New coolant leak after flush.. Should I be concerned?

[aslusher]

(1.8T engine- AMB)

So I did a coolant flush about 3 months ago in conjunction with repairing the much dreaded back-of-engine temperature sensor.

Went away for 2 weeks over the holidays and came back to find my fresh G13 was all over the driveway beneath the car. Further inspection revealed an expansion tank that was bone-dry, and the source of the leak somewhere around the thermostat housing. Have not been able to get in to assess more specifically what part failed (j-plug, T-stat housing, etc.). I have a new thermostat housing and J-plug on the way in any case, plan on putting it in tomorrow.

With this growing list of failing parts, I wonder if the cooling system was improperly maintained by the previous owner. Before swapping the coolant (I did a thorough flush with 4-5 gallons of distilled water), the stuff in the tank was orange. No sludge, goop or foam. My main concern is that something more serious (water pump) may be next. Just curious to see what audizine members' opinions here are.. PO's service records indicate timing belt/water pump changed approx. 20k miles ago, so in theory it should be fine. Thanks in advance for any input.

[gilber33]

It's an older car. First thing I do with the vast majority of older cars I've owned is replace the entire coolant system. Did it with my A4 that has 150k miles on it. Replaced every hose and component. Know it was either a matter of time that something started leaking and the second I replace one part and agitate the system, it will develop leaks elsewhere.

[yoitschavez]

Just did my water pump and thermostat this past week. One of the plastic "nipples" on the thermostat where a hose was plugged in completely snapped away from the housing, causing coolant to dump. The J-plug didn't appear to need to be changed, but after poking it plastic came off, so I changed it as well. Got the whole kit from ECS Tuning.

[G.AUDI]

It's an older car. First thing I do with the vast majority of older cars I've owned is replace the entire coolant system. Did it with my A4 that has 150k miles on it. Replaced every hose and component. Know it was either a matter of time that something started leaking and the second I replace one part and agitate the system, it will develop leaks elsewhere.

What exactly are the parts that consist of the entire coolant system? I know reservoir, thermostat, rear coolant flange and sensors but I was referring more to hoses. Do you happen to have a list by any chance?

[Taylor1.8t]

It's probably your coolant flange. 1.8t's are known to leak from coolant flange at the back of the engine block. I had an on-going leak recently on my A4 and it was the flange.

[aslusher]

What exactly are the parts that consist of the entire coolant system? I know reservoir, thermostat, rear coolant flange and sensors but I was referring more to hoses. Do you happen to have a list by any chance?

Here is a diagram for the AMB engine. It's a lot of stuff. I would like to also do the hoses, but unfortunately cash is tight at the moment and it's going to have to be just the thermostat housing and j-plug for me for now. Then again, I may end up doing myself a disservice in losing more fresh coolant down the road with another preventable leak. Still, most of what seems to cause leaks are the plastic housings and the o-rings that seal the sensors.

A friend of mine mentioned that he likes to smear a small amount of vaseline on the sensor o-rings before installing them. Anyone want to chime in as to whether this is a good idea, bad idea or just not worth the effort?

[Taylor1.8t]

Here is a diagram for the AMB engine. It's a lot of stuff. I would like to also do the hoses, but unfortunately cash is tight at the moment and it's going to have to be just the thermostat housing and j-plug for me for now. Then again, I may end up doing myself a disservice in losing more fresh coolant down the road with another preventable leak. Still, most of what seems to cause leaks are the plastic housings and the o-rings that seal the sensors.

A friend of mine mentioned that he likes to smear a small amount of vaseline on the sensor o-rings before installing them. Anyone want to chime in as to whether this is a good idea, bad idea or just not worth the effort?

Yes you can use vaseline, it will get the job done, but not exactly preferred/recommended...

[G.AUDI]

Cool thanks for that diagram. Yeah I pretty much replaced most of components except for a few hoses but I'm glad that its not too much more. As for OP, I know you already ordered the jplug and thermostat but I don't remember if you did the rear flange as well. I was getting the exact same thing as you where the coolant leak was all over the thermostat area and under the reservoir. I ruled out the rear flange at first because I already replaced it about a year ago. In the end, I ended up ordering the metal flange off urotuning (bit expensive) and replaced the flange and haven't had a leak since.

Sent from my A0001 using Tapatalk

[aslusher]

Cool thanks for that diagram. Yeah I pretty much replaced most of components except for a few hoses but I'm glad that its not too much more. As for OP, I know you already ordered the jplug and thermostat but I don't remember if you did the rear flange as well. I was getting the exact same thing as you where the coolant leak was all over the thermostat area and under the reservoir. I ruled out the rear flange at first because I already replaced it about a year ago. In the end, I ended up ordering the metal flange off urotuning (bit expensive) and replaced the flange and haven't had a leak since.

