Coolant leak after installing new crossover coolant pipe.

[WimpyS4]

I had a small leak develop and thought it was the thermostat or crossover pipe because it was coming from there. Thermostat was fine and functional but still replaced, water pump was not leaking but still replaced. Crossover coolant pipe connection to the thermostat was deteriorated and had coolant pooling so I guessed that was where the leak was coming from. DIY replaced pipe and all o-rings. There was still coolant pooled up and streaks over the front of the engine and I cleaned up what I could, but there was still coolant dripping from the passenger side of the oil pan with the engine on. The longer I had the engine turned on the faster the stream. I bled the whole system and it took about 1.5 gals to max then took it out for a test drive and steam kept coming from the passenger side. Temps stayed at 199-213C. When I got home and checked coolant level, it was 3 inches below min and there was some coolant on the passenger side of the metal skid plate. I can't find where it could be coming from. I checked all the bolts are torqued to spec and its does not look like its coming from the crossover pipe, water pump, or thermostat. Supercharger IC cores are also intact. Radiator and intercooler are dry; it seems to be coming from the passenger front of the engine. Any ideas?

EDIT: Vacuum tested system before filling coolant. Held with a small gradual loss for 10 mins at 1 bar. Supercharger valley was dry so I'm guessing its not the PCV.

[TappaNuKegga]

How did you verify that your supercharger valley was dry?

[Ford Prefect]

I had an annoying slow coolant leak. Might not be the exact same as your but there was never any on the ground. It turned out to be the temp sensor on the crossover pipe. I can’t believe I couldn’t find it.


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[430hps4]

I would just confirm that all the gaskets are lined up correctly. Usually, on that cross-over pipe, the most common leak comes from where it goes into the thermostat. The pipe likes to crack right there.

Since you are working on a new pipe, and its leaking from the passenger side, I'd guess maybe the gasket/o-ring is messed up somehow. Or the other coolant pipe o-ring on that side isn't quite tight...

[WimpyS4]

How did you verify that your supercharger valley was dry?

I had the supercharger off and did a thorough inspection. Also highly doubt it's the pcv because it's coming from the front passenger side.

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[WimpyS4]

I would just confirm that all the gaskets are lined up correctly. Usually, on that cross-over pipe, the most common leak comes from where it goes into the thermostat. The pipe likes to crack right there.

Since you are working on a new pipe, and its leaking from the passenger side, I'd guess maybe the gasket/o-ring is messed up somehow. Or the other coolant pipe o-ring on that side isn't quite tight...

That's what I initially thought but felt around the connection to the thermostat and both head connections and it was bone dry. I can't visually see where it could be coming from. Every oring was lubed before installation. I just wonder if there is a oring on the passenger side connection to the crossover that I missed. Another thought I had was the hard plastic pipe under the sc that connects the other side of the thermostat but I haven't found anybody that shows the symptoms a leak from there.

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[Mfryman1]

Go old school, drain as much out as possible and pressurize 10-12 lbs. and spray with soapy water.

[WimpyS4]

Found the leak. Tstat o ring was pinched during install . Luckily pulling the supercharger the second time is much easier.

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[BlackJon]

Found the leak. Tstat o ring was pinched during install . Luckily pulling the supercharger the second time is much easier.

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Sorry to bother you but I think I'm have the same issue.. just did the coolant crossover and I see I bit of coolant coming out.. how did you go about fixing the gasket.. just took off the supercharger and ..... then ..
I don't want to put the car in service mood or take anything apart if I don't have to.

Thanks so much 20211109_210432.jpg20211109_210453.jpg20211109_210648.jpg

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[WimpyS4]

Sorry to bother you but I think I'm have the same issue.. just did the coolant crossover and I see I bit of coolant coming out.. how did you go about fixing the gasket.. just took off the supercharger and ..... then ..
I don't want to put the car in service mood or take anything apart if I don't have to.

Thanks so much 20211109_210432.jpg20211109_210453.jpg20211109_210648.jpg

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what you're having is probably the oring that connects the pipe to the tstat is leaking. Get a pressure tester and see if it is that. You don't have to put the car back into service to fix it it's just good to have someone else to help hold shit. The oring that Audi preinstalls onto this pipe is not good and that is most likely where your leak is coming from. Rent a pressure tester from autozone and see if you can hear the leak. And feel all around where the pipe connect to see if u can feel air moving. If it is then it's the oring.

To fix pull out the two screws on the left side of the pipe, take off the water pulley, then back out the screws on the right side but not all the way. Should give u enough room to pull the pipe off, get a pick under the oring and pick it off and install a new one but it's gonna be tight.


