Final Horrifyingly Stupid Question - OCI?

whitedog

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Is anyone else seeing that the amount of FE in the oil is going up? What would the FE PPM be at 25,000?

I'm trying to understand why FE PPM / 1000 miles is relevant.
 

Bob_Fout

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whitedog said:
Is anyone else seeing that the amount of FE in the oil is going up? What would the FE PPM be at 25,000?

I'm trying to understand why FE PPM / 1000 miles is relevant.
Fe ppm/1K is the wear rate and is (IIRC) a more important number as long as total Fe also stays within a certain range.
 

Dimitri16V

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from what I know, friends of mine in Germany have TDIs , Audis in particular, the oil change is reminded by the computer and it always comes up around 30 -45 K KMs . BUT , that's using Castrol Long Life oil and they were given additional Castrol oil called Top off or something like that to replenish oil and its additives. that supplemental "oil" was only to be added to the oil when the level dropped.
 

whitedog

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How much metal is in the oil causeing damage is the important thing. How long it took to get there is pretty much meaningless, no?
 

Drivbiwire

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Fe/1000 miles tells you how well the oil is protecting the engine.

If the engine is only producing 2ppm of Fe at 3000 miles and the engine is still only producing 2ppm of Fe at 30,000 miles the oil is STILL performing optimally.

A lot of people look only at the total Fe, that only tells half the story. Looking at the total Fe and using the total miles driven to derive a rate of wear on a per 1000 mile basis gives you the complete picture.

Cars that have high soot loading (read chips, injectors etc) will almost always have higher Fe/1K wear rates due to the inceased soot and contaminants in the oil.

Installing an oil by-pass gives approx a 40% reduction in Fe/1k wear rates with no other modification! All you are doing is removing the larger particles and allowing the oil film and addtives to do their job.

I also want to make a point that the wear rates I am citing here are based on a standard oil sump volume. If you increase sump volume (adding a by-pass which increases the sump by 1 liter) you can throw off the data.

Example:

4 liter sump = stock (correction factor 1.0)
5 liter sump = Stock + Dieselgeek Bypass (Correction factor 1.25)

Using the above sump volumes:
If a stock sump has 50ppm no correction factor required.
If you have a Dieselgeek bypass multiply the total Fe by 1.25

Then using that corrected value compute Fe/1K data. That way regardless of sump volume you are reading a baseline number that is not thrown off due to dillution related variables which can be compared to any other 1.9L/2.0L TDI engine.

Lets say you want to compare a Cummins to the TDI, the Cummins uses a 14 quart sump (15.14 liters). The Cummins has a total Fe of only 15 in 10,000 miles. At first this appears low, right?

Using a correction factor of 3.785 (15.14/4) gives an Fe/1k in the Cummins of 5.6775 Which for the sake of the conversation is nearing the upper end of the acceptable wear range despite the low total Fe in the oil sump.

Make sense?
DB
 

whitedog

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But if your FE PPM is so high that it gets flagged, why would you want to keep it in there?
 

whitedog

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What does the wear rate give me a picture of?

If I have high iron, I want it out. Why should I care if it got there in 5000 miles or 20,000 miles?
 

Drivbiwire

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They flag oil without consideration of miles driven. They only look at total Fe...Thats not exactly a good idea.

Look at my Cummins example, the oil wasn't flagged but when I looked at the sample I told the owner that his oil will need to be changed at 15K due to increasing wear rates. Of couse he asked if 15ppm was high, I said no but when you take the dillution of the oil into account it was about double what is typically considered optimum.

DB
 

Drivbiwire

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whitedog said:
What does the wear rate give me a picture of?

If I have high iron, I want it out. Why should I care if it got there in 5000 miles or 20,000 miles?
Define High iron....

DB
 

Bob_Fout

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whitedog said:
But if your FE PPM is so high that it gets flagged, why would you want to keep it in there?
Total Fe alone isn't a valid metric. Wear rate is the metric.

Say an oil sample has 60 ppm of Fe. That could be good or bad, depending on how long the oil has been in use. Has it been in use for 10K miles or 20K miles?

If 10K miles, that's 6 ppm Fe/1K, and is a fairly high wear rate. If 20K miles, that's 3 ppm Fe/1K, a pretty low wear rate.

Total Fe ppm is flagged based on the wear rate.
 

whitedog

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Let's look at some easier to work with numbers...

Parts per quart.

The the oil lab says that there is 1 PPQ in the oil in my TDI, then I have 4.5 parts.

If I have 1 PPQ in a Cummins, (Call it a 10 gallon capacity, 40 quarts) I have 40 parts in that oil.

How does dilution come into play here?
 

whitedog

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Drivbiwire said:
Define High iron....

DB
The point where the lab flags it. It's somewhere below 66 PPM for a broken in TDI engine.

(Bad numbers here, but I'm going to leave it. See next post.)
 
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whitedog

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My bad on that number, I screwed up, but there is a point where they flag it. At some point, it becomes too high. I have seen one sheet that showed 100 PPM as abnormal.
 

whitedog

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I can understand why the wear rate will tell you how your oil is performing, but the total PPM tells you what is happening.
 

Drivbiwire

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Total PPM just gives you a value which is a required part of the equation used to determine how the oil is "actually" performing.

The total amount of iron does not tell you any more than what is in the oil. Iron by itself is not harmful to the engine, As long as the amount of iron being produced measured using Fe/1K remains at low values.

DB
 

Drivbiwire

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Actual samples + Ferrography

34ppm Fe (2.26 Fe/1K) 15,000 miles


22ppm Fe (3.14 Fe/1K) 7,000 miles


As you can see, low Fe does not tell the whole story. Both samples had low Fe but one had lower Fe/1K generation... Which would you prefer to have in your engine, the one with higher or lower total Fe?

DB
 
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whitedog

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One oil could have fewer, but bigger particles. That would cause more damage. Without knowing the size of the particles, those pictures are meaningless.

Also it doesn't address what a low value is, just that size matters.
 

Drivbiwire

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Size is the result of poorer performing oil. Poorer is identified by higher Fe/1K wear rates.

DB
 

whitedog

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Drivbiwire said:
Size is the result of poorer performing oil. Poorer is identified by