potential coolant leak

[Wiredin]

My coolant overflow tank is steadily dropping. After I let it sit for an hour I go check it and before it was just above min, now this week its about an inch and a half below min. I went and grabbed some G12+ to top it up. Checking what I can see without a hoist I'm not seeing any active leaks, and I'm guessing I wouldn't as it's a pretty minimal amount (maybe 400ml?) thats leaked out. I'm guessing thermo housing? The waterpump and stat were changed 2 months ago.

[jwallace0988]

In my past experience... On my 2012 gti - It was related to the water pump that went bad prematurely. After I replaced that, I still noticed that coolant would slowly have to be added over time. They techs said that it is common... Since the engine consumes the coolant for lubrication purposes. Something along those lines, good luck tho!


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[Dr GP]

Since you just had the WP and T Stat replaced, there probably was some residual air in the system. It will take a little time for it to work itself out of the system.

[rwtzero]

I had my overflow tank replaced recently, they pressure tested it for hours afterwards at temp. I STILL need to fill mine once a month and have NO IDEA where its all going! I only fill it when its hot, I fill it to under the max line, within two weeks, its at the low marker at temp.

no idea! blow-by? where else would it go?

[EHesh14]

I wouldn't worry about it if you already did the metal pump and thermostat. I've noticed that I need to add a bit every so often during the colder months and I made sure there wasn't any leaking anywhere. My ams pump was leaking a bit, but somehow it's not anymore.

Stated above there is probably some air bubbles in the system that's causing this.

[xpoweruk]

Just for reference

When the engine is cold it should be between the “MIN” and “MAX” marks. When the engine is hot it may be slightly above the “MAX” mark.

[rwtzero]

How would you know if the pump was bad? 2012 S4

today: Driving around during lunch time. I watch my coolant temps all the time on my P3 gage. The temps are usually between 200-212F. Parked the car and the coolant was POORING out of the overflow tank! I start the car again check the temperature and its 227, within 3 minutes or less, the coolant temps were back down to 190 and the coolant was well below the low line.

pump? Thermostat?

Also, the overflow tank low and max marks are hot levels, why would I want it between that when cold? It seems that would surely overflow at all times if I kept it like that.

[Wiredin]

thanks for the info

[xpoweruk]

I'd fill the coolant to half way between min & max when cold
Have you tried a new expansion tank cap?It could be faulty causing the coolant to overflow at too low a pressure

[Wiredin]

I'd fill the coolant to half way between min & max when cold
Have you tried a new expansion tank cap?It could be faulty causing the coolant to overflow at too low a pressure

I put it about half way on saturday. it seems to be sitting pretty. took a full L of mix to get it there.

[rwtzero]

I have a brand new overflow tank. I'm not sure if that comes with the cap or not, but I do know that the coolant was clearly boiling and exiting the overflow.

[mgaman]

FWIW I just had my car in for service and to check a coolant leak, I was having the same issue. They found a hose on the bottom somewhere, don't have the notes in front of me otherwise I would specify where, but it had a small leak and needed to be replaced.

[rwtzero]

FWIW I just had my car in for service and to check a coolant leak, I was having the same issue. They found a hose on the bottom somewhere, don't have the notes in front of me otherwise I would specify where, but it had a small leak and needed to be replaced.


Thank you! I think they mentioned that to me at some point too, but then when they pressure tested it..... no issues. I will stop back and have them take another look.

Although, this doesn't explain my boiling over issue. :/

[Wiredin]

dropped below the min mark again when I checked this am (cold).... she's going to the shop tomorrow for a pressure test (and brakes, and springs... and rear diff leak....)

[rwtzero]

I think you need to check it while its hot, not cold. those marks are the hot level from what the Audi techs told me.

[infinkc]

My hose coming off the bottom of the coolant tank was leaking very slowly. I found when doing my spark plugs, the movement of the tank disrupted the seal.

[timzcat]

I have a brand new overflow tank. I'm not sure if that comes with the cap or not, but I do know that the coolant was clearly boiling and exiting the overflow.

I'd be thinking a bad cap. If while driving you were at 212 but had flow and possibly some pressure in the system then you would not be boiling over. As soon as you stopped, the pressure was lost from the system and the boiling point was reached and therefore it started to boilover, inexplicably. Restarting the car showed 227 which is still not boiling point for a system that would still have been under pressure from just running.

Obviously anything that is not maintaining pressure is going to be your problem, I say cap because if you had it pressure tested then they removed the cap to do so. I would definitely have the cap tested

[rwtzero]

Thank you!

[rwtzero]

I'd be thinking a bad cap. If while driving you were at 212 but had flow and possibly some pressure in the system then you would not be boiling over. As soon as you stopped, the pressure was lost from the system and the boiling point was reached and therefore it started to boilover, inexplicably. Restarting the car showed 227 which is still not boiling point for a system that would still have been under pressure from just running.

Obviously anything that is not maintaining pressure is going to be your problem, I say cap because if you had it pressure tested then they removed the cap to do so. I would definitely have the cap tested


Found one local... $9.20 at German Auto Parts!

[Wiredin]

just heard from the shop. thermostat leak

[rwtzero]

oh! Let us know what thats going to cost!

My overflow cap O-Ring was TOAST! replaced the cap, hopefully that was half of my problem.

[Wiredin]

oh! Let us know what thats going to cost!

dealership gave me a free extended warranty trial when I bought the car. 3 months and 5,000km.

Tech also found the read differential leaking at both output shaft seals.



The plus side is, I'm getting brakes and lowering springs done (I'm second guessing how low I bought though...) and the tech is telling me that if everything gets approved it will save me a ton of labor on my brakes/springs!