Coolant loss after water pump & thermostat replacement?

[Mk_GTI]

2018 Golf R with 32k miles. Water pump and thermostat replaced under warranty three months and 3k miles ago. Last weekend, I took a corner rather fast in race mode and got the LOW COOLANT warning. Restarted the car and it hasn't come back on since, but the coolant level is quite low again. Filled it up to the mid-level with distilled water after taking this photo.

Any ideas what might cause this? No other leaks as far as I can see.

 

[kevinkar]

That's pretty freaking low and would indicate to me there's a leak. Time to get some dye into the system and check. Or have another pressure test done.

I've also had radiators and the coolant systems serviced in my past cars and plenty of times the mechanics failed to "burp" the system and left air bubbles in which resulted in almost immediate "low coolant" lights and a less than full reservoir which could have happened here but that usually happens right away as soon as the thermostat opens and coolant starts circulating, not after 3 months.

What is the warranty on the service you got? Hopefully not less than 3 months/3k miles as this is a good reason to bring it back for free.

 

[aloha_from_bradley]

I've just come to terms with the fact that the MK7 loves to drink coolant. I had my water pump / thermo housing replaced earlier this year and still lose coolant slowly. The first two times I had the car pressure tested there was no drop in PSI. The tech had to leave the tester on the car after a cold start for a full hour before they were able to detect a leak.

Lately I've been smelling coolant after longer drives again, and I see the level drop on the overflow as well. I fill up with distilled water like you mentioned and just keep an eye on it to make sure it doesn't get too crazy. I'll be having another pressure test done on my next oil change, but I don't think my issue is with the water pump / housing. My thoughts are that it's just the de facto response from the dealership because of a part that known to fail. I think my leak is likely coming from a different source that hasn't been found.

Like kavinkar said, there is a chance the system wasn't blead properly when it was refilled with coolant. Are you smelling coolant burning off?

 

[anotero]

Check the nipple adapter for the coolant line on the rear part of the engine block. It's plastic and breaks over time, causing leaks.