Coolant reservoir empty :(

A6 All/ S6 All
#1

So i was driving close by home picking up some food and start hearing some beeps and I see this red thermometer flashing, it says coolant something something, I couldn’t catch it fully since i was on the road, am looking at the temperature gauge and that still seems to be under normal operating temperature, so I drive another 5-8 minutes and reach home, pop the hood up and look to see the coolant is close to empty. I can hear some hissing (probably some coolant hitting some hot engine parts or exhaust.

Have the following questions.

  1. Foremost, any chance i could have damaged the engine? I didn’t see the temperature gauge climb higher then normal operating temp and there is still some coolant albeit close to empty in the coolant reservoir.

  2. How do i go about diagnosing this? I mean I have lost a lot of coolant and given the hissing sound, can i assume that the engine is not filled with coolant? anyways I am rambling… how would one go about diagnosing this issue.

  3. In order to get on the ramps, I need to turn the engine on again, I can fill up the coolant reservoir and drive it up the ramps, this should be ok right?

Appreciate all the help i can get guys.

#2

  1. If the reservoir had fluid still in it that is a good thing. Depending on now long you drove for it’s not very likely that you did any damage. Also the hearing hissing is a good sign that there was still some pressure in the system, again a good sign.

  2. It’s unlikely that the engine is without coolant. I would need to see more to get a better idea on what happened. with the motor cold you can start by checking the rad hoses to see if they still have coolant and they most likely are going to still have coolant. Inspect the lines coming and going from the reservoir. Chances are the plastic Y fitting cracked or the actual coolant tank reservoir is cracked. It’s a typical issue that will spew out coolant everywhere. So, I would suggest doing a general inspection on all of the visible coolant lines and look for signs of coolant both standing and otherwise.

From there if you didn’t find the definitive source of the issue, I would top off the coolant reservoir and then start the car. leave the hood popped and wait for a few min. The system will pressurize and you’ll start to see more of what is going on.

  1. This backs up to the above point. You can star the car and run it for a few min without coolant. Don’t go trying to drive anywhere but to start and move the car a very short distance will be fine. Just be mindful that there is a possible open coolant leak in the system and you could leak coolant.

Let us know how it goes.

#3

Thanks for the advice count, unfortunately in my haste\panic I already topped the
coolant reservoir so I cant really perform some of the diagnosis you suggested however
I observed the coolant hoses at the top left and the top right going into the radiator,
they seem to have no sign of leakage or any pink substrate.

I then pulled out the front noise insulation at the bottom front of the car and took a look
from below and I can see signs of leakage on the passenger side.

front passener under car
front passener under car3024×4032 2.26 MB
.

If you look closely you can see drops of coolant milling under the nut in the picture, given this it does seem fair to suspect the reservoir or thereabouts or something on the passenger side, I cant really make out if the coolant reservoir is leaking or the plastic Y fitting (where is this plastic Y fitting? ) since its a little hard to look underneath there, I ordered a bore scope that my friend suggested and possibly
that should help look underneath the coolant reservoir.

#4

Passenger side? You may have a cracked coolant reservoir. Mine would not leak when cold so I did not notice a leak. However, when warm coolant would just disappear and my coolant light would come on every day. It ended up being a hairline crack in the reservoir from heat cycling. I’m 50k miles, I’ve had two crack now. I’m on my 3rd one. Seems to be a semi common problem for some. I’ll try to find the picture and add it here.

#5

I see, didn’t realize these blow up so often. I went ahead and ordered a new reservoir from JHM. Are there instructions on how to replace the reservoir in the manual? or if any one has a general set of steps to follow? Does one need to flush out the coolant completely in order to replace the reservoir?

#6

Well, it never happened on my S6. It’s now at 128k miles (207k km).

#7

I looked a little more today and used the bore=scope to look on the passenger side, I couldn’t see any active leak but definitely continued to see traces of coolant around the passenger side. I started it by using bore-scope with the engine turned off and then turned on the engine as well, however the worrying thing i noticed is that after a few minutes of the engine running, i started hearing a shrill whistling sound, I checked to see if the coolant light or any check engine light had come on but that was not the case.

Is it possible that this is because of an overheated engine?

I have a video with the whistling sound however I cant seem to upload that video, do folks know if there is a way?

#8

As mentioned by count and raz it’s probably the coolant res.

The whistling noise is pressure leaking out of the system. The coolant system pressurizes. That is in part how the coolant makes its way around. So don’t worry about the noise that should be expected. What you should do is crank on the heat in the car then let the car idle.

Once you hear the noise try to locate the noise location exactly. Then wait and you should start to see a mist coming from that location as the water pump kicks on to move the water around. At that point you should start to see more of what is going on . Just make sure to peak in on the dash to make sure the gauge on the dash stays in check.

#9

I see, so if I understand you correctly the noise is probably where the coolant is leaking from? Also what is the significance of turning on the heater to high? what does this do in this context?

#10

The hissing should be air leaking past whatever spot the break is in the line hose etc.

Running the heat just make sure that if the system starts moving that its pulling heat out of the system by running it though the heater unit.

#11

I still haven’t gotten enough time to actually find the source of the leak due to inclement weather here in the pacific northwest but I am hoping to get it to this weekend. I was in the interim going through the various components of the cooling system from the Bentley manual and had a couple of questions around this.

