Need help identifying coolant leak (Pictures inside)

[TylerT]

Hello everyone,

Just hoping I can get some guidance here, If I posted in the wrong subforum I do apologize in advance.

My 6MT S4 is just about at 119,000mi and after leaving work last Friday, I noticed a large pool of coolant under the car. When I put the cooling system under ~15psi via the expansion tank, It's tricking down heavily on the driverside of the transmission area. Not a drop of coolant on the passenger side.

I verified the expansion tank does have a slight crack (replacement on the way, very slow leak) , although the majority of the fresh fluid seems to be pooling around this area in the pictures below, pretty much where the engine & transmission connect. The hole you see is circled in this picture:





Driverside:




Any ideas?

[hibiscusS4]

Id check the coolant rail in the back. It could be leaking from the head


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[Corradovolksb]

It might be the drivers side heater core hose connection to the hard pipe

[themadscientist]

Check the crossover pipe as mentioned above, and check the block valley to see if coolant is pooling up there. There's a ton of seals that can leak back there. Best to pull the intake and refresh everything at once.

[Zba]

It's probably your auxiliary coolant pump. When the pump goes it will fill the valley and leak out whichever way is easiest.
As stated above; check under your intake.

[insomniacxp1]

Check under intake but most likely coolant crossover or temp sensor

[TylerT]

Thank you for all the helpful responses,

I looked under the intake manifold with a flashlight and I did see some signs of dried up coolant, I'd say the auxiliary pump is a good place to look first.

I'm picking up some intake manifold gaskets today from a local shop and last but not least, a Bentley service manual

[christianb5s4]

I can tell you that, coming from someone aka me that had coolant leak from both the auxiliary pump as well as the heater hose connector on the back of the engine, that looks much more like the heater core hose coupler leaking.

[TylerT]

Curious, was the leak obvious and in plain visible sight? What part # on this diagram are you referring to?



Thanks much!

[Kaane]

Rear main seal flange could be leaking as well, that paper gasket always fails.

[QuinnsterKID]

Just a tip..... if you pull the coolant hard line running on the back of the cylinder heads, make sure you replace every O ring that attaches to it. Especially the one the goes on the pipe that runs to the front of the block. That will also fill your valley. Once an O ring has been pulled they do not seem to reseal the same as if they were new. Trust me.

[TylerT]

You guys were right, Auxiliary water pump appears to have leaks everywhere. After pulling the manifold, I put the expansion tank under pressure and there's a steady stream of fresh coolant in this area.

Also, appears to have been happening for some time considering the insane amount of dried coolant that has pooled.



I also managed to break both lines that connect to the rear if the manifold (PCV spider hose and something else?) ... damn brittle plastics

Either way, learning experience! I'm excited to get 'er back on the road. ,

[vavJETTAw36]

Relocate that sucker to the back of the engine.


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[jballou]

Relocate that sucker to the back of the engine.


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Why?

[vavJETTAw36]

Why?

More horsepower!

Just messing around. Easy access for when it leaks again. Yes, it will leak again. When? Who knows. But you'll be able to swap it under 10 min


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[Zba]

For the once every 10-15 years you would need to change the pump, is it really worth the effort to relocate? No.

[JVD]

Agreed.

Aux pump is one of the simpler tasks on these cars.

[TylerT]

Replacement parts are on the way, installation looks to be a breeze.

Maybe somebody could point me in the right direction .. what are the 2 intake manifold connections on the back?

One of them connects to the PCV spider hose, not sure about the other one.



Thanks a million guys.

[jballou]

For the once every 10-15 years you would need to change the pump, is it really worth the effort to relocate? No.

Exactly.

[wbrunner23]

Spider hose and brake booster

[TylerT]

Leak fixed, tested 15 psi for 15 minutes and there wasn't a drop in the bucket.

Time to jerry rig some vacuum hoses and order a few replacement pieces.

Thank you everybody for the help!