Multiple oil ( & coolant) leaks, raised crank-case pressure?

[ChrisP]

Hi Y'All,

This is by way of part follow-up to my last 'C7 vs C8 Audi A6 Allroad purchase?' posting, and an appeal for some info as to the likely causes of raised crank-case pressure in my old soon-to-be-disposed-of 2015 218HP C7.  

After having the 130,000 mile 'AdBlue System Fault' advisory confirmed as a faulty (low pressure) AdBlue pump at an Audi Main Dealer, who proceeded to replace the pump and reflash the ECU software, thus sorting the problem satisfactorily, I took the car to a well-thought-of 'Audi Specialist' about 10 miles away to look over a chronic recalcitrant oil leak that the local heart-sunk village garage had failed to sort, despite replacing a cracked (plastic) offside rocker cover, and having twice refitted the front crankshaft seal over the last twelve months. They are a great outfit who previously kept my pair of mid-1990's BMW 525iX's on the road for the last 7-8 years of their lives.

The independent specialist confirmed multiple high-volume oil leaks, including the front crankshaft seal (again), around individual bolts attaching the sump, and at the head gaskets on both sides, where also leaking coolant. They diagnosed (-by implication) an underlying elevated crank-case pressure, felt the necessary repairs uneconomic, and recommended that the said sad machine be released into the trade through one of the discounted online high volume purchasers, caveatemptor.com, and that I clench my teeth and take the hit.

Two things amazed them: (1) the car drove very well, the engine remarkably smooth and responsive (-confirming my own impression of great poke and economy) and (2) its history of having thrown no less than 5/6 of its diesel injectors over this last four years, each having required new retaining bolts, seals and helicoils in the Alu head. Never had they seen such a thing in any 3.0TDI-engined context previously.

They attempted to explain the raised crank-case pressure with reference to the thrown injectors, and their gunk-blocked by-pass channels, but I failed to grasp the physics.

In the meantime, my needing a replacement Allroad, I bought a 2018, 26,000-mile C7 A6 3.0L TDI, with tech-pack and a few more (ie 268) HP, freshly serviced with a 12-month MOT. 

Looking ahead, I remain fearful. How might I avoid or mitigate the same (unknown!) predisposing problem in the new motor? Famous causes of pathologically raised crank-case pressure include disrupted piston rings, and blocked/choked PCV's. However, with so smooth a free-revving and pokey engine, and great fuel economy, surely the rings could not be broke? And looking into the PCV issue, in the 3.0L TDIs, the PCV function is apparently integrated into the plastic rocker-cover, one of which was replaced for a crack, (-originally suspected as the cause of the oil leak), some 12 months back, and the other declared patently innocent just last month.

Help me understand, please!

Than you,

Chris

 

[Optimus]

Lots of information to digest and it’s hard to pin point exactly the issue(s) in your post.

with regards to seals whether they are bead or gasket or ring. For as long as I can remember manufacturers of all makes and models have always stated that these are perishables and after a certain amount of mileage or time (typically 100k or 8+ years) these will fail and require resealing as of when identified.

 

Bases on your description this is from my point of view considered normal wear and tear that won’t be avoidable. 

[ChrisP]

Thank you. Apologies for lack of clarity. I guess what I'm seeking are answers to the following questions:

(1) why the car should have thrown 6 diesel injectors (#6 now puffing too!) / 130,000 miles

(2) whether these injector problems may have somehow resulted in raised crank-case pressure, in the absence of either (a) cardinal signs of piston ring damage (ie irregular running, loss of power and poor fuel economy) or (b) evidence of PCV blocking, either of which are frequently cited as the 'usual causes'. And if the injector problems can be indicted as a cause of raised crank-case pressure, how might this occur? What is the physics?

The Audi specialist was unwilling to countenance the notion that so many oil leaks and such heavy lower engine compartment oil contamination were mere coincidence. He took the view that they could not have occurred without underlying predisposing cause (- ie raised crank-case pressure).

Thanks,

Chris

[Magnet]

Hello Christopher,

Culprit likely to be worn piston rings, allowing compression to feed back into the crankcase. Used to check for that by partially removing the dip stick and observing any back pressure. 
What is the maintenance history of this vehicle? 
Kind regards,

Gareth. 

[ChrisP]

Hi Jason,

Thanks. Neither injectors, bolts or seals  injectors were touched or serviced before they first blew, or started to leak, and in the case of those that blew out, the steel retaining bolts stripped their retaining sockets in the Alu head/block, thus then requiring helicoil fixation. Initially, two bolts were unfortunately reused, but when I read around the subject and appreciated the implications, I had the garage replace with new and retorque to spec, and this approach was subsequently used for all the others. New copper seals were used on each occasion throughout. So we still have no explanation for so many injectors coming loose and requiring resetting.

