Same level of loss of coolant. Can't see a leak, though!

[Greenster]

Hi!
I got a red check engine light of: "check coolant level, stop car immediately", but then it went away, two blocks later, and then after I parked it in the garage, no leak found, but for the 2nd time in a row today, the loss of coolant was down to the same level: about 2cm above the hose that connects to the bottom of the translucent coolant reservoir. It happened twice, exactly the same!

The first time, I filled it with the proper coolant from Audi (G13, I think it said) and added some distilled water, too. I'm wondering if there is an "excess fluid overflow downpipe" or something like that, that the coolant can overflow from freely, when necessary. My older Porsche has something like that. It once had a problem like that, and a new reservoir cap fixed that problem. So I'm wondering if the reservoir cap on this car can cause the same problem? Or, what am I dealing with?
Help, please!

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[Jimingle10]

Smell coolant or get belt squeal? Might be coming from under supercharger.

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[MTL4]

First thing would be to refill it again and pressurize the system to make sure it’s holding. If it doesn’t hold you know it’s a cooling system issue and otherwise I would try a new cap then see if the problem continues. Head gasket leaks can be very tricky (they can close when cold and open when hot) but luckily this is not as common on these engines.

[Greenster]

Thank you! Yes, I too suspect that it's the Coolant Tank Cap. No squeal from the belts, but I will check under the Supercharger area, as per a YT video that I saw. Also checked oil cap earlier, no "cream" per a headgasket leak, but thank you for the reminder. Is there another area I could check to see if the headgasket has gone? It still had power, so I don't think it would be the headgasket, plus it purrs, still while revving.

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[Greenster]

I forgot to mention, no coolant smell, or visible leak, neither.

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[MTL4]

Do the system pressure test first and change the cap (if pressure holds) then see where you stand.

[Greenster]

So, yes, first thing I did was to check the coolant tank cap. It's a pressure cap, and they fail. My coolant was going down to the same exact spot each time (only twice, mind you) and so I wondered if it could be my tank cap. My Porsche 951 had a similar problem when it's coolant tank cap wouldn't seal, so the system couldn't properly reach it's specified pressure. Well, same here with my (C6) 2010 Audi A6 3.0T quattro. With the difference being that this cap has a pressure release valve in it, and at a certain point, it pops and let's out coolant to relieve the pressure. Or, in this case, if that valve fails, then it will always allow coolant to flow out through that valve until the system has come to some kind of equilibrium. The telltale sign is that the coolant will go down (leak down) to the same level and amount. In my case, it would equilize right above the bottom of the tank, 2cm above where the lower tank hose connects to the tank on the front bottom of the tank. So if you have that problem, then it could just mean that you need to replace the cap. So, check that first. Simple fix, and aftermarket caps are much cheaper than the dealer's expensive caps. $8 vs. $48!!! I got my aftermarket cap at an O'Reilly's, believe it or not!

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[Greenster]

In garage test was fine yesterday, and today I'll road/freeway test it. So hopefully there are no other leaks. If there is another leak, then I'll have my mechanic do the pressure test, and we'll see what happens then.

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[Greenster]

To add information to this thread, I will mention that there is a small channel in the coolant reservoir, that starts under the cap area, and runs down towards the engine. If you've ever added coolant without a funnel, and accidentally spilled a little bit to the outside side of the inside of the cap area, you will have heard the coolant turn to steam, hitting the engine. At first I thought that there was a crack in the tank, but then looking at it closer, and I saw the channel, and then thought to examine the inside of the cap. Sure enough, it's a pressure cap, and my guess is that this part fails rather normally.

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[11A6]

BTW there have been more than a few instances where people did report that their coolant tanks leak and since it evporates finding signs of the leak is tricky. Keep an eye out for that.

[Greenster]

Thank you! Yes, I read that too, but this tank is only two years old, but that's a good idea to check it, too.

