Q7 TDI - Beware that EGR Cooler!

[Avantly]

Wanted to post this here in case anyone with the TDI end up with a sudden coolant consumption issue with no external leaks (i.e. not the normal "my oil cooler filled the valley with coolant and oil".

2014 CNRB Q7, suddenly started using coolant a few weeks ago, went from very minor to very severe, very quickly. I figured it was leaking, pressure test, no leak but pressure bled down fast. Crap. At this point I knew it had to be internal and either EGR cooler or head gaskets, and I know head gasket failure is relatively rare on these things.

I tried to attach a pic but the picture attachment doesn't seem to be working right now, or I am mentally challenged. My belief from my forum research is that head gasket failure on the 3.0TDI's is uncommon so I immediately went for the EGR cooler. The intake side of the cooler was completely full of coolant from the pressure test and it was filling into the intake, when I pulled the bolts off the ASV coolant started pouring out. If I would have tried to start the engine after the pressure test I would have hydrolocked and grenaded this poor engine.

Oil looks maybe slightly gray on top of oil cap, doesn't appear to be much in the oil, but this problem didn't go on for very long so I wouldn't expect the oil to be milkshake at this point.

Just beware if you end up with a mystery coolant leak on these things, IMMEDIATELY inspect that EGR cooler! Eliminating them is quite easy, and the best part is that afterward, you can actually reach under the intake afterward to insert the inner intake manifold bolts...

[Audibot]

Another thing to put on the checklist when I go through my engine.

I did my water pump back in September (vacuum filled), which meant it was a slight shock when the coolant dropped after it got cold. Guess it needed to refill the heater core. So far so good on that front since.

[NorthernGTI]

Just beware if you end up with a mystery coolant leak on these things, IMMEDIATELY inspect that EGR cooler! Eliminating them is quite easy, and the best part is that afterward, you can actually reach under the intake afterward to insert the inner intake manifold bolts...

How would one go about doing this? To be honest, I don't even know where it is.

[Avantly]

How would one go about doing this? To be honest, I don't even know where it is.

I thought I replied to this but I guess I never clicked the post button!

I suspect the #1 symptom (with no testing) for this failure will be coolant leakage with no external leak (including the common leak into the valley).

Testing would be normal cooling system pressure testing (I use a relatively cheap Taiwan made kit and it is great but I had to buy the Audi coolant tank adapter separately) and any pressure loss (with no external leak) should be highly suspect for the EGR cooler.

Visual inspection would require removing that last piece of hard intake tube between the ASV and the intercooler hose - It is held on by 4 long bolts that go through the ASV to the inlet of the manifold, one bracket bolt you can see on the bottom of the tube just to the passenger side of the pipe inlet, and one bracket bolt near the first one but opposite side of EGR tube, and this second bolt is facing down, it sits just behind the drivers side of where the EGR tube goes into the intake hard pipe.

Once you remove these bolts and the metal clamp ring that holds the EGR tube to the hard pipe, you can remove the hard pipe section and look directly into the EGR tube. The seals are usually reusable if in good shape and not terribly old.

I can not get any pictures to upload on AZ, here is a link to an external one - This picture is looking down into the EGR tube after removing the intake hardpipe, after I vacuumed coolant with my shop vac until it appeared empty (and then it filled back up this far just from gravity/whatever was still left inside the cooler) - The black pipe you see on the right is the hard pipe I removed, it was just set off to the side with rags stuffed in it so it would dry out while I was vacuuming the EGR tube lol:

[NorthernGTI]

Ill have to double check. I haven't had any major coolant loss lately. I did top off the coolant slightly(maybe a couple mm) but we've had some pretty cold weather in Toronto area last couple days(-17C..0*F) so Im assuming its due to that(hopefully).

[Avantly]

This was more than a minor coolant loss... I filled it after completing the oil cooler job about a year and a half ago, topped it off after a week of driving, and all was well until suddenly the low coolant light came on; I refilled it, and noted that the thing needed to be checked for leaks (I figured the original water pump was on the way out). A few weeks after that it suddenly used a half gallon and it got parked immediately when I didn't see any sign of external leaks anywhere. So glad that it didn't turn catastrophic, I have so much work into this car it would be rather disappointing to have one of the connecting rods suddenly leave the chat! It crossed 150k miles last year and I've been through nearly every major issue that occurs on these things and hoping it will go to 300k. I still have to pull the engine to address the sump oil leak issue but parts for that job are minimal... Hopefully thatis the last big job that this car needs until it starts approaching 300k miles xD

