Coolant Loss Mystery

Farmboy

Veteran Member
Joined
Jul 29, 1999
Location
Bloomington (Minneapolis), MN, USA
TDI
'15 Golf SE TDI 6spd 109k miles; '00 A4 NB 5spd 216k; '96 B4 Passat Sedan 220k
Yep. Coolant loss mystery.

Car purchased new August 2014.

2015 Golf TDI SE, 6 speed manual transmission.

I have topped off for a nag light (low coolant light) 6 times in roughly 8 years & 93k miles.

1 - 29,658 - 07/16/2016
2 - 34,480 - 12/15/2016
3 - 75,547 - 02/08/2021
4 - 92,799 - 06/25/2022
5 - 92,870 - 07/04/0222
6 - 93,186 - 07/23/2022
7 - 93,305 - 08/10/2022 (preventive fill, no nag light)

Never white or foam in oil. No obvious - to me - indication of coolant overflow at the plastic reservoir. Currently some white specking on the top of the plastic sphere that I suspect is due to my micro-spills & splashes while pouring. No obviously enormous - to me - pressure release opening the tank cap. Nothing else jumping out at me as a cause for concern or a way to narrow down my mystery loss.

At nag light #5 there was a tiny puddle on the ground in the garage under the right rear corner of the bottom engine cover.

I put the car up on ramps, pulled the bottom cover, got a bright light, and looked all over for witness lines showing a coolant leak path. There was no - to me - clear indication of where coolant had come from.

At nag light #6, I filled either all the way to the MAX or at least to a point roughly 1/2 way from MIN to MAX, didn't record properly in my log, don't recall for sure. I simply recall feeling frustrated at my inability to pinpoint the leak source and belief that "overfilling" was a livable trade-off until I've resolved the problem.

Today, top off #7, rather than wait for the nag light again, I filled to MAX as tank was at MIN. The car is mainly driven by my wife, a school teacher, so it's easy to let it mostly sit idle during the summer, as other projects are consuming time. Fall is coming, though, and my hope that the cause of this mystery coolant loss will make itself safely obvious is diminishing.

The only other weird coolant system thing that has ever happened is that the lower radiator hose popped off during my wife's commute shortly after the 10k complimentary dealer oil/filter change. Engine was shut down prior to catastrophic destruction, car was towed/flatbedded to the dealer, dealt with, and all subsequent oil changes have been by my hand.

If Bentley is available (print, CD, or whatever they sell now), I haven't purchased one yet, which means much of the engine & coolant system detail is still a mystery to me, if it's even well described in the Bentley, should it exist. I have looked through other threads here, and don't feel I've found any clear connection to any other reported issue. Could easily have missed something. If so, hopefully someone will gently and kindly point me in the right direction.

Based on my reading here, absent obvious alternatives, I'm giving serious thought to simply doing the timing belt, water pump, etc. now and see if maybe the WP is the culprit or something in that area, a connection, whatever.

My major question, after all that: Does anyone know this engine well enough to guess the most likely mystery loss point? Is the best guess water pump?

My minor question, go with OEM water pump or with a non-solenoid pump?

Other than that, anyone have any thoughts about anything I'm overlooking, should be planning to do to resolve this problem, etc.?


Until now this car has been a dream, now I'm starting to worry about the complexity & cost as it ages and truly requires attention, as compared to previous vehicles I've maintained and repaired for myself.


Thanks in advance
 

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
Well you are close to TB time/mileage limits so I would more than likely just do that and get it over with. Water pumps have seemed to be an issue at times with these cars. My daughters 2015 Passat had to have a TB job because of this. A complete job and kit by someone who knows what they are doing. In warranty I would go with what it came with, just to rule out any possible issues there, out of warranty non-solenoid pump seems to be recommended now.
 

hskrdu

Top Post Dawg
Joined
Oct 17, 2003
Location
Maryland and New England
TDI
2003 Golf GLS 4D 5M, 2015 GSW SE 6M
I found all the repair modules as PDFs online, I think a member here, or maybe at the UK GolfMK7 forums posted them. If you can't find them, pm me and I can email them to you. I believe you can also get them from Erwin one-day subscription? Otherwise I would echo what Lightflyer said, our 2015s seem to need a little coolant more often than the MkIVs, and the WP is a known leak source. Our 2015's will likely get a non-variable WP at the TB service.
 

GolfSW98

Veteran Member
Joined
Feb 8, 2021
Location
Texas
TDI
2015 GSW TDI
Check and see if your silica packet is intact, found at bottom of the clear reservoir.
 

15TDICommuter

Veteran Member
Joined
Jan 6, 2019
Location
South Florida
TDI
2015 GSW
I've run into similar issues with my 15, although not to the point where a light was placed on the dash. I think between the overly complex cooling system with its various smaller circuits, loss can be anywhere. Like others mentioned, might be worth having a professional complete the TB and have them do a deeper dive as they will have the car torn down a bit. While the car keeps me on my toes with regard to coolant, I have yet to find anything that leads me to believe that its something I can fix.
 

