VW TDI pistons - design flaw or a feature?

Hello everyone.

A friend of mine who lives in Germany and drives at autobahns quite often says that these TDI engines burn oil like crazy at high RPM. E.g. you can burn a liter of oil in 2 hours @ 3500 RPM.

Analysis shows that TDI piston design may be contributing a lot to that: theere are no internal oil drain holes in the groves where oil separation rings are located. What is more, there are no external channels for oil drainage there too.
Operation at high(er) RPM results in oil bypassing the oilrings, compression rings and getting burned simply because once the oilrings scrape the oil off a cylinder wall, there's nowhere it can drain so that some oil manages to bypass the rings.

We examined quite a few other European brand diesel pistons and ALL of them had either oil drain holes or external oil drain channels there.

Then there came a theory that this may be done on purpose - to lubricate the cylinder walls and compression rings at high RPM to avoid excessive wear on the engine.

Any ideas, comments?

Would really love is experienced people such as Pete (Drivbiwire), Frank (Franko6) and others would chime in with their opinion.

Thanks!

This comes off as a taunt and I will not rise to the bait.

Although I have my facts and opinions, I am most often required to keep them to myself.

franko6 said:

this comes off as a taunt and i will not rise to the bait.

Although i have my facts and opinions, i am most often required to keep them to myself.

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rotflmao!!

I'm not the experienced* automotive expert you're hoping for but a
very likely path for the oil into the combustion chamber is the CCV.
At high rpm there is a lot more blow-by to entrain oil into the intake.

*Shoot, I just remembered that I turbocharged my first car, a N.A.
Corvair, in 1970. Maybe I'm more experienced than I thought.

This is news to me, as on this side of the pond VAG diesels are generally pretty frugal with oil use. Now their gasoline engines, on the other hand....

And FWIW, your "friend" should look closer at the pistons, as there are clearly drains for the oil ring grooves.

Any pics of the drains? We both have inspected the pistons (PD engine) and did not notice any meanwhile on other car makes diesel pistons they were obviously seen.

Thank you.

Oh, sorry, you said PD.... I have only ever even seen one PD piston, and didn't have much reason to stare at it (I never really have much of a reason to go into the bottom end of one).

The ALH piston I have here in front of me has four drain grooves in it, two on each side of the piston near the wrist pin opening. The PDs are not like that I take it? Which PD, all of them?

My PD is about to cross 200k miles, RC1 since 80k miles, and it uses maybe a half liter of oil at most during its 10k mile service interval, pretty much the same as it has since new.

Yes, PD piston. This is what my friend has got and experiences oil consumptions at sustained high speed, high RPM driving only. He says that once RPM drop to normal, consumption goes back to absolute zero. So now I'm a bit confused if it's CCV or piston rings.

ALH pistons are different. I used Google to find some pics of it and the drain grooves are clearly visible.
We were examining 1.9 TDI-PD piston. I don't have the piston here neither made pics of it but here are some in fleabay:
1) https://www.ebay.com/itm/PISTON-VW-...448708?hash=item5458770804:g:PuQAAOSwUlxaOR6Y

2) https://www.ebay.com/itm/Audi-A3-8P...704270?hash=item1c81057ace:g:r84AAOSwd4tTuuf-

3) https://www.ebay.com/itm/VW-GOLF-V-...234258?hash=item1edbf437d2:g:oD8AAOSwaVRaqVv3

Upon quick look you will realize what is missing there. And no, there are no drain holes under the ring itself (inside the groove), if you ask. That's why I'm surprised.

Not telling TDI is an oil burner like TSIs are but seems that the bottom end of these engines don't like high RPM.

Would be interesting to examine a TDI-CR piston if something has changed in the design but there are no trashed CR engines around Taking a quick look at the pics from the net doesn't look too promising

We have lots of CR engines smashed flat in scrap heaps.

The crankcase breather by design scavenges as RPM is increased, so I suppose it is possible that sustained high RPM could cause the breather system to scavenge *too* well. I really have no data on that. I'd be curious to see what qualifiers this person has applied for "high RPM", and "sustained driving" and "high oil consumption" too.

My PD only needs 2500 RPM to cruise at 80. I've cruised for maybe 10 minutes at a stretch at about 100, but around here there just is not enough road to do this on without coming across traffic that is moving slower, and since we DO have speed limits in conjunction with some really bad left lane camping people, it is hard to apply any of this to us.

3500 RPM.... I'd REALLY be moving, and am 100% certain I could not do that straight anywhere around here for a solid 2 hours. But boy, if I could, I'd be happy to add oil to the engine as necessary.

This whole deal sounds like much ado about nothing, to me.

He reports the person loses a Liter in 2 hours at 3500. WAG that's 135 mph or a Liter in 170 miles. Not sure why they think it's a piston defect, but somethings not working right.

For what it is worth, the ALH in my Vanagon is spinning at about 3075 RPMs at 70 MPH (Vanagon gearing). So, on two road trips, about 11,500 miles each, in about 31 days each, it took less than a quart of oil on each trip to stay topped off (pulling a camper too). Also, it has an E-vac system which may "pull" more oil from the CCV system than what would normally be blown out.

I agree with BobnOH's assessment...

If he's geared the same as oil's, at 3500 he'd be doing 112 mph.

I agree with the aboves.

Henrick, is this one guy's experience or are you saying it's typical of German TDI owners?