Sent from my A0001 using Tapatalk

Will keep an eye on the back of engine. I replaced just the O-ring and sensor there a few months back. The leak was pretty easy to observe--with a cell phone blindly taking video with phone flashlight on, I was able to clearly see it running down from the sensor/housing junction once I reviewed the video. As yet, I no longer am seeing anything back there.

Even that was a slow drip, though. In the current case, the entire reservoir drained over less than 2 weeks while sitting. I took the belly pan off and traced it upward, where I was able to see a small pool of coolant sitting on the side of the engine block. As I said, the only uncertainty is in whether the thermostat housing or the j-plug is what failed. Parts are in now, fingers crossed.

[BumblebVR6]

Always something with these cars. Just did the meta UroTuning flange as well and noticed a small coolant leak under the car from that area after it sat over the weekend at home. Nothing under when sitting at work all day yesterday. One good thing about the G12 is that it self seals small leaks. I'm going to keep an eye on it and see what happens. I'm suspecting the lower heater hose as it is original and has the original o-ring in it still. I had a spare hose when I installed the flange but decided not to replace it since the old one still looked good. Good luck with everything.

[aslusher]

I could believe that my coolant leaks were the result of age, but I am wondering if it's possible that an underlying issue is to blame.

Previous owner had a magnaflow installed, and the car has always been somewhat gurgly when reversing or starting from stop. No fluid apparent on motor mounts, but is it possible that worn mounts could have provoked the thermostat failure? Any way to test them beyond visual inspection?

[Spike00513]

It's an older car. First thing I do with the vast majority of older cars I've owned is replace the entire coolant system. Did it with my A4 that has 150k miles on it. Replaced every hose and component. Know it was either a matter of time that something started leaking and the second I replace one part and agitate the system, it will develop leaks elsewhere.

How much did that cost?

Payments on a new car, vs. a refresh? If your neighbor has a CPO C7 S6, technically your car is newer, the coolant system that is. Not the fender but that doesn't matter since yours wont rust. I'm not sure which is preferable but I think I at least see where you're coming from.
Not to suggest that car is worse. It's probably a better pricier version and faster. Much faster.

Is it not better to approach with "if it ain't broke, don't fix it" mentality, and fix one hose years later IF it leaks, versus many now?
Then again IDK how many years away classic 'parts NLA' status (URS4, etc.) is for these cars. Probably more than not.
And if you changed everything, maybe it's peace of mind for another 150k-mi/10-15yr?

I know I need to do TB service including WP, and the typical suspects are probably already leaking or will be. J-plug, rear coolant flange, thermostat. Radiator plastic end-tanks. Reservoir. CTS.
It seems people prefer metal vs. plastic where available: J-plug and flange.

Guess I need to research this further, maybe the service will at least require a ton of new replacement one-time-use clamps, maybe after cutting off the old ones.
Maybe a special crimp/pinch tool.

A friend of mine mentioned that he likes to smear a small amount of vaseline on the sensor o-rings before installing them. Anyone want to chime in as to whether this is a good idea, bad idea or just not worth the effort?

Isn't vaseline petroleum-based? Would it dissolve the same way gasoline does to a red SOLO cup, or wheel bearing grease to a rubber bushing? Then again it's use for skincare without a problem.
I'm thinking about trying Dow Corning 111, since I already have some (couple bucks for a small jar) - supposedly it was designed for uses like this.

I could believe that my coolant leaks were the result of age, but I am wondering if it's possible that an underlying issue is to blame.

Previous owner had a magnaflow installed, and the car has always been somewhat gurgly when reversing or starting from stop. No fluid apparent on motor mounts, but is it possible that worn mounts could have provoked the thermostat failure? Any way to test them beyond visual inspection?

Like shaking it apart? OG runs B5 S4 Febi mounts. Diagnosticator went with hydraulic. One things for sure, at this mileage (and age) and without proof/receipt of replacement, I know mine are original and deteriorated, which you can easily see with the snub too. The drivetrain isn't locked down.
Not sure if it will work (like with other cars) to rev it in neutral with a helper watching to see if the engine bucks around, but I'm pretty sure they're gone. Maybe I can peak underneath to see if there's purple hydraulic fluid leak/drips on them.
Then there's 034 SD, and Fluidampr. Not sure.