Wasserpest

Veteran Member
Joined
Nov 17, 2004
Location
Monterey, CA
TDI
'10 Jetta SW 6MT, '15 Jetta DSG
To add another datapoint, with my 15 Jetta, after years of reliable service I now experience the loss of coolant, conveniently announced by the low coolant light. When it happened the first time, I had the coolant flushed (first time so I guess it was about time).

Now it has happened another couple of times. No obvious leaks, puddles, or traces of coolant overflowing anywhere. Hope it is not something huge like a head gasket, but would like to get it addressed as my wife drives that car and she is of the "let's see if it goes away by itself" crowd.
 

Farmboy

Veteran Member
Joined
Jul 29, 1999
Location
Bloomington (Minneapolis), MN, USA
TDI
'15 Golf SE TDI 6spd 109k miles; '00 A4 NB 5spd 216k; '96 B4 Passat Sedan 220k
Thanks to all who have viewed my post/thread and especially those that have offered feedback.

I've started a timing belt TB/water pump WP/kit change (by my hand). Been taking pics, am considering putting together a PDF for others' reference, as I may not be the only one well served by a 100% model specific PDF.

So. I'm curious - anyone interested in a USA (NA?) 2015 Golf CRUA EA288 specific timing belt procedure PDF write up?
(Did I miss a model specific PDF that's already out there? It's not too late for me to benefit from someone else's documentation skills)

Anyone know how well a Golf CRUA EA288 PDF will match up to the USA (NA?) 2015 Jetta/Passat/CVCA EA288 application?
Just curious if anyone knows how likely it will be a less than 100% match, since I"m not enough of a VW/TDI geek to know.

When I have enough of a time slice, I'll respond to comments as appropriate, for now I'm hard press to get my 5 hour (less?) timing belt kit change done in 5 days due to other life tasks that can't go ignored for very long, along with the fact that I'm doing my research on the fly rather than in advance.
 

Jbwoo

Well-known member
Joined
Oct 28, 2018
Location
Kingston WA
TDI
15 GSW 06 Jetta BRM
Do your proper homework. There is a different crank alignment tool than all other previous models. I can do the belt in probably less than 3 hours, and I’ve done 3 of them. Doesn’t include the other service things that are usually done, DSG, engine oil, or fuel filter. Do the tensioner and belt while you are there.
 

BT715

New member
Joined
Jan 17, 2024
Location
Missouri
TDI
2015 GSW SEL
Did you ever find a solution to your problem, or a problem to solve? We've had our golf since new and it's been doing the same thing for the past few years. Very slow disappearance of coolant as evidenced by the reservoir going low over time. The problem gradually got worse until we had a water pump failure in the summer of '23 at 145,000 miles. We hoped that was the problem but it wasn't. After replacing pump & timing belt and doing a flush with all new VW coolant, our situation didn't change just continued to gradually get worse. 10,000 miles later by December we were topping it off at least weekly and still unable to find anything myself we finally took it to the dealership. They claimed to have done a pressure test and couldn't find a problem so we took it to Oilhammer. He found coolant getting into cylinder 3 and recommend we take it back to the dealership as there is a very good chance it should still be covered under the extended emission warranty. So that's where it's at right now. I'll update as we learn more.
 

schwinn guy

Active member
Joined
Dec 27, 2008
Location
Chicago 'burbs
TDI
2001 Golf GL 5 speed
Good luck.
I saw your post on that thread and have a similar issue going on.
2-3 times my coolant level got low and my dash light came on and I topped it off. No sign of coolant loss. That hasn't happened for over a month now. I did have a bad burning electrical smell in the engine compartment for a day or two which went away to be followed up right away with an overheating problem. I've read a lot of the threads that I could find on the issue, non with the exact circumstances as I'm having, so it's off to the dealership for them to diagnose and fix under warranty. ( 2015 GSW with 72k miles ) Thanks to Oilhammer for his input on my issue.
 

Farmboy

Veteran Member
Joined
Jul 29, 1999
Location
Bloomington (Minneapolis), MN, USA
TDI
'15 Golf SE TDI 6spd 109k miles; '00 A4 NB 5spd 216k; '96 B4 Passat Sedan 220k
Wow, time flies and I missed the replies here.

BT715 - Premature bearing failure in water pump creating a weep path along shaft. IMHO, likely caused by dealer work at 10k which starved mechanical pump of needed lubrication, though it took some time and miles to finish the job.

schwinn guy - if nothing else, perhaps doing an early TB kit change like I did might help you eliminate possible root causes. Recommend the non-solenoid replacement pump.
 
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