Coolant System Problems

[thebatmanfan]

Hello all! Been here a few years as a lurker and this is my first post. I have used the forums to do some maintenance on my 2010 S4 in the past, but now I am stuck on my most recent maintenance project and need some help!

I have done all the work to replace the Water Pump, Thermostat, and PCV Valve (supercharger off and all). I am trying to vacuum test my coolant system, but I am experiencing a few problems:

1. The coolant system does not generate a vacuum of any kind (except enough to see some undrained coolant fill the reservoir some from the bottom). The needle on the gauge does not move on the vacuum filler. I have tested the vacuum filler, and it does operate correctly. Obviously I'm sucking in air from some hole somewhere. When I open the pet cock drain valve, while trying to pull a vacuum, it drains a little coolant.

2. Seeing as there is residual coolant in the system (see #1), I am having problems getting anymore to drain out, save from a slow drip out of the pet cock drain. I have disconnected the hoses by the oil cooler on the driver's side and drained most of it. Are there other points I should try?

Here are my thoughts: Problem number 1 with the evidence of the pet cock valve still draining (albeit slowly), makes me think there is a hole (maybe a rather large one) somewhere in the system between the coolant reservoir cap and the pet cock valve. This leads me to believe that maybe I have left a hose disconnected, but I cannot find one. Possibly a hole in the reservoir or the radiator? I am leaving the pet cock valve open over night to hopefully help problem #2.

What is my next play here? There is no (or little rather) coolant in the car, not enough to start it or pressurize. Do I fill it and run it for a few minutes and then try to manually pressurize the system and look for leaks? Would a pressure test kit from a local auto parts store work on this car? I can't find what pressure the system is rated for. Any clues on where to look for a leak based on the info I have given?

I am almost at a loss. I feel like I have put a lot of work in this project just to have to take it to the shop anyways. Any kind help is very much appreciated.

[SwankPeRFection]

You sure you seated everything properly in terms of the thermostat and PCV valve? Also, the heater core pipe that runs from the thermostat housing to the back of the engine can sometimes be a bitch to get out or seat back in since it clocks as it goes in. The other thing is the front water pipe nipple up top… make sure you didn’t snap that off by chance. If everything is back together properly only other place you’d have a coolant leak is your intercooler cores in the supercharger. If you’re on the originals, I’m surprised you didn’t see evidence of them leaking when you took the charger off. You can rule them out by just looping the front pipe hoses together with a two sided barb fitting to completely by pass them. If it holds vacuum then, you’ve got your answer. If it doesn’t, you’re either not using the tools correctly or you’ve got a leak somewhere else. You can always fill it up with coolant and search for leaks that way.

[thebatmanfan]

Funny you should mention the front water pipe nipple up top...I in fact did snap this off trying to get the serpentine belt back on. I tapped in a brass nipple and used marine JB Weld to seal it off. It's not the problem.

I am pretty sure everything is seated properly when I installed the PCV valve, thermostat, and water pump. I could go back and check. Using a cheap harbor freight torque wrench, so it might not be exactly correct. I will try the test you mentioned for the intercooler cores in the supercharger first. Then disassemble and reseat everything.

I am aware of the difficulty the heater core pipe provides. This was another area of concern for me during reinstall. Can you clarify what you mean by "clocks as it goes in"? When I put everything back together, it felt like this was just sitting in the thermostat housing and not sealed off.

I will probably end up cracking my supercharger bleeder screws and filling it up if all else fails.

Thanks so much for the quick reply!

[SwankPeRFection]

If you didn’t have difficulty putting the screw back in that holds the heater pipe in place on the back side of the motor, then it should be properly seated. You’d have to have a pretty big leak (obvious something wasn’t seated right) for vacuum to not pull. Either that or that tool you’re using to do this is junk. Honestly, I’ve never used vacuum to pull in coolant on several refills now and never had any problems. Contrary to belief, our coolant system will still fill up all the way even if you do it the old fashioned way. There’s no magic involved.

[thebatmanfan]

We all know there is not much room back there, but once I got the right tool that would fit, I had no problem. Does the heater pipe snap or pop into the thermostat housing? It's an all plastic connection and doesn't seal like a hose would on a plastic nipple. It just sort of sits in there and the screw provides enough force forward to keep it seated?

The tool could be junk, and I may not be getting a great seal on the coolant tank. I just know it pulls leftover coolant into the tank from the bottom but doesn't move the needle.

Looking it over real good for forgotten hoses and then filling her up and seeing what happens seems like the best thing to do. Maybe take the SC off one more time to torque bolts again and check that heater core pipe first though.

