Stubborn Oil Leak-- Informed guesses much appreciated

[aslusher]

Hello all,

I have been using the archives of this forum to make repairs on my A4 since I bought it April. The threads here have been so thorough that I haven't had a need--until now--to create one of my own.

I started with an oil leak on the rear of the engine. Passenger side, leaking down onto transmission. The car came with a faulty breather system (cracked tube going into oil filer housing), and I later noticed oil dripping from the valve cover area onto the exhaust. I first replaced the breather hoses with a kit from ECS, then did the valve cover gasket, cam chain tensioner gasket and half moon seal in one go.

After around 1500 miles, I got the oil min light. No more oil from valve cover, and I can't feel any around the CCT. Now I am scratching my head. I suspect possibly a seal on the EGR valve, numbers 22 and 21 on the diagram below. While I am back there, I am thinking I will try to replace as many potentially suspect gaskets as possible so that I don't have to do it again.. It is very difficult for me to see the source of the leak without disassembling the pile of valves and hoses on the back of the engine. Anyone have any ideas as to what else may cause this sort of leak? It would be nice to buy all the gaskets at once, and disassemble only once to do the replacements. Advice is much appreciated.

EDIT: I should note, I have a B6 A4 1.8T engine code AMB

[old guy]

The combi valve seals (21 and 22) would have nothing to do with an oil leak. Exhaust leak yes, but oil leak no. Are you still seeing an active leak from the back of the engine?

[aslusher]

Ah, thanks for the input. I am still finding my way around this engine, and am very much an amateur.

As I said, it is difficult to see much.

Before replacing the VC and CCT gaskets, I noticed the oil on the back of the engine / top of the transmission. I wasn't able to properly clean that oil off, and I assumed the heat would at least turn it more sooty (as has happened to the oil on the heat shield on the passenger side of the engine block). I still see the oil on the back of the engine, though, and it still has a wet appearance. I also located the downstream residue of that oil on the bottom of the engine (very wet, drippy) when I removed the sound absorber panels to change the oil. I guess the only option is to disassemble some of the hoses and valves and stick a mirror back there?

There definitely is also a small amount of oil coming from where the two parts of the dipstick tube meet, which I will be replacing soon as well. This is probably a contributing factor, but I was fairly certain that the amount of oil I have lost could not be coming solely from that location. Maybe I'm wrong? At any rate, the oil on the back and bottom of the engine is indeed fresh, and I have to believe that the majority of the issue lies there..

[old guy]

An oil leak large enough to loose a quart of oil in 1,500 miles would be fairly significant. You would probably see small puddles of oil wherever you park your car. You mentioned that you replaced at least part of the block breather hoses. If you have a defective check valve (or one installed backwards) it can cause a significant of oil to be consumed through the engine.

You can test your check valves by simply removing each vacuum line connected to the intake manifold one at a time and use an air nozzle to pressurize the line. Under no situation should you be able to blow air through any of the lines. If you can that would be an indication of a defective check valve.

[Luxus Panzer]

You can test your check valves by simply removing each vacuum line connected to the intake manifold one at a time and use an air nozzle to pressurize the line. Under no situation should you be able to blow air through any of the lines. If you can that would be an indication of a defective check valve.

Good to know😃.

SO air can only flow IN to the IM with functional check valves. Never air flowing OUT of the IM.

Do I got it ?

[old guy]

You got it.

[aslusher]

I see, thanks. Will test these asap. Tried to get some pics from behind the engine to better assess the leak, but that proved rather difficult..

[Luxus Panzer]

sweet, good simple test method

[aslusher]

So I began testing these check valves, and the first one I tested, the 3-way next to the suction jet pump, was faulty..I broke the nipple removing it as well.

I decided to pre-emptively purchase 3 new 2-port check valves (in addition to the 3-port I have confirmed to be faulty). I might have screwed up with a rash purchase though.. Are the 2-port valves interchangeable? Etka lists different part numbers for them, but to me they appeared identical, so I ordered 3 of these before realizing they do in fact have different part numbers:
https://www.ecstuning.com/ES2598293/
Will these work for all the valves, or did I buy three valves for one location?

Will likely also replace as many of the vacuum lines as I can as a part of this process. Any recommendations here? I like the idea of silicone, but have read mixed things on it..

Thanks in advance for any suggestions and insights

[CyberPMG]

Any oil in the belly pan? If so, take it off and leave it off for a day or two. put some cardboard under the engine on the ground to catch anything leaking. Should give you a general location where it is to help isolate where it is on/around the engine.

How do the spark plugs look? If they look oily, the spark plug gasket is likely leaking oil into the cylinders. Check exhaust for any smoke?

[old guy]

So I began testing these check valves, and the first one I tested, the 3-way next to the suction jet pump, was faulty..I broke the nipple removing it as well.

I decided to pre-emptively purchase 3 new 2-port check valves (in addition to the 3-port I have confirmed to be faulty). I might have screwed up with a rash purchase though.. Are the 2-port valves interchangeable? Etka lists different part numbers for them, but to me they appeared identical, so I ordered 3 of these before realizing they do in fact have different part numbers:

You are good. That particular check valve is used in multiple locations. There is also a larger version (06A133528D ) that is used in the block breather hose that connects the lower breather to the valve cover. There is only one of those.

[diagnosticator]

Any oil in the belly pan? If so, take it off and leave it off for a day or two. put some cardboard under the engine on the ground to catch anything leaking. Should give you a general location where it is to help isolate where it is on/around the engine.

How do the spark plugs look? If they look oily, the spark plug gasket is likely leaking oil into the cylinders. Check exhaust for any smoke?

This is not possible.

[aslusher]

Thanks to everyone for the help and suggestions. I tested all of the check valves, and found in the end that 2 were defective--the 3 port by the suction jet pump, and the 2 port by the n80 valve. Still studying the diagrams to understand if it is possible that either or both of these valves could have caused oil to be burnt.

In the process, I have made note of a small coolant leak around the CTS on the back of the engine. The mysterious oil source remains to be found..current (hopeful) theory is that the oil is no longer actively leaking, but was being burnt, and that the oil residue on the back of the engine is being remoistened by dripping coolant. I imagine worst case is probably a blown main seal..I will inspect the plugs for oil next and keep my fingers crossed.

Again, I appreciate the help. Will be sure to update as I make progress on this.

[aslusher]

This is not possible.

Why is that not possible?

Are you suggesting that the oil would be on the coil packs?