How to find the cause of oil consumption without replacing half the parts randomly?

[WeekendDriver]

It's been 1400 km since I've changed the oil, and now the oil level is ~33% between the low and high marks on the oil probe stick. I'm guessing that amounts to ~1.5 L oil consumption (considering the level was initially a tad over max), or ~1 liter per 1000 km. Which is a whole LOT.

I've visited a local service station. We took out the spark plugs and found out there's oil on their thread. There's also a lot of visible snuff (is that the word?) on the piston surface.
They also took off the turbo intake pipe in order to move the rotor by hand, and there seems to be a lot of longitudinal play. The amount of transverse play remains undetermined.

Basically, we've found a couple problems but I still have no idea what parts I need to replace and what parts can be left alone for some time. I'm on a budget, and in general I don't like replacing operational parts that can last 10 more thousands km.
The service guys told me the turbo is dead and needs replacement ($500+), and the engine's head needs overhaul (~$400).

What I intend to do:
1. Visit another service. Ask them to have a look at the crankcase ventilation system.
2. Take off the piece of pipe between the turbo and the intercooler. See how much oil there is - i. e. how much the turbo throws to the intake part of the engine.

Questions:
1. I've been told that if the turbo was throwing 1 liter of oil per 1000km directly at the exhaust manifold, I would see smoke coming out of the tail pipe. Even with catalytic converter still installed, which I do have. Is that true?
I have never seen any oily-looking (bluish) smoke coming out of my car, only minor amounts of light white smoke, more like water vapor.
Consequently, I've been advised to not replace the turbo just yet because it doesn't seem very dead. It makes no sounds that I can hear, and I can feel the turbo spool - the car leaps forward alright once I have 2300-2500 RPM on the tachometer and I press the accelerator pedal. I mean, I wouldn't know if it leaps just like a perfectly working 1.8T should, or if it's worse, but it does pull.

2. Can the crankcase ventilation system be tested without disassembling it and checking every valve and pipe?
I've just recalled the oil cap test that I will perform later today, but is it definitive?

3. How else can I find the reason for the oil consumption? Especially in the cylinder head part. Oil on the spark plugs clearly indicates something's wrong there, but what? Also, how much of an oil consumption can the head possibly account for? I'm not really looking forward to spending $500 on the head rebuild - only to find out that my oil consumption is down from 1.0 to 0.8 L/1000 km.

The car has 209 000 km, or 130 000 miles, on it. It might be of note that I drive very non-aggressively, and pretty much never spin the engine past 2300-2500 RPM. 99% of the time I switch to the next gear as soon as I reach 2000 RPM (as per the recommendation in the owner's manual). That's the mode car spent at least 90% of those 1400 km since the oil had been changed.

Sorry for noobish questions. I've just got the car recently, it's my first, and am just learning all this stuff.

[StriktlyAudi333]

I would start simple my friend. The car is over adjusting for something, that's why it's happening. So, starting off with what is the least expensive, clean your throttle body and either clean or replace the MAF. It's common for those to cause the car to run lean or rich. I would also get new plugs and make sure you torque them at spec just to make sure you crush the washer completely to prevent a vacuum leak

[Spectre1130]

I would start simple my friend. The car is over adjusting for something, that's why it's happening. So, starting off with what is the least expensive, clean your throttle body and either clean or replace the MAF. It's common for those to cause the car to run lean or rich. I would also get new plugs and make sure you torque them at spec just to make sure you crush the washer completely to prevent a vacuum leak

Oil consumption. Not fuel consumption.

When you say longitudinal and transverse play on the shaft what are you talking about? There is radial and axial play. Radial is wiggling it side to side, some is normal it shouldn't contact the edges of the housing. Axial is in and out, you shouldn't have any. If you have any axial play your turbo is going bad/already bad. This is a test of the bearings.

Answers to questions:
1. Blue smoke is oil burning. It's up to you if you want to have to be filling up on oil and changing gas. The turbo bearings are bad when it makes a dentist drill sound. Sounds like your seals could be bad and your bearings on their way out. You can easily get a junkyard turbo and rebuild it in your spare time.

2. You cant test it 100% but you can do the oil cap test which I'm assuming is see if your oil cap is pushed off with crank case pressure? If it pushes off you definitely have an issue with your PCV.

3. I don't think you should have head leakage. I've never seen it in my cars which are all 150k miles and more. Oil on the plugs can be an indicator of oil just getting into your cylinders. Which can come from PCV problems, turbo problems, piston ring issues, old engine issues.

My money is on the turbo being old.

[WeekendDriver]

When you say longitudinal and transverse play on the shaft what are you talking about?

I meant to say my turbo has axial play. Along the shaft.

1. Blue smoke is oil burning.

I know that. I was saying I have NOT ever seen blue smoke coming out of my tail pipe (or much of any smoke, really), and yet I've been told I would definitely see some if the turbo was throwing oil into the exhaust manifold. So that basically says my turbo is not leaking oil into the exhaust, but I'm not sure how much of a reliable indication that is.

You can easily get a junkyard turbo and rebuild it in your spare time.