  1. What is the difference between a coolant line and a coolant pipe as it reads in the manual ?

  2. When the manual mentions left coolant pipe, is this on the driver side or the passenger side. I am guessing this is on the driver side but want to make sure.

  3. I couldn’t be sure but it seemed like the noise was coming from the driver side. now if the leak is on say the left coolant line, would i be able to even see the coolant leaking out since its underneath the engine ? also if this is indeed the case, does this mean i need to pull the engine out?

#12

I would have to see more of the meaning but I think the only coolant pipes are on the passenger side. The driver side between the heads and the frame rail has no coolant line that isn’t included in the water pump.

The main coolant lines or pipes are on the passenger side coming from the rad. The line in the back of the block and the fittings on the back of the heads. There is the water pump pick up and soft hoses there.

Most of the coolant leaks I have seen tend to be in the area of the coolant tank or behind the heads.

#13

Ok so I think I am much closer to figuring this out and you guys seem to have been right all along.

I started by just observing if there were any puddles of coolant under the car and sure enough under the reservoir i saw another puddle on the ground, so i wiped that clean and started up the car and let it run for some time, the sound I mentioned appeared after a while and just went away after a bit. I let the engine get to operating temps and then revved the engine a little to 2- 3 k RPM, i went back under the car and sure enough another puddle of coolant right in front of the wheel well.

Leak1
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I then switched the car off and pulled out the right (passenger side) air filter housing in order to get a good look and put the bore-scope in there and sure enough could see coolant starting to mill right above the wheel well, very close to the reservoir.

Leak2
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This happens to be right under there below the red sqaure highlighted.

Leak3
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At this point I am close to certain that the leak is from the reservoir since it would be very hard for coolant to get there due to a leakage anywhere other than the reservoir. What do you guys think?
is it safe to assume this is the reservoir leaking and go ahead and replace it?

Also how does one replace the reservoir ? I just cant seem to find instructions for this in the bentley manual… :frowning:

#14

So just looking at the reservoir assembly it looks like there are just a couple of torx screws holding the reservoir down, the questions I have around this is

  1. What is the ideal process for replacing the reservoir? do I perform a coolant flush completely? or can I just pump out coolant from the reservoir and simply replace the reservoir?

  2. What happens if air gets into the coolant lines? is that bad? I saw some video about replacing coolant on an A4 where the poster simply let the engine run with the coolant tank cap off to let the air bubbles out of the system.

#15

When I replaced it I just drained the tank, then after that filled the tank back up with a funnel, overfilled the funnel and let it run like that until the bubbles stopped. Idk if there’s a certain procedure for it but that was about a year ago and I haven’t had any issues.

#16

Got it, thanks. Am going to do the same - will use a transfer pump that I got from harbor freight to empty out the reservoir before removing it, am still waiting on the replacement reservoir which should be here by the end of the month hopefully.

#17

Yeah it’s super easy to swap. The thing you have to be careful of is the plastic Y piece you will see it . It breaks for a lot of people. So be careful. But overall its not a hard job.

Since your going to be swapping out the tank. Pull the screws out of the mounting points for the tank and lift it out of place. Now with the tank out start the car and look at the bottom of the tank see if you can see the tank leaking with it lifted up. just to make sure

#18

So I followed a variation of your advice and basically pulled out the air filter housing and connected the filter to the hose outside of the enclosure and then started up and ran the car to get a better look and found that the reservoir just did not seem to be leaking.

Leak4
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I then realized why coolant had pooled down there, the reservoir itself has an overflow mechanism around the opening where in the excess coolant flows down a stem. In most likelihood when I refilled the coolant, the coolant had probably overflown down that and finally milled right underneath the coolant tank.

InkedLeak5_LI
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the sucky part is now I am back to square one. I am still confused how I could have lost so much coolant.

I did see this T-junction hose near the front passenger side that did show some signs of leakage, but am not sure if this could have been the source of such a big leak? Am going to let the start it up today and let the engine run for a longer period of time this time and see if i loose any coolant.

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Anyone know what this part or hose is called?

1 Like
#19

First off. PICTURES ARE SO HELPFUL…

If your hearing hissing. There is a leak and pressure is getting out. From the sound of it… its coming from the coolant system. The coolant T is showing signs of leaking or at the very least coolant getting on to the T. But since they tend to crack and leak I would say that might be part of the issue.

You have to let the system pressure build up to really know what is going on… BUT if you let the system pressure build up there is a chance that hot coolant can be spraying or leaking out. So be careful but if you track down the hissing noise you should be one step closer to the issue.

#20

Thanks Justin.

I plan on doing a more thorough inspection this week by adding some more gas and running the engine for an extended period of time and try and get to the source of the whistle, the issue has been that it is not so straightforward to identify the source of the sound over the rest of the engine sound but I am going to give it a real good try this week.

Any idea what the part number for the coolant T is? I have been searching on Audi parts under coolant and hoses and am unsure which part this really is. (https://www.audiusaparts.com/auto-parts/2008/audi/s6/base-trim/5-2l-v10-gas-engine/cooling-system-cat/hoses-and-lines-scat) .