[aslusher]

Like shaking it apart? OG runs B5 S4 Febi mounts. Diagnosticator went with hydraulic. One things for sure, at this mileage (and age) and without proof/receipt of replacement, I know mine are original and deteriorated, which you can easily see with the snub too. The drivetrain isn't locked down.
Not sure if it will work (like with other cars) to rev it in neutral with a helper watching to see if the engine bucks around, but I'm pretty sure they're gone. Maybe I can peak underneath to see if there's purple hydraulic fluid leak/drips on them.
Then there's 034 SD, and Fluidampr. Not sure.

I am still getting familiar with this engine's setup, but the thermostat has several connections to coolant lines that I imagine could potentially tug on the plastic. At least one of those lines is a hard pipe. Maybe someone who has had component failures due to worn motor mounts would be able to enlighten us?

EDIT: just looked up cost of snub mounts. Dirt cheap--looks like I will be doing that for my peace of mind soon. Motor mounts, unless I find new evidence they are shot, will have to wait..

[Spike00513]

I am still getting familiar with this engine's setup, but the thermostat has several connections to coolant lines that I imagine could potentially tug on the plastic. At least one of those lines is a hard pipe. Maybe someone who has had component failures due to worn motor mounts would be able to enlighten us?

EDIT: just looked up cost of snub mounts. Dirt cheap--looks like I will be doing that for my peace of mind soon. Motor mounts, unless I find new evidence they are shot, will have to wait..

I heard Febi B5 S4 mounts are $30/ea.

[aslusher]

I heard Febi B5 S4 mounts are $30/ea.

Thinking of just going stock.. 11 bucks is hard to beat for OEM.

https://www.ecstuning.com/b-genuine-...unt/8e0199339/

[gilber33]

How much did that cost?

Payments on a new car, vs. a refresh?

Is it not better to approach with "if it ain't broke, don't fix it" mentality, and fix one hose years later IF it leaks, versus many now?
Then again IDK how many years away classic 'parts NLA' status (URS4, etc.) is for these cars. Probably more than not.
And if you changed everything, maybe it's peace of mind for another 150k-mi/10-15yr?


Guess I need to research this further, maybe the service will at least require a ton of new replacement one-time-use clamps, maybe after cutting off the old ones.
Maybe a special crimp/pinch tool.

idk, a few hundred bucks. I guess I should specify that I did not replace the radiator and heater core since they're not leaking. But I don't see how you could even begin to compare that to a new car payment. I have peace of mind that while I own the car I won't have to touch the vast majority of systems on it and that they will operate as they should.

IMO, the don't fix it if it ain't broke mentality is BS. Sure, wait until the day one of the hoses blows and your stranded somewhere because a 13yo hose finally gave out. With that said, I'm big on preventative maintenance. When I got my A4 I did all new suspension (control arms, sway bar links, shocks), t-belt, serp belt, water pump, thermostat, coolant flange, coolant hoses, PCV system, turbo, valve cover gasket, vac lines, check valves, and some other things I'm sure. Maybe it's overboard, but the car is extremely reliable and has never left me stranded and has zero leaks and no hiccups.

[aslusher]

Well I finally got the new thermostat in.

Once it was out, it was clear that the thermostat was fine. My theory is that, once the temp sensor o-ring on the back of the engine was replaced, the new weak point in the system (thermostat housing to block o-ring) blew. I wonder if I could've gotten away with just replacing the o-ring and not spending the 100+ bucks on the new housing and all.


I saw quite a bit of rust on the block though.. Here are some pictures. Is this normal? I didn't scrape any rust out as I didn't want to have it churning around. I did wipe the o-ring sealing surface thoroughly to remove any crumbling bits on the surface, but realize in hindsight that I may be asking for another leak relatively soon. Should be quicker to address now that I've been in there once.


Old thermostat and J-plug next to new



Rust




More Rust

in case my image links don't work

[maurizio]

ran water in her for too long?

[aslusher]

ran water in her for too long?

Something I do wonder. I did a flush a few months back, but I didn't have straight water in for more than half a day to a day. After that, the g13-water ratio may have been a bit heavy on the water side. Still, judging by the coolant's orange color when I bought the car, I think the corrosion was likely already there. Anything I can do to mitigate long-term problems at this point?

[maurizio]

Take off both coolant hard pipes; nasty crap will accumulate along their walls. Use a brush to scrub it out and prepare to me amazed at all the gunk in there..

[aslusher]

Thank you all for the help and suggestions. Unfortunately, I noticed more small puddles in the garage today. When I pulled the belly pan, I could see the drops of coolant. No leaks evident on back of engine or on any hoses I could get my hand on. I assume it is again leaking from the thermostat-engine connection. I guess I will need to address the corrosion there and/or try a fatter o-ring? Does anyone have any recommendations as for scraping or possibly reforming the metal surface with some sort compound?