No one in my country can rebuild a turbo so that it lasts more than 20 000 km afterwards. I was strongly advised against rebuilding and towards getting a new one.
I could replace the cartridge but I've been told it can only be done if the housing has no cracks, and it almost always has cracks.

2. You cant test it 100% but you can do the oil cap test which I'm assuming is see if your oil cap is pushed off with crank case pressure? If it pushes off you definitely have an issue with your PCV.

3. I don't think you should have head leakage. I've never seen it in my cars which are all 150k miles and more. Oil on the plugs can be an indicator of oil just getting into your cylinders. Which can come from PCV problems, turbo problems, piston ring issues, old engine issues.

Thanks. I've been told oil on the plug absolutely could not have come from the turbo. But it could come from poor PCV, I assume.

Speaking of which. I unscrewed the oil cap, and it clearly indicates there's extra pressure in the crankcase. It's literally jumping up. It keeps doing that with less and less force up to 2000 RPM, perhaps even 2500. At 3000 RPM there's considerable suction.
Given my driving style, it means there is extra pressure in the crankcase 100% of the time. I suppose that's not normal? The cap shouldn't be jumping up even at idle, should it? I think it might actually be important; if there should indeed be NO extra pressure in the crankcase even at idle, I'll make fixing this problem my top priority.

[Seerlah]

Oil in the combustion area is mosy times due to valve guide seals. Does not mean an engine overhaul. It means taking out came, lifters, and springs. Then you can get to the guide valve seals. Take off, replace, put things back together. It is a pretty in depth job, but not difficult to say the least. And a shop most def will take advantage of this situation and charge too dollar if they want.

With that being said, it probably isn't even the issue. Having burnt residue on the piston dome is completely normal. When valve seals leak, the exhaust smoke is content is like a dead give away.

I suggest you just change your valve cover gasket, cam chain tensioner gasket at same time, and pcv valve. And inspect for oil residue yourself. If you take pics of any oil residue you findx we most likely can tell you where the leak is just from where the residue is.

[WeekendDriver]

Thanks! I've been told the engine head overhaul is in order, which involves machining the head, among other things, and amounts to $400-500 (labor + parts). But I still don't know if it's the head or or the turbo that's the major oil eater (I have no doubts both do eat some, the question is which one eats more).

I have changed the valve cover gasket and cam chain tensioner gasket when I bought the car 1400 km (less than 1000 miles) ago, as well as the camshaft seal rings.

I will see if I can make a picture of the residue that covers the pistons. From what I've seen so far, it seemed to cover the whole surface of the piston pretty evenly (as much as I could see through the spark plug hole, anyway).

P. S. It might be of note I've been told there's exactly one liter of oil between MIN and MAX marks of the oil probe, which means my oil consumption is 0.5-0.6L per 1000 km, not 1.0.

[Seerlah]

What exactly is an engine overhaul? You may be about to be taken for a ride. And if you have oil on your spark plugs, your valve cover gasket is compromised. 1000 miles or not, accept it needs to be replaced again.

[WeekendDriver]

What exactly is an engine overhaul? You may be about to be taken for a ride.

Not the whole engine, just the head. But yeah, you might well be right and I'm not doing anything costly just yet.

Are you sure the valve cover gasket is the only possible source of oil on the spark plugs? Cause there are several valve-related parts that can leak oil, but I don't know the engine head design well enough.

[Seerlah]

There are others, but doubtful reasons.

1) Oil dripped down from on top of valve cover, past the ignition coil boots and settled on the plug
2) Spark plugs are loose and oil kicked back from the combustion chamber, where you suspect you are burning and not losing oil, then settled on the spark plug

Like I said, both highly doubtful reasons. May I ask, what brand gasket you used last time and who installed it?

Also, don't think too much about the carbon build up on the dome of the pistons. It is totally normal. Unless you see more than carbon build up, then be concerned. I still suggest to look into leaks. And of course turbo seals. If you plan to have a shop do the work for you, they can tell you anything and you may or may not believe it. But regardless, what they say to you will still influence your opinion. For example, only cylinder head component that can cause you to burn oil is your valve guide seals. But unless you are clearly burning it with results seen in your exhaust out your muffler, look elsewhere. Then they use words like "cylinder head overhaul" to basically scare you to spend money in fear of having your vehicle break down. Maybe I'm right, maybe I'm wrong. But it's still my opinion.

[WeekendDriver]

May I ask, what brand gasket you used last time and who installed it?

All work is being done by a shop. I bought Elring valve cover gasket (633.350).

As I mentioned, I have yet to see ANY oily smoke from the exhaust. There's no scurf on the muffler tip either. But where else can the oil go then? I mean, it either goes the intake side and burns inside a cylinder, or it goes the exhaust side and burns in the exhaust manifold. Or it simply leaks somewhere, but surely, 0.5 liter of oil leaking should have left some trace? I can't see any.

[Seerlah]

Look under your intake manifold.

[WeekendDriver]

I know where the intake manifold is, but am not sure how or where you're suggesting I should look. A little clarification, if you please? I suppose you mean looking for oil stains on the outside, beneath the manifold? Is that a common source of oil spills?

[Seerlah]

Just take a look. There is a lot of stuff going on under your intake manifold, like your oil cooler, oil filter, and pcv valve I suggested in my initial response to this thread for example.