that started with the MK1 :)

They initially had cast aluminum thermostat housing flanges on the older MK1s, but at some point switched to polymer. We have a '90 Cabriolet that I have sourced the 2 different aluminum flanges and 1 thermostat housing flange for to put a stop to leaks from those due to warping or cracking.

I know some of the MKV/MKVI cars had issues with water pumps and the MK4s also leak.
 

BadHombre760

Go Kart Newbie
Location
Viva Las Vegas
That would be incorrect! Much older problem that started with the MK1 :)

They initially had cast aluminum thermostat housing flanges on the older MK1s, but at some point switched to polymer. We have a '90 Cabriolet that I have sourced the 2 different aluminum flanges and 1 thermostat housing flange for to put a stop to leaks from those due to warping or cracking.

I know some of the MKV/MKVI cars had issues with water pumps and the MK4s also leak.
Re-read my post and please explain to me how it's incorrect
 

shovelhd

Ready to race!
Location
Western MA
Agree but you would think that VW would care because of all the warranty cost they have incurred.
If they fixed all of them sure, but they don't. You see it here on the forum all the time. Customer complains of coolant smell. Tech pressure tests the system, it passes, NPF. The thing finally blows and it's out of warranty. Customer pays all or part of the cost.

That's the definition of not giving a f*ck.

If the customer is smart, and takes the time to remove the belly pan and take a picture of the small leak before it blows, it gets fixed. How many owners do that? This is the cost/benefit game that they are playing.

Mine has just started to leak. The reservoir is down about 1/4". 30K miles.
 

ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
If they fixed all of them sure, but they don't. You see it here on the forum all the time. Customer complains of coolant smell. Tech pressure tests the system, it passes, NPF. The thing finally blows and it's out of warranty. Customer pays all or part of the cost.

That's the definition of not giving a f*ck.

If the customer is smart, and takes the time to remove the belly pan and take a picture of the small leak before it blows, it gets fixed. How many owners do that? This is the cost/benefit game that they are playing.

Mine has just started to leak. The reservoir is down about 1/4". 30K miles.
Yep. This just went on with my in-laws car. The dealer even acknowledged it is a common problem but they aren't seeing a leak at all. Told them to keep an eye on the tank and bring it in if it starts to drop again.
 

jimlloyd40

Autocross Newbie
Location
Phoenix
Ride
2018 SE DSG
If they fixed all of them sure, but they don't. You see it here on the forum all the time. Customer complains of coolant smell. Tech pressure tests the system, it passes, NPF. The thing finally blows and it's out of warranty. Customer pays all or part of the cost.

That's the definition of not giving a f*ck.

If the customer is smart, and takes the time to remove the belly pan and take a picture of the small leak before it blows, it gets fixed. How many owners do that? This is the cost/benefit game that they are playing.

Mine has just started to leak. The reservoir is down about 1/4". 30K miles.
The reservoir is down 1/4 of an inch in 30,000 miles. You must have a massive leak. 😂
 

LB_724

New member
Location
PGH
Edit 12/6/2019: Please file a complaint with the NHTSA for this issue using the following link, this would initiate the process for a recall.

For those interested, a thread has been started on the r/GolfGTI subreddit on Reddit.com asking for info about when your thermostat housing failed.

https://www.reddit.com/r/GolfGTI/comments/drna5m
Thought I'd put it here if folks want to contribute since so many of us have had this issue.

If you are not a Reddit user and wish to add your info, post it here I am happy to add it to the post for you. It would be tagged with your forum username and a link to your post here.
I’ll have to check my paperwork. I had mine replaced after getting the run around from the dealer back in October, and the car dead on the road the next morning from a “failed” injector. Just had oil change on Thursday and the mechanic (not dealer) said that he could smell coolant again. I don’t think that they replaced anything except the housing.
 

ReadTheBook

Drag Race Newbie
Location
Bay Area Smoke Hell
Ride
2017 GTI Sport DSG
I’ll have to check my paperwork. I had mine replaced after getting the run around from the dealer back in October, and the car dead on the road the next morning from a “failed” injector. Just had oil change on Thursday and the mechanic (not dealer) said that he could smell coolant again. I don’t think that they replaced anything except the housing.
They do the seal the housing and the union pipe, typically.
 
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