3.0 rear water crossover pipe

[86turbodsl]

Ok, i think my rear crossover pipe is leaking. There was two types of these made. A steel one used on early B6, and the later plastic one used on end of production B6. There's also the B5 2.7 / 2.8 one. Which one should i purchase? Mine is currently plastic, but is the plastic one the fragile one? Any advice for me?

[imnuts]

To guarantee that it will fit and work properly, get the same thing. Are you sure that it is the pipe itself that is leaking though and not a connection point with a bad o-ring? I'd verify the leak location before buying anything.

[86turbodsl]

No, i'm not 100% sure, other than finding others that have had the same issues, as you know, it's exceptionally hard to view this area.
It's my daily so pulling the manifold for a look see is not my preferred way to go. I have to get something done before winter though,
i've been filling with water for now.

[diagnosticator]

No, i'm not 100% sure, other than finding others that have had the same issues, as you know, it's exceptionally hard to view this area.
It's my daily so pulling the manifold for a look see is not my preferred way to go. I have to get something done before winter though,
i've been filling with water for now.

If for some reason you can't or don't want to deal with this leak now, use only 50%/50% Distilled water/G12 Antifreeze mixed coolant to refill the cooling system. If only water is used, the cooling system will become only water after awhile, and will be damaged from corrosion and likely eventual coolant pump failure from loss of lubrication for the coolant pump shaft seal. With only water, the cooling system is also more likely to overheat and loose coolant due to over pressure resulting in a run-away loss of engine cooling that can also damage the engine.

[86turbodsl]

I know about this. I'm doing a timing belt this fall. If the water pump goes, it's getting replaced anyway.
There isn't enough time to have major corrosion either. G12 is too expensive to keep throwing it away.
Only local source is dealer at $40/gallon.

[diagnosticator]

I know about this. I'm doing a timing belt this fall. If the water pump goes, it's getting replaced anyway.
There isn't enough time to have major corrosion either. G12 is too expensive to keep throwing it away.
Only local source is dealer at $40/gallon.

When the concentration of anti corrosion additives in the coolant drops below the minimum required, corrosion begins immediately, and will progress rapidly. Also, since G12/ethylene glycol inhibits surface boiling in the hottest locations in the cylinder head and block cooling jackets, will allow surface boiling to occur uncontrolled that will erode the jacket surfaces quickly due to steam bubble implosion erosion of the jacket surfaces. Chemically raw aluminum will be corroded at a high rate without anti corrosion chemicals in the coolant to protect the exposed jacket surface material. Aluminum without a protective surface layer of aluminum oxide, has practically no resistance to rapid corrosion and chemical dissolving processes that will occur. You risk an expensive engine for the sake of the comparatively low expense of lost G12. Continue your misguided scheme if you insist, it's your car, and your money at risk if you do. Consider purchasing a supply of Pentosin G12 online. The 3.0l block and heads are aluminum, not cast iron. Avoid the likely damage by fixing the leak now instead of later.

[86turbodsl]

Thank you for your concern. I deal with metallurgy often as an engineer. I'm aware what corrosion is and how to avoid it. I was posing this question to get experience from those who have dealt with this coolant pipe in past. I have plenty of experience with engines, but not a lot with Audi 3.0L.

[SJorge3442]

Thank you for your concern. I deal with metallurgy often as an engineer. I'm aware what corrosion is and how to avoid it. I was posing this question to get experience from those who have dealt with this coolant pipe in past. I have plenty of experience with engines, but not a lot with Audi 3.0L.

This pipe isnt fun to swap. Get a new one and get it on asap. Leaking cooling systems dont cool the engine as thoroughly since they arent under the proper pressure. Using water is silly and bound to get you in trouble down the road later. Order up some G12 from ECS if you want and mix your own 50/50 with DISTILLED water until you can get this fixed. Remember, its gonna suck when the leak really blasts through and your stranded in the worse place possible.

[86turbodsl]

Point taken. I'll get a plastic one coming as soon as i can. Any tips on changing it? Or just like it looks, remove intake, and as much of the rear hardware as required to get to the flange fasteners?

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[SJorge3442]

Point taken. I'll get a plastic one coming as soon as i can. Any tips on changing it? Or just like it looks, remove intake, and as much of the rear hardware as required to get to the flange fasteners?

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I believe its as simple as removing the intake (watch out for the plastic dowels that ALWAYS break when you remove the intake) and then getting at all the fasteners and clamps. TBH, I would suggest doing 2 other jobs while doing all of this.