 

Hi Gareth,

Thank you. The engine has been serviced to manufacture's spec, with regular oil changes until this last twelve months, since  when the same has been achieved by continuous topping up necessitated by the leaks (-in course of trying to fix which one cracked rocker cover has been replaced, and a front crank-shaft seal three times, latterly using the Victor Reinz (disposable) special setting tool). In respect of your suggestion re worn piston rings, as the likely cause of raised crank-case pressure, there is no dipstick on these vehicles to investigate in the way you recommend, simply the bayonet-fit top-up cap. And as I mentioned, there is no apparent loss of power or fuel economy, and the engine-running seems entirely smooth, the tachometer showing no rpm hunting.or dancing about. However, my reading of the Rheinmetall website this pm (https://www.ms-motorservice.com/int/en/technipedia/sealing-problems-and-piston-ring-damage-889) does suggest that an injector leak may cause diesel deposition on rings and cylinder walls, displacing lubricant and rapidly accelerating their wear. This begs the question (-as to why so many injectors should be thrown) which I posed to Jason... 

[Magnet]

Many thanks for the additional information Christopher. Apologies for the confusion over the dip stick - did mention ‘used to’. Oil dilution may indeed be the reason why this engine may have suffered from premature bore/ring wear. 
Sorry to be pedantic and ask more questions, but ‘serviced to manufacturer’s spec….’ Would this have been on a Longlife schedule by any chance, where the oil was changed c every 18k? If so, this bad experience may point to the benefits of at least annual changes, and dare I say every 6months, where oil dilution raises its head. 
Kind regards,

Gareth. 

[Stevey Y]

On 2/19/2024 at 10:03 PM, ChrisP said:

Hi Y'All,

This is by way of part follow-up to my last 'C7 vs C8 Audi A6 Allroad purchase?' posting, and an appeal for some info as to the likely causes of raised crank-case pressure in my old soon-to-be-disposed-of 2015 218HP C7.  

After having the 130,000 mile 'AdBlue System Fault' advisory confirmed as a faulty (low pressure) AdBlue pump at an Audi Main Dealer, who proceeded to replace the pump and reflash the ECU software, thus sorting the problem satisfactorily, I took the car to a well-thought-of 'Audi Specialist' about 10 miles away to look over a chronic recalcitrant oil leak that the local heart-sunk village garage had failed to sort, despite replacing a cracked (plastic) offside rocker cover, and having twice refitted the front crankshaft seal over the last twelve months. They are a great outfit who previously kept my pair of mid-1990's BMW 525iX's on the road for the last 7-8 years of their lives.

The independent specialist confirmed multiple high-volume oil leaks, including the front crankshaft seal (again), around individual bolts attaching the sump, and at the head gaskets on both sides, where also leaking coolant. They diagnosed (-by implication) an underlying elevated crank-case pressure, felt the necessary repairs uneconomic, and recommended that the said sad machine be released into the trade through one of the discounted online high volume purchasers, caveatemptor.com, and that I clench my teeth and take the hit.

Two things amazed them: (1) the car drove very well, the engine remarkably smooth and responsive (-confirming my own impression of great poke and economy) and (2) its history of having thrown no less than 5/6 of its diesel injectors over this last four years, each having required new retaining bolts, seals and helicoils in the Alu head. Never had they seen such a thing in any 3.0TDI-engined context previously.

They attempted to explain the raised crank-case pressure with reference to the thrown injectors, and their gunk-blocked by-pass channels, but I failed to grasp the physics.

In the meantime, my needing a replacement Allroad, I bought a 2018, 26,000-mile C7 A6 3.0L TDI, with tech-pack and a few more (ie 268) HP, freshly serviced with a 12-month MOT. 

Looking ahead, I remain fearful. How might I avoid or mitigate the same (unknown!) predisposing problem in the new motor? Famous causes of pathologically raised crank-case pressure include disrupted piston rings, and blocked/choked PCV's. However, with so smooth a free-revving and pokey engine, and great fuel economy, surely the rings could not be broke? And looking into the PCV issue, in the 3.0L TDIs, the PCV function is apparently integrated into the plastic rocker-cover, one of which was replaced for a crack, (-originally suspected as the cause of the oil leak), some 12 months back, and the other declared patently innocent just last month.

Help me understand, please!

Than you,

Chris

 

Hi if you want to see what a blocked PCV will do look at the late Ford Transit, my fellow cab driver has a 20 plate and in short was suffering the same symptoms as you he even murdered the DPF and EGR Valve and multiple crankshaft seals before they narrowed it down to the PCV which is integrated in the rocker cover and had been changed 40k ago, any bore wear will cause excess crankcase pressure which would normally escape through the PCV, Positive Crankcase Ventilation system, if it can't escape the gas will take the path of least resistance, seals, back up the bores and ultimately destroy the Turbo as it will cause oil feed fluctuations to that unit, gone are the days when a tube venting into the world and filled with wire wool to stop the oil getting out will do.

Steve.