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I just finished the oil cooler servicing but thought the leak looked like it was coming from the oil cooler everything was in great shape. Turns out someone had serviced the cooler. I should have guessed that when the bolts would not come off as I have done this job before and it was obvious they were not at factory torque specs. Impact wrenches are a great convenience for mechanics or should I say for the first mechanic, not the one coming second to undo the massive over tightening. Ended up replacing all 5 bolts as there wasn’t much left of them when I barely got them off.
After injecting some Radiator/Coolant Dye I have traced the leak to the rear of the engine.
Seems the leak is at #18 & #8 and is leaking down the pipe and making it look like oil cooler leak.
I have been able to find the part #8 which is the hose but not the clamps (#18).
Has anyone replaced the parts at this junction? It looks impossible to get in there without removing a good deal of air intake and other surrounding hosing.
Although the oil cooler job is grueling it is relatively straight forward. Getting back into the rear of the engine to fix this leak looks difficult because even if I successfully remove and replace everything that is in the way getting the hose clamps on tight down in that hole looks like a real challenge. Which make explain the leak as they are not factory clamps.
The leak is not coming from #8 and #18 It just looked like that.
Also the diagram I posted that is from Audi and supposedly for the engine that is in the 2001 S8 is also incorrect.
The rear coolant pipe in the diagram has the cross bar and the drop down large pipe to the radiator and the port on top for the sensor but is missing a port.
This missing port that connects straight onto the back of the opposite of the tube the goes to the radiator is where the leak is coming from and it is dripping down onto #8 #18 and running down that pipe and dripping out the back of the car.
It’s amazing how there is no fluid at the leak source. It perfectly drips onto #8 with sinister precision and then down and out. Masking the source. The fluorescent dye and light and crawling under the car and being persistent were the only way to find this.
I have contacted the mechanic that did my engine rebuild.
I'm considering this a failure of the rebuild.
I can't even imagine how to fix this leak or I would just fix it and not bother the mechanic but I can't find any guidance on this issue online.
I doubt anyone has fixed this problem because:
1) it’s probably rare and would only happen to an engine that has been removed and replaced or rebuilt
2) it is very hard to detect and would have probably been overlooked.
If someone has installed a 40V engine in a D2 and has guidance on getting this pipe in without it leaking I would love to hear it.
The pink circles are drops of fluid the arrow point to the pipe
Last edited by omarcarbomb; 01-04-2017 at 10:00 AM.
That joint has an o-ring to seal it in to the pipe coming off the front of the right hand head. The only plausible reason for it to leak is if the o-ring got pinched when it was reassembled, or the o-ring wasn't replaced during the rebuild, possibly because its not actually shown on the diagram.
Access to that pipe with the engine in is going to be a challenge as the SAI stuff is all in the way, but in theory you don't need to actually remove it - only pull it back about an inch to get to the o-rings. You'll also need to replace the two o-rings in the flanges on the back of the heads. The flanges are held on with M6 socket-head bolts (two on each head) to which it should be possible to access from above. You'll need to take the inlet pipework off, including the throttle body boot (that should just push to the side). Once the M6 bolts are out the pipe should wiggle backwards just enough to change the o-rings. It'll normally be pretty tight in the socket which is leaking, but if its been in bits already it might come out ok.
Putting it back in, lubricate with dish soap so it doesn't get pinched.
The o-rings for the flanges are both N90560701 to 4D-Y-007000, or N90912501 from 4D-Y-007001. I will do some digging to see if I can find the number for the missing one. Worst case, I have an engine in bits at the mo so I can measure the groove for it and work out the size from there.
No inlet manifold here obvs, and this one has the SAI stuff deleted the same as mine. You can just about see the alloy socket in to which the leaking pipe fits, to the right of the green temperature sensor.
This one shows just how much stuff is in the way:
Not going to be a fun job I'm afraid
Last edited by MikkiJayne; 01-04-2017 at 11:32 AM.
01-02-2017, 10:56 AM
Rear Coolant pipe leak
or should I say for the first mechanic, not the one coming second to undo the massive over tightening. Ended up replacing all 5 bolts as there wasn’t much left of them when I barely got them off. 