#1 Vacuum Lines. Replace them all with silicone tubing. Theres a DIY on here by SlickFix which is the best guide to use.
#2 Replace ALL PCV lines with 3/4" heater hose. If your lines are original, they WILL break when you touch them. Using a combination of heater hose and brass elbows, you can easily make a new PCV system for <$30 compared to over $150 for more brittle plastic lines.

Other than that, you should be good to go for a while after changing all of this out.

[kNightsfallen]

You have to get a good eye on where the leak is coming from. The cross pipe goes from head to head with an o ring to seal each side. But there is a nipple towards the drivers side. Most of the time it's just the nipple that leaks. If you have the metal pipe the nipple unscrews and can be replaced. If it's plastic the whole pipe needs to be replaced.
I'll be honest the pipe replacement sucks. Like call in sick the next day and hope they give it to someone else sucks... Lol


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[imnuts]

Can you pick up our rent a pressure test kit to find the leak with the engine cold?

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[19jdog]

When I did my head gaskets. My original o ring on the metal coolant pipe broke when I pulled it apart. I didn't know this until I put everything back together and started her up. I had to tear the whole front of the motor apart just to fix a 2 dollar o ring from napa auto parts. I was so fucking pist. Anyway you will need to get in there and take shit apart to find out where that leak is. Don't mess around with just water in the radiator like others have said. Don't cut corners not worth it..


BTW
04 with metal coolant pipes

[pablolizarraga]

I just ended up purchasing pipe from dealer once I confirmed leak was coming from the pipe (whether $1 o-ring or $100+ pipe) because chances are that... well you know. Cheapest one I found was from https://www.europaparts.com/radiator...e0121101j.html
The pipe's branch at top arrow was disintegrated. The end of the other pipe was starting to corrode.

I believe its as simple as removing the intake (watch out for the plastic dowels that ALWAYS break when you remove the intake) and then getting at all the fasteners and clamps. TBH, I would suggest doing 2 other jobs while doing all of this.

#1 Vacuum Lines. Replace them all with silicone tubing. Theres a DIY on here by SlickFix which is the best guide to use.
#2 Replace ALL PCV lines with 3/4" heater hose. If your lines are original, they WILL break when you touch them. Using a combination of heater hose and brass elbows, you can easily make a new PCV system for <$30 compared to over $150 for more brittle plastic lines.

Other than that, you should be good to go for a while after changing all of this out.

Great tips! I also ended doing the JHM spacers ($100) https://jhmotorsports.com/shop/catal..._62_64_234_301

Good luck!


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[pablolizarraga]

Oops. Wrong link. That's the new leak I'm dealing with. I erased from my mind the $140 I paid to Audi for the pipe.


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[pablolizarraga]

And... these manuals were invaluable as a guide.

Manifold removal
http://workshop-manuals.com/audi/a4_...nd_installing/


Coolant pipe removal
http://workshop-manuals.com/audi/a4_...t_pipe_(rear)/


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[diagnosticator]

Thank you for your concern. I deal with metallurgy often as an engineer. I'm aware what corrosion is and how to avoid it. I was posing this question to get experience from those who have dealt with this coolant pipe in past. I have plenty of experience with engines, but not a lot with Audi 3.0L.

Then proceed as you want, it really does not matter to me one way or the other. However, the choice of running straight water in the cooling system, seems inconsistent with your engineering background. And it must be stated so that others reading this don't assume water only is an acceptable option. I understand why you posted your request, however when someone mentions something of a technical nature, and the information is not correct, it is assumed the poster is misunderstanding something or is just uninformed, and it seems like a good idea to point that out.

I don't know and cannot know what you or anyone else posting here knows or does not know about the technical field and details involved.

[86turbodsl]

Finally getting to tackle this, found a metal crossover instead of a plastic as ecs insisted my 04 would have. The g62 sensor was so loose it would freely rotate. Oring was almost completely disintegrated. Whats the likelyhood that there is more damage to the crossover? I dont really want to yank the manifold if i dont have to, and i would need to swap the plastic crossover i bought for a metal one. I have a new g62 here ready to go in. Pressure test is not easy as the whole front is off for the timing belt i just finished.

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[19jdog]

Finally getting to tackle this, found a metal crossover instead of a plastic as ecs insisted my 04 would have. The g62 sensor was so loose it would freely rotate. Oring was almost completely disintegrated. Whats the likelyhood that there is more damage to the crossover? I dont really want to yank the manifold if i dont have to, and i would need to swap the plastic crossover i bought for a metal one. I have a new g62 here ready to go in. Pressure test is not easy as the whole front is off for the timing belt i just finished.