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[Greenster]

The road test went well for a few miles, and at that point I checked the coolant level, and it was fine. However, when I returned home, the level had gone down below the low mark, but not down to the point that I had previously mentioned. So I wonder if this aftermarket cap is not correctly matched to my car, despite the website saying that it is correct for this specific car. I'm going to get a OEM cap and see if that works, though. My mechanic will also do a pressure test on Monday when I take it in.

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[rich84]

Have a look around the base of the supercharger with a torch. You can get the torch in past the nose/pulley and check for any coolant pooling around there. My PCV valve was leaking coolant externally and was pooling in this area, then sloshing over onto the belts when slowing down (causing the car to randomly lose power steering). The heater supply hose that runs from the thermostat past the supercharger to the back of the engine can also fail - either the o-ring or the flange where the o-ring sits can crack and leak. Worth replacing this pipe if you have it all apart. Most of the external coolant hoses are plastic and can leak around the unions and crack easily, especially at 10+ years old.

The PCV valve can also leak internally and mimic a head gasket issue. In fact if these engines have HG symptoms with coolant in the oil it's most likely the PCV valve and NOT the head gasket.

[Greenster]

Thank you, Rich!
Tell me more... So it could be the PCV? How can coolant get into the oil that way, albeit not much. But some did show up in my oil cap, a very, very small amount. It's also an intermittent thing. Last two drives to the store, nothing. Coolant level didn't change this time, too. I also heard that the oil coolers could also cause the same symptoms? What do you think about that? Which is more likely to be the problem? Also, my mechanic buddy suggested it could be the aluminum head having a crack in it. He also said that he thinks it's the head gasket, and to just use Blue Devil head gasket fix. I don't want to do that, as it could affect other things.
So if you were to make odds, on a 12 year old, 118,000 mile car, wouldn't a cracked aluminum head be low in probability?
Your thoughts, or anyone else's, would be appreciated.
-Thank you!

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[Greenster]

After looking on YT, I'm now wondering if the diaphragm in the PVC (PCV?) valve is the problem. No coolant over there, or under it, so not sure what to think. Could that give a coffee colored small, 50mm diameter spot under the oil cap? No where else is it found. Car runs okay, normal power, too. I know that a blown headgasket drains power from an engine, and our car doesn't seem to have that problem.

So what are your thoughts about this?

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[Greenster]

Ok, Thank you, Rich84!

I took it to VAS Motor works here in San Francisco, and Ken was really good. (The dealers had quoted mid-March before they could see it!) He pressure tested it, and sure enough, PCV Valve was the culprit. The o-rings around the perimeter had failed, letting coolant into the oil. So, he replaced the PCV Valve unit and related hoses and pipes, grommets, etc. I had the two belts from ECS Tuning, along with the rollers and tensioner, so he used them to put it all back together. So it runs great again! We rented various cars over the last few weeks, and even a brand new BMW 330i that none of my family of five thought was better than our A6, even though it has 100K miles more on it!

So I just wanted to say thank you to all the Audi people out there who helped with answers. It helped me through the process, so as to be careful and confident as to what needed to be done.

With gratitude,

Greenster
2010 C6 A6 3.0T QuattroIMG_20220122_171224.jpg

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[MTL4]

Ok, Thank you, Rich84!

I took it to VAS Motor works here in San Francisco, and Ken was really good. (The dealers had quoted mid-March before they could see it!) He pressure tested it, and sure enough, PCV Valve was the culprit. The o-rings around the perimeter had failed, letting coolant into the oil. So, he replaced the PCV Valve unit and related hoses and pipes, grommets, etc. I had the two belts from ECS Tuning, along with the rollers and tensioner, so he used them to put it all back together. So it runs great again! We rented various cars over the last few weeks, and even a brand new BMW 330i that none of my family of five thought was better than our A6, even though it has 100K miles more on it!

So I just wanted to say thank you to all the Audi people out there who helped with answers. It helped me through the process, so as to be careful and confident as to what needed to be done.

With gratitude,

Greenster

Great news on getting it fixed Greenster! I just wanted to point out this is precisely why if anyone has a mysterious coolant leak you always want to run a pressure test on the system and most of the time the culprit will become obvious right away. Sounds like it wasn't a bad fix at all and of course you found out exactly why these Audis are so coveted by their owners.