[SwankPeRFection]

It’s your call if you wanna take it all apart again. I know I’d hate to do it if it was all fine and it’s just a junk tool. Maybe test the tool’s ability to pull vacuum with a ballon on it’s fitting or something that can seal properly. That heater pipe has this L shaped part that comes off of it on the back of the engine which kind of helps twist it off and back on. It’s been a while since I’ve had to mess with it, but I know it was a bit of a PITA to pull out because it doesn’t just come straight out. No room to wiggle. If I remember correctly that tab helps to shift it and come out and also to go back in. I don’t believe the screw will go in all the way properly if the loop for it on the pipe wasn’t completely flush against the block, but it may be hard to see if you had difficulty getting back there.

[thebatmanfan]

I did test the vacuum filler and it does work. It may be a different problem with it when hooking it up to my coolant reservoir. Maybe not getting a good deal or something. I'll try something different tomorrow.

I went and borrowed a couple of better torque wrenches and am going to try reseating everything, double check all connections and hoses and vacuum test again. If it still doesn't pull a vacuum I'm going to fill it up to see if I can find the leak. Will update with what I find.

[Nelson G]

I just did the same thing replaced the thermostat and water pump and put it together and the vacuum tool did not work. I purchased a radiator pressure tester (https://www.harborfreight.com/radiat...kit-63862.html) and found that the cross-over pipe was leaking. I had replaced the gaskets, but the pipe had a small crack at the bottom where the gasket went. I took everything off and replaced the pipe and the vacuum system worked and no more leaks.

[thebatmanfan]

Nelson, did your vacuum filler pull any sort of readable vacuum with the crack in the crossover pipe?

[Nelson G]

yes, but it was low and the upper radiator hose did not collapse as it should. I made the mistake of filling the system and then the leak became evident. The problem with the vacuum is that there is a lot of noise you can't hear the sound of the leak because your compressor is running. When I purchased the radiator leak tester I could hear it and then knew it was the cross-over pipe as I could see the coolant running out. Remember there is still a lot of coolant in the system so you don't have to have full to pressurize it.

As I said earlier the crack in the pipe was small but once I replaced the gasket the area became more exposed. I took the supercharger off twice just to do the job right. The hardest part was separating the cross-over pipe from the upper radiator hose. Once I got it off-putting it back together was a struggle. I found somewhere an owner put a little bit of oil on the gasket and the connection slipped together. I tried it and it worked. I know oil and coolant but it is little you put on, its like when you put some oil on an oil filter before you spin it back on.
I hope this helps

[thebatmanfan]

Yes it does help. Thank you both. You have both helped. I will continue to look for my problem and report back. Going to make a trip to HF to pick up that radiator pressure test kit. Been looking at that off and on for the past week.

[A4Qwattro]

yes, but it was low and the upper radiator hose did not collapse as it should. I made the mistake of filling the system and then the leak became evident. The problem with the vacuum is that there is a lot of noise you can't hear the sound of the leak because your compressor is running. When I purchased the radiator leak tester I could hear it and then knew it was the cross-over pipe as I could see the coolant running out. Remember there is still a lot of coolant in the system so you don't have to have full to pressurize it.

As I said earlier the crack in the pipe was small but once I replaced the gasket the area became more exposed. I took the supercharger off twice just to do the job right. The hardest part was separating the cross-over pipe from the upper radiator hose. Once I got it off-putting it back together was a struggle. I found somewhere an owner put a little bit of oil on the gasket and the connection slipped together. I tried it and it worked. I know oil and coolant but it is little you put on, its like when you put some oil on an oil filter before you spin it back on.
I hope this helps

I hope you may never have to do it again, but for thebatmanfan, you can also put coolant on the gasket. The coolant itself will act like lube to get it on easier.

[thebatmanfan]

I hope you may never have to do it again, but for thebatmanfan, you can also put coolant on the gasket. The coolant itself will act like lube to get it on easier.

I have some Molykote I have been using. Works well for lubricating o-rings and gaskets. Will try the coolant though if it gives me too much trouble.

[carguy19]

the pet cock drain valve

Petcock is one word. You probably want to make sure you're clear with that word choice unless you have a fondness for roosters or ummm ??? .... I'm just gonna stop there. LOL

In all seriousness, are you certain that you attached and tightened all the coolant lines and didnt double gasket the water pump or thermostat? It has to be a really big opening to not have any vacuum at all in the system. Even if a clamp was loose, or had a slow leak you would have a few PSI of vacuum.

[thebatmanfan]

Okay carguy we all know what's on your mind....lol.

I think I actually found my issue. I left out the screw that secures the front coolant return (crossover) pipe to the thermostat housing. I figure if I can wiggle it in and out with my fingers that 10 or 15 psi of air can leak through it. Problem now is ... I can't find that dern screw. Anyone got a pic of the whole thing or a part number?