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That's was my problem, my o ring was toast. I went to the near by Napa Auto Parts and replaced the damaged one. Been good ever since.

[86turbodsl]

Ended up yanking the manifold. Valley is oily. The pipes are all metal, and generally look good. Should i go after all the orings while i have it apart? Car is 185k, even the pcv hoses are solid. No crumbly.

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[SJorge3442]

Ended up yanking the manifold. Valley is oily. The pipes are all metal, and generally look good. Should i go after all the orings while i have it apart? Car is 185k, even the pcv hoses are solid. No crumbly.

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Hmm. If that valley is oily its gotta be because the PCV lines are blowing oil out (pressurizing) or the valley pan gasket is leaking. I'm usually not one for "while you're in there" repairs but in this case I would recommend fixing the leak thats causing that oil to gather. What o-rings are you refering too? The ones on the cross over pipe? If your replacing the pipe YOU NEED to change those rings. Otherwise I'd bet the pipe would start leaking when it first gets under pressure. I'm flabbergasted that the PCV lines are in ok shape. They must have been changed at some point. Even so, I would probably just swap out the lines for some custom heater hose lines just to be on the safe side for future issues.

[86turbodsl]

Ill post a pic later. Could the pcv lines condition be related to my duty cycle? I commute 60 miles all highway, almost never in stop/go traffic. That plastic has gotta be heat sensitive and degrade at temp. The o rings on the metal crossover pipe. I got a new G62 sensor because the fans run on high at startup, i figured the sensor was bad. The coolant pipe looks good, still has paint on it, and no real evidence of leakage that i can see, but if one o ring disintegrated, maybe the others are on the way out? I was probably going to send the plastic pipe back to ECS. If the metal line is not corroded, i see no reason to replace it. My only other repair is to fix the broken IMRC actuator coupling. That's another story.

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[SJorge3442]

Ill post a pic later. Could the pcv lines condition be related to my duty cycle? I commute 60 miles all highway, almost never in stop/go traffic. That plastic has gotta be heat sensitive and degrade at temp. The o rings on the metal crossover pipe. I got a new G62 sensor because the fans run on high at startup, i figured the sensor was bad. The coolant pipe looks good, still has paint on it, and no real evidence of leakage that i can see, but if one o ring disintegrated, maybe the others are on the way out? I was probably going to send the plastic pipe back to ECS. If the metal line is not corroded, i see no reason to replace it. My only other repair is to fix the broken IMRC actuator coupling. That's another story.

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Ah gotcha. So you're leak is from an o Ring on the cross over pipe, not the usual spot (throttle body heater nipples)? Either way, i recommend replacing any o ring on that pipe whether you use the old or new pipe. 185k miles is a lot for a ring to be on an engine and then reused.

In regards to the duty cycle comment, what do you mean? Have you been having issues with the emissions cycle properly completing? I cant foresee that being a PCV issue if your getting a cat related code.

[86turbodsl]

All im saying is i think my drive cycle is pretty easy. Slow warm up then hwy then cooldown then park. Lots of airflow. I think your probably right to change orings. Not looking forward to yanking the pipe. The only obvious leak was from the green sensor.

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[SJorge3442]

All im saying is i think my drive cycle is pretty easy. Slow warm up then hwy then cooldown then park. Lots of airflow. I think your probably right to change orings. Not looking forward to yanking the pipe. The only obvious leak was from the green sensor.

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Ohhh. I thought it was leaking at multiple spots. My bad for not reading all the way through. If you're only leak is at the sensor, just change that. Don't pull that pipe if you dont have to!

[86turbodsl]

Ok. Ive got a mirror i can look around for more trails. Im not sure i should mess with the pcv if its gone this far and still solid. Ill get a photo of the valley later.

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[86turbodsl]

Heres the valley and a shot of the ect area.



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[86turbodsl]

Thought i'd update this for anyone looking later:

The coolant pipe on my engine turned out to be steel, differing from the prevailing wisdom of a late 04 build. the problem was the o-rings had deteriorated and i just had to put new coolant sensors in. I returned the plastic coolant crossover i bought.

[clarkthashark]

Thanks for the Update. I've just started a small coolant leak that seems to be coming from the metal coolant cross pipe. It may just be an o-ring but I'm not looking forward to fixing it.

[vtince]

Anyone have any tips on how to remove the coolant hose that goes towards the firewall from the crossover pipe?