[AudiNike12]

Another coolant leak that's maybe not as common or maybe it is. It's the plastic cover/flange that's bolted on the backside of the big front engine cover. It connects to the oil cooler with a small rubber hose. It happened to me a couple of months ago. All of a sudden on my way home from work, the coolant warning sounded off and told me to shut off the engine. Had to tow the car home. There were tons of coolant in the valley and my first thought was the oil cooler. I stripped it down and replaced all the gaskets on my way there. Pressure tested it and it still filled up the valley with coolant. Had to strip it down again. This time I filled up the coolant with everything out of the way and I saw a stream of coolant coming from the bottom of this plastic cover. A PITA job to replace since I've to tear down the front of the car to get access to this engine cover and remove it. The plastic had warped/disintegrated. Stupid plastic. My car is a A7 3.0TDI but it's the same pretty much

This is the plastic flange with the engine cover

https://www.ebay.fr/itm/224734409473

[SaVAGeSoot]

I'm fairly versed in both the CNRB and CPNB....
Here's are docs from my model year that will help others see\visualize most of what's being discussed here.
There are also SSPs covering these models which you should become intimate with.
Hope these help

2014 A6/S6 Quick Reference Specification Book
Audi - The Second Generation 3.0L V6 TDI Engine
2014 Touareg Quick Reference Specification Book
VW - The 3.0L V6 TDI Engine (Generation 2)
2014 Q7 Quick Reference Specification Book

[Avantly]

I'm fairly versed in both the CNRB and CPNB....
Here's are docs from my model year that will help others see\visualize most of what's being discussed here.
There are also SSPs covering these models which you should become intimate with.
Hope these help

2014 A6/S6 Quick Reference Specification Book
Audi - The Second Generation 3.0L V6 TDI Engine
2014 Touareg Quick Reference Specification Book
VW - The 3.0L V6 TDI Engine (Generation 2)
2014 Q7 Quick Reference Specification Book

If you want to talk about TSB's/SSP's... Maaaan this sump leak really chaps my back side xD
Have you done the sump leak repair? I can't decide whether to pull the transmission and do it with the engine in the vehicle or just pull the engine and take a look at the timing guides at the same time. I'd like this thing to reach maximum lifespan.

Any experience with oil in coolant in VAG TDI's? From what I saw when I drained the oil, a small amount of coolant made it past the rings into the oil. I am guessing somewhere around 100ml max. Most of my oil in coolant (that made it past the rings) experience dates to older GM's with their intake gasket/plenum issues. Wondering if I should just pull the engine and take a look at the bearings while I'm also looking at the timing guides. It seems that finding spare CNRB's is going to be quite hard in the future.

[Avantly]

Another coolant leak that's maybe not as common or maybe it is. It's the plastic cover/flange that's bolted on the backside of the big front engine cover. It connects to the oil cooler with a small rubber hose. It happened to me a couple of months ago. All of a sudden on my way home from work, the coolant warning sounded off and told me to shut off the engine. Had to tow the car home. There were tons of coolant in the valley and my first thought was the oil cooler. I stripped it down and replaced all the gaskets on my way there. Pressure tested it and it still filled up the valley with coolant. Had to strip it down again. This time I filled up the coolant with everything out of the way and I saw a stream of coolant coming from the bottom of this plastic cover. A PITA job to replace since I've to tear down the front of the car to get access to this engine cover and remove it. The plastic had warped/disintegrated. Stupid plastic. My car is a A7 3.0TDI but it's the same pretty much

This is the plastic flange with the engine cover

https://www.ebay.fr/itm/224734409473

I was just staring at this thing a few hours ago and wondering how long it was going to last. Ugh. I guess I should buy a spare before they become unavailable and I have to cut one out of aluminum :-/

[SaVAGeSoot]

If you want to talk about TSB's/SSP's... Maaaan this sump leak really chaps my back side xD
Have you done the sump leak repair? I can't decide whether to pull the transmission and do it with the engine in the vehicle or just pull the engine and take a look at the timing guides at the same time. I'd like this thing to reach maximum lifespan.

Any experience with oil in coolant in VAG TDI's? From what I saw when I drained the oil, a small amount of coolant made it past the rings into the oil. I am guessing somewhere around 100ml max. Most of my oil in coolant (that made it past the rings) experience dates to older GM's with their intake gasket/plenum issues. Wondering if I should just pull the engine and take a look at the bearings while I'm also looking at the timing guides. It seems that finding spare CNRB's is going to be quite hard in the future.