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[BlackJon]

Dealing with the O ring I don't need to take off the supercharger

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[BlackJon]

what you're having is probably the oring that connects the pipe to the tstat is leaking. Get a pressure tester and see if it is that. You don't have to put the car back into service to fix it it's just good to have someone else to help hold shit. The oring that Audi preinstalls onto this pipe is not good and that is most likely where your leak is coming from. Rent a pressure tester from autozone and see if you can hear the leak. And feel all around where the pipe connect to see if u can feel air moving. If it is then it's the oring.

To fix pull out the two screws on the left side of the pipe, take off the water pulley, then back out the screws on the right side but not all the way. Should give u enough room to pull the pipe off, get a pick under the oring and pick it off and install a new one but it's gonna be tight.


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Dealing with the O ring I don't need to take off the supercharger?

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[BrokeBichB8]

Dealing with the O ring I don't need to take off the supercharger?

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I bought 2 pressure test plugs on amazon and pulled the supercharger and plugged coolant lines so I could confirm leak with pressure tester was at thermostat crossover interface. Shitty thermostat was too large Id, new coolant O-ring didnt fix problem. I think its in your best interest to pull supercharger to source the leak though

[WimpyS4]

Dealing with the O ring I don't need to take off the supercharger?

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Correct. It'll be tight but it's doable. Just to be sure ur talking about the oring on the crossover pipe not the thermostat.

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[WimpyS4]

I bought 2 pressure test plugs on amazon and pulled the supercharger and plugged coolant lines so I could confirm leak with pressure tester was at thermostat crossover interface. Shitty thermostat was too large Id, new coolant O-ring didnt fix problem. I think its in your best interest to pull supercharger to source the leak though

The new coolant crossover pipe from Audi is a superceded part and the oring they provide does not create a seal. You have to use the oring that's usually included in the thermostat replacement kit from fcp or ecstuning.

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[BlackJon]

Correct. It'll be tight but it's doable. Just to be sure ur talking about the oring on the crossover pipe not the thermostat.

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Did you get a different gasket.. or is it called and O ring. Can I get one from a store or do I need to order one if neededScreenshot_20211110-214709_DuckDuckGo.jpg

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[WimpyS4]

Did you get a different gasket.. or is it called and O ring. Can I get one from a store or do I need to order one if neededScreenshot_20211110-214709_DuckDuckGo.jpg

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It's this guy. https://www.ecstuning.com/b-victor-r...6e121119h~vic/
Might be able to get it from your local Audi.

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[alphaphaedrus]

I know this is an awfully old thread but I wanted to resurrect to see how folks are dealing with this. I bought a replacement crossover pipe that seems to have some dimensions slightly wrong. The upper rad hose connection is too tight for replacement hoses (lubed, forced, etc. - only the old crusty connector would fit on), the lower quick connect seems a little small so leaked until I put on a larger oring, and the crossover/tstat connection leaks. I was planning on trying a larger o ring on the latter to see if that stopped the tstat leak but am wondering if I should just get a better brand crossover, OEM/Vaico/Reinz vs whatever no name the one I bought off partsgeek is. Please share any experiences you have fixing this for good.

[raceshop147]

I just replaced PN VAI-V105324 / 06E121045BD

Bought from FCP euro with a lifetime replacement guarantee


While servicing the supercharger I also replaced other items





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[STXA7]

I know this is an awfully old thread but I wanted to resurrect to see how folks are dealing with this. I bought a replacement crossover pipe that seems to have some dimensions slightly wrong. The upper rad hose connection is too tight for replacement hoses (lubed, forced, etc. - only the old crusty connector would fit on), the lower quick connect seems a little small so leaked until I put on a larger oring, and the crossover/tstat connection leaks. I was planning on trying a larger o ring on the latter to see if that stopped the tstat leak but am wondering if I should just get a better brand crossover, OEM/Vaico/Reinz vs whatever no name the one I bought off partsgeek is. Please share any experiences you have fixing this for good.

Better brand is velocityAP ports with universal 3/4” hose IMHO


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[PenttisHSR]

I know this is an awfully old thread but I wanted to resurrect to see how folks are dealing with this. I bought a replacement crossover pipe that seems to have some dimensions slightly wrong. The upper rad hose connection is too tight for replacement hoses (lubed, forced, etc. - only the old crusty connector would fit on), the lower quick connect seems a little small so leaked until I put on a larger oring, and the crossover/tstat connection leaks. I was planning on trying a larger o ring on the latter to see if that stopped the tstat leak but am wondering if I should just get a better brand crossover, OEM/Vaico/Reinz vs whatever no name the one I bought off partsgeek is. Please share any experiences you have fixing this for good.

You need to get OE from Audi, the non-genuine pipes are a slightly different size.

[alphaphaedrus]

Thanks