Also, I have the the two top and bottom bolts on the passenger side of the crossover pipe removed, but on the drivers side of the pipe, I have only gotten the top bolt, any idea on how to get the bottom bolt out, kind of a tough angle... thanks in advance.

[2004a4b630QT]

^Did you try a wobble socket and/or extension? or a u-joint.

My coolant pipe on my 04 is metal too.

I had a leak issue because I inserted the sensor with the o-ring on it and it never seated right. Twice. The trick was to put the o-ring into its groove first, and then pop in the sensor. No leaks since.

[pablolizarraga]

Anyone have any tips on how to remove the coolant hose that goes towards the firewall from the crossover pipe?

Also, I have the the two top and bottom bolts on the passenger side of the crossover pipe removed, but on the drivers side of the pipe, I have only gotten the top bolt, any idea on how to get the bottom bolt out, kind of a tough angle... thanks in advance.

If youre referring to the heater hose coming from firewall to driver side of engine, I removed MAF hose and CPRV. Pry hose clip w/ a screw driver and start wrestling w/ it. It will come off little by little.

But if youre dealing w/ crossover pipe, I would hope you have intake manifold off. In which case, a Husky Microdriver will come in handy for that bolt and many others.

IMG_5321.JPG

[vtince]

If youre referring to the heater hose coming from firewall to driver side of engine, I removed MAF hose and CPRV. Pry hose clip w/ a screw driver and start wrestling w/ it. It will come off little by little.

But if youre dealing w/ crossover pipe, I would hope you have intake manifold off. In which case, a Husky Microdriver will come in handy for that bolt and many others.

IMG_5321.JPG

Yea that heater hose is what I’m talking about. This is what it’s looking like right now. Still seems like a pain to get to the clip/hose IMG_1997.JPG

As for that bolt, I’ll give it a try.


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[pablolizarraga]

Yea that heater hose is what I’m talking about. This is what it’s looking like right now. Still seems like a pain to get to the clip/hose IMG_1997.JPG

As for that bolt, I’ll give it a try.


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Try to move aside as many wires/hoses. I cut some retaining clips to move harness and combi valve hoses. Allen keys will also help out for that bolt.


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[vtince]

Update:

-For the heater hose, I cut the zip ties from wiring harness near the hose and move everything away as possible. Then used a pick tool to pull on the metal retaining clip and a flathead screwdriver as leverage to push the hose off the rear coolant pipe.

-For the driver side lower bolt on the rear coolant pipe, with the wires moved to make room, I got a wrench with an small extension and got it behind the pipe. Room was limited so basically I was going 1-2 clicks on the wrench at a time.

So the leak... its coming from the oring on the front of the rear coolant pipe. When I pulled it off, it was basically gummy and distorted. Got all the other o-rings to be replaced now.


As a reference to others when doing this job, here are the o-ring part number you need (Since you have it off, replace all o-rings):

For PLASTIC rear coolant pipe (06C121085H):
2x 06E121119A (Rear Coolant Pipe to Cylinder Heads)
1x 06C121119A (Rear Coolant Pipe to Front of Block)
1x N90519701 (Rear coolant pipe to metal return pipe)
1x N90380002 (Metal Feed Line that is on top of the rear coolant pipe to Block, needs to be removed to get to the Rear Coolant Pipe)
1x N90316802 (Temperature Sensor to Rear Coolant Pipe)
1x 3B0122291B (This is a connector, you only need the o-ring that is included since Audi doesn't sell only the o-ring. This is for the Heater Hose to Rear Coolant Pipe)


For METAL rear coolant pipe (06C121085F):
2x N90912501 (Rear Coolant Pipe to Cylinder heads)
1x N90925001 (Rear Coolant Pipe to Front of Block)
1x N90765301 (Rear Coolant Pipe to Metal Return Pipe)
1x N90380002 (Metal Feed Line that is on top of the rear coolant pipe to Block, needs to be removed to get to the Rear Coolant Pipe)
1x N90316802 (Temperature Sensor to Rear Coolant Pipe)
1x 3B0122291B (This is a connector, you only need the o-ring that is included since Audi doesn't sell only the o-ring. This is for the Heater Hose to Rear Coolant Pipe)

[Turbo510]

Against all good common sense, I did not replace any O-rings on my '05 with plastic coolant pipe, and have absolutely no leaks. The rings all were in excellent, pliant condition when I removed them, but I did smear a film of Permatex Silicone sealant on the O-rings and also in their receptacles. Incidentally, that heater hose connection to the coolant pipe was kind of difficult, due to there being almost no working room.