There was a TT for the upper pan ...
It would be a massive job, so make sure that it is indeed leaking, and that it's leaking enough that you want to address it.... try re-torqueing first.
I doubt you can do it leaving the engine in, and realistically, if you're going in that deep, you might as well refresh the TC stuff regardless of being needed.... changes are that the upper covers are already seeping if not leaking by now.
CNRB - Engine Oil Leak from Oil Pan or Transmission (Bellhousing)Area

I don't know what kind of mileage you've got or what OCIs you're using, but you can get an idea of TC drive condition by evaluating your cam phase at full warm idle....

IDE00182 Camshaft adaptation intake bank 1: phase position

I've got a pretty good sample data collection on the Touareg forum where I've been tracking values trying to gain some knowledge about the potential "tell tale" signs of doom.
Check it out if you care.
3L TDI (T3) CATA / CNRB - VCDS chain stretch

I wouldn't worry about the coolant into the oil, unless you really have a reason to... low oil pressure, knock, some other sign.... unless you ran it like that long and hard, you should be ok.

[NorthernGTI]

There was a TT for the upper pan ...
It would be a massive job, so make sure that it is indeed leaking, and that it's leaking enough that you want to address it.... try re-torqueing first.
I doubt you can do it leaving the engine in, and realistically, if you're going in that deep, you might as well refresh the TC stuff regardless of being needed.... changes are that the upper covers are already seeping if not leaking by now.
CNRB - Engine Oil Leak from Oil Pan or Transmission (Bellhousing)Area

I don't know what kind of mileage you've got or what OCIs you're using, but you can get an idea of TC drive condition by evaluating your cam phase at full warm idle....

IDE00182 Camshaft adaptation intake bank 1: phase position

I've got a pretty good sample data collection on the Touareg forum where I've been tracking values trying to gain some knowledge about the potential "tell tale" signs of doom.
Check it out if you care.
3L TDI (T3) CATA / CNRB - VCDS chain stretch

I wouldn't worry about the coolant into the oil, unless you really have a reason to... low oil pressure, knock, some other sign.... unless you ran it like that long and hard, you should be ok.

Solid info. Ill have to try that with my car and see where Im at. I get a bit of rattle(maybe 1-1.5 sec) especially the last couple cold days here.

[Avantly]

Good info on the thread you linked to, NorthernGTI! Will definitely read all of that. This one is still nice and quiet on startup (even at -6 degrees the other day lol) but I will definitely watch the values.

The sump on this thing is leaking pretty bad, it started a few years ago and now it leaves a ~200mm puddle on the concrete every time you park it so it's definitely time to address it when I can.

I figured that due to the mileage I'd just pull the engine, go over the whole thing, and at a minimum put new chain guides and tensioner in it. This one suffered a ~90% (or greater) SCR restriction due to adblue injector crystallization a while back and when that thing got home after those symptoms appeared (while on a freeway trip) the turbo temps were pretty insane so I'd really like to just go over the whole engine, pull injectors and inspect/test, etc. Despite past problems it just runs fantastic and I'd like to keep it that way!

[Avantly]

I just wanted to update this, it's been more than 2 weeks with the EGR cooler gone, zero coolant usage and engine seems very happy even on the cold starts. Glad I caught this in time.

[SaVAGeSoot]

engine seems very happy even on the cold starts.

What you removed wouldn't have any impact on cold starts... it would only impact the "warm up" to full operating temp.

[Avantly]

What you removed wouldn't have any impact on cold starts... it would only impact the "warm up" to full operating temp.

I was referring to concern that the coolant which made it into the intake over a ~2 week period could have had some detrimental effect to the pistons... I've seen coolant cause galling of the pistons, and the galling then causes rings to stick in which = smoke/compression issues, increased friction between piston and wall which stretches the big end of the rod until one tries to leave the chat, etc... It wasn't that much coolant but I'm generally paranoid any time coolant makes it into the intake xD

[SaVAGeSoot]

I'm generally paranoid

I always use injector deviations at full warm idle to quickly judge if there's anything that I should investigate further in any of the pots.

[Avantly]

I always use injector deviations at full warm idle to quickly judge if there's anything that I should investigate further in any of the pots.

If there was galling of the piston, but not affecting the rings, I am not sure that should affect deviations at all? My experience is that when you get galling on the skirts it just stresses the rod end until it breaks. Granted I haven't seen this in a 3.0TDI but I've seen it in plenty of other engines!