[Nelson G]

Look at this write-up and the Coolant Pipe runs across the front of the engine 4 bolts- T30 fasteners torque to 9Nm one T25 fastener

https://blog.fcpeuro.com/how-to-repl...tat-b8-audi-s4

[thebatmanfan]

Yes I ended up calling the local dealership and they said it was an N10412804. They ordered one for me and I'll be picking it up on Tuesday.

[Nelson G]

Before starting the job, I created a sheet with labels corresponding to the part which screw and socket I needed, and the torque spec. I put the labels in plastic bags so as I took the item apart I placed the screws in the individual bags. It helped me so I did not have to figure out which screw went where.

[thebatmanfan]

Yeah I'm keeping track similarly. I don't think that was my problem here. I was missing one during disassembly. It wasn't on the car. Now that I'm putting everything back, I'm remembering that this one was the one I was missing. Got it ordered and picking it up this afternoon.

[thebatmanfan]

Finally got that screw in. I installed it and pressure tested. Still doesn't hold pressure. I figured I could fill it up with distilled water and try to pressurize and locate the leak. The leak is still at the connection where the crossover pipe enters the thermostat! I guess I'll be taking out the crossover pipe to inspect it for cracks or holes, and the gasket for a good seat. Will update when that's done.

[thebatmanfan]

Crossover pipe and lower radiator hose (drain valve leak...smh) are both replaced and the system holds vacuum. I filled the system and am in the process of hooking up sensors and vacuum lines, but I am stuck at one. Probably should have taken pics, but it's not like I can get back there in some places with a camera. Take a look at the diagram here

This is the view of the solenoid tree at the back of the supercharger, looking from the firewall toward the front of the car. Can someone tell me where the hose listed as number 1 in the pic comes from? I see a loose hose off the hvac heater control valve that would fit, but I am concerned because it's much more flexible than the other vacuum hoses, and it could be a vent or drain for the control valve. Could this be hose 1?

[SwankPeRFection]

There’s only one hose back there that hangs loose when you take it off and it’s not formed like the ones going to the 3 top solenoids. Also, don’t force the others to make them fit. They all line up easily and if you’re having to force them to fit, it’s wrong.

[thebatmanfan]

Yes there is one back there that comes from back under the cowl. It's a small much more flexible line that comes off of the HVAC heater control valve. Is this the one you are referring to? It's the thinnest hose in this assembly:

[thebatmanfan]

I got it all back together, running, and then decided to bleed from the supercharger bleeder screws. I got both sides bled, tightened the driver's side fine, but when I tightened the passenger's side, the hole bleed port broke off the SC intercooler. I wasn't applying a whole lot of pressure. Is there a way to fix it without buying a new SC intercooler? Maybe some marine JB weld? I'm really at a loss here. It was literally back together and running and something breaks...photos here...
https://imgur.com/a/JUlXlcz

[SwankPeRFection]

What’s up with the vice grip marks on that bleeder neck? I’m almost wondering if there wasn’t already some damage to it from twisting and this led to the failure. Also, those metal screws aren’t a good idea due to this. You can easily apply too much torque if you’re not using a driver that’s just a screw driver handle and it’s a wrench instead. It’s too much torque and sometimes because one of aluminum and the other stainless steel, there will also be a metal oxidation bond that develops between them and locks up the screw where this could happen. In all honesty, the plastic ones are fine if you use a proper large size Phillips screwdriver. I wouldn’t JB weld it, but that’s your call. How old are those cores? If they’re original or have never been changed in a lot of miles, maybe it’s time just from a peace of mind standpoint to reset the clock on them. They almost always pop.

[thebatmanfan]

The vice grip marks were from me getting the screw back out of the neck. I am going to try the JB weld. No loss if it doesn't hold. If it doesn't work, new core it is. Thanks for the advice!

[thebatmanfan]

Okay everything is back together on the motor. Last thing of concern is a constant hissing (sucking air) in the area shown in the pictures here...

I have been thinking it might be this guy, but the vacuum hose connection is not the leak point...

Are these a failure part? It looks like it might have a diaphragm in it? Do those burst and cause hissing?

It hisses during idle, and sometimes goes away when revving, but quits doing that after a few times. It hisses all the way through shut off and hisses for a second or two after, like it's leaking down. I cannot feel air passing through anywhere when feeling around with my fingers.

[SwankPeRFection]

You sure you didn’t crack that front black hose that clips in there when you moved it around? It also had another part on the left that clicks into it, another fitting… sometimes that doesn’t go together easily and doesn’t seat properly. Also, if you didn’t put all the orings back on properly or were fighting with the supercharger when you put it back on, one could have slipped or maybe you’re just missing it. If you scan it, you should have a code for vacuum leak somewhere. If you had messed with the IC cores in the supercharged I’d have said it could be around the front oring there that it’s leaking since those are easy to roll/pinch when seating the cores all the way if they’re not lubricated or if they’re just not perfectly aligned, but you’d be able to feel it with your fingertips.