KLXD said:

Henrick, is this one guy's experience or are you saying it's typical of German TDI owners?

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I'll try to provide some details I know. If something more is required, I can ask the person for more details - not a problem.

This is that particular guy's experience.
There is no data regarding any other drivers experience in Germany.
The driving carried out ir on one of German autbahns. I think there are no speed limits there.
Driving involves high speed, high RPM with some natural slowdowns due to traffic conditions.
Car is VW Golf Mk5.
Engine is 1.9 L TDI-PD, code BKC.
Gearbox is GQM, 6 speed. Runs ~108 km/h indicated at 2000 RPM in 6th gear.
Mild ECU tune. Turbo, injectors are not upgraded.
The driver himself has pointed that the pistons may be the root cause of excessive oil consumption at higher engine speed.
Engine does not consume oil in city driving or driving at lower RPM range.

Sounds like an isolated incident and he's got some problem.

My backada napkin computering makes that about 115 mph.

This reminds me of my younger days riding a Z2 which was a 750 version of a Kawasaki Z1 which as all should know was a 900cc. Kaw never brought them into the US so the speedo was in kph. After taking my girlfriend on it for the first time she asked in awe "were we really going 110 miles an hour". Had to disappoint her that it was only about 65.

Used to do the conversion in my head using .6 times kph = mph which was a little low.

So this is anecdotal, and hardly worth the thread. Got it.

Back to our regularly scheduled motoring....

Henrick said:

Hello everyone.

A friend of mine who lives in Germany and drives at autobahns quite often says that these TDI engines burn oil like crazy at high RPM. E.g. you can burn a liter of oil in 2 hours @ 3500 RPM.

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You used the word "engines" in plural, so I'm assuming he has driven several, and they all did this? Or is he generalizing, based on one car?

Not sure if he is generalizing based on one car.
You seem to be picky about the words.
I have just pointed a fact with a question in the 1st post. Why doesn't anyone want to discuss about the fact itself rather than the exact person, his driving style and engine?

Question is can this particular piston design contribute to oil burning past the piston rings or not?

We are picky about words, as the devil is in the details as they say. In answer to the original question I do believe that lack of oil drainage from the rings can contribute to oil consumption. I remember cleaning the drain holes on many an oil burning Honda re-ring as they were plugged with carbon.

What no one has proven yet in this post is the fact that drain provision has been omitted on these engines. I have seen only ebay pictures of pistons with the rings intact. Many manufacturers cut a slot in the oil ring groove to the inside of the piston to allow drainage. I have cleaned many of those out on re-ring jobs too. I am reasonably sure that if you got actual hands on with a PD piston you will find the drainage slots behind the oil rings as is very common.

I agree with all the others too, that one person's comment is not necessarily fact. It is like saying "all Chevy small blocks burn oil" which we all know is a factual statement.

Henrick said:

A friend of mine who lives in Germany and drives at autobahns quite often says that these TDI engines burn oil like crazy at high RPM. E.g. you can burn a liter of oil in 2 hours @ 3500 RPM.

Click to expand...

Come on, there is no way to interpret this except that he is saying they all do.

A lot of discussion followed.

These engines have been around since '98 in the States and longer in Europe and this is the first such generalization on oil burning that I've seen in my few years of reading this Forum.

Henrick said:

Then there came a theory that this may be done on purpose - to lubricate the cylinder walls and compression rings at high RPM to avoid excessive wear on the engine.

Click to expand...

As for discussion I'll add my 2 cents on this point.

I doubt this is the intent. The point of the oil rings is to remove excess oil from the cylinder walls. I doubt there is a lack of oil there at 3500 rpm such that the oil rings are designed to ad more.

Henrick said:

Not sure if he is generalizing based on one car.
You seem to be picky about the words.
I have just pointed a fact with a question in the 1st post. Why doesn't anyone want to discuss about the fact itself rather than the exact person, his driving style and engine?

Question is can this particular piston design contribute to oil burning past the piston rings or not?

Click to expand...

We question the validity of the "fact" concerning the piston design. We recognize the fact that the persons car used a Liter of oil in a very short time.
But hey, no harm bringing it up for discussion, kind of what forums are for.

I reconsidered. I do have an opinion. I have a feeling this oil issue is something that can be isolated to an individual and their driving practices, not a group, unless you mean a group that thinks they need to drive at 240kmh for extended periods of time.

I can say that engines that have been driven excessively hard will anneal the rings and excessive blowby causes the oil control rings to become fouled. That will lead to excessive oil usage.

At that point, the rings should be replaced and the cylinder dimensionally checked and repaired, if necessary.

Also, we have rings and pistons that are designed for extreme load. Larger ring drop keeps them out of the heat. Diamond impregnated performance rings we sell reduce drag 6-8% and the oil control ring is dlc coated for additional wear protection.

Oil-galley cooled pistons, water/meth injection, large CR drop, and porting with the idea of EGT drops as a goal would certainly help. And carefully set injectors... real careful.

If a stock engine is pushed past it's reasonable limits, failure is imminent. You can't expect a 100hp engine or even a 150hp VW diesel engine to keep up with a BMW, Porsche or Mercedes Benz, let alone the exotic cars.

A lot of interesting ideas, thanks guys.
I think more investigation needs to be done on that particular engine. E.g. somehow to check how much oil goes through CCV. Need to think of a setup (probably a hose and a bottle) to check that...

I think these are to collect oily vapor-
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