[Greenster]

Thank you!

Yes, we love our 2010 Audi A6 3.0T quattro! It has just the right amount of tech, as the newer rental cars we drove, were just a hassle. The augmented steering assist in the Bimmer was a big bummer! Felt like I was wrestling with the car sometimes. Did nothing to install confidence in driving it, so I turned all of that OFF. -Only to realize that the steering must be by wire, as there was virtually no road feedback in it. The throttle, too. Not a fan of the BMW set up. One of my brothers has an older Bimmer and I agree that his older car drives better than the newer ones! However, for me it'll always be "Porsche/Audi" in my garage! And we're going to try to see just how many more miles we can get from this car. I think the 2010's (and '09's and '11's, for that matter) with the tail lights that wrap around the back of the car, onto the side of the car, including all of the proportions of the car, make it a timeless design that I think will become a classic. It's still a beautiful car to look at! And, it's still a beautiful, fun car to drive, especially if driving is one of your passions, like mine.

Thank you again, one and all, for your help!


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[Syl Jay]

Ok, Thank you, Rich84!

I took it to VAS Motor works here in San Francisco, and Ken was really good. (The dealers had quoted mid-March before they could see it!) He pressure tested it, and sure enough, PCV Valve was the culprit. The o-rings around the perimeter had failed, letting coolant into the oil. So, he replaced the PCV Valve unit and related hoses and pipes, grommets, etc. I had the two belts from ECS Tuning, along with the rollers and tensioner, so he used them to put it all back together. So it runs great again! We rented various cars over the last few weeks, and even a brand new BMW 330i that none of my family of five thought was better than our A6, even though it has 100K miles more on it!

So I just wanted to say thank you to all the Audi people out there who helped with answers. It helped me through the process, so as to be careful and confident as to what needed to be done.

With gratitude,

Greenster
2010 C6 A6 3.0T QuattroIMG_20220122_171224.jpg

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Curiosity makes me ask.
What is the relationship between the PVC system and the cooling system? How would anything in the PVC system affect the engine coolant level?
I noticed your engine is a Turbo 3.0, so we are dealing with air vacuum AND air pressure. Still, the question remains regarding the inter-relationship between crankcase air and water cooling.

[rich84]

Curiosity makes me ask.
What is the relationship between the PVC system and the cooling system? How would anything in the PVC system affect the engine coolant level?
I noticed your engine is a Turbo 3.0, so we are dealing with air vacuum AND air pressure. Still, the question remains regarding the inter-relationship between crankcase air and water cooling.

Supercharged 3.0. The PCV sits in the valley above the crankshaft and under the supercharger and effectively is the valley cover. It has a Y shaped water gallery that seems to have some sort of heat exchanger built into it to cool the PCV gases before they recirculate into the port in the supercharger.

It can crack and leak internally or the gasket can fail internally, causing coolant to go straight into the crankcase, or it can crack/gasket can leak externally and fill the valley with coolant, which is what happened in my case.

[Greenster]

For my car, the little gaskets where the coolant enters the PCV Valve, were the culprits. Replaced the whole PCV Valve, and related parts.

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[MTL4]

Curiosity makes me ask.
What is the relationship between the PVC system and the cooling system? How would anything in the PVC system affect the engine coolant level?
I noticed your engine is a Turbo 3.0, so we are dealing with air vacuum AND air pressure. Still, the question remains regarding the inter-relationship between crankcase air and water cooling.

This is not your normal PCV system, have a look and you’ll see it’s quite substantial. As indicated there are coolant passages on the bottom of the PCV that help to cool the oil vapor. If the o-ring leaks or the part has a crack you can get coolant in your oil or an external coolant leak depending on where it is. It’s a major job to change it since you need to remove both all the fuel and intake components to get access.

Here’s a look at the part itself:
https://www.ecstuning.com/b-genuine-...m/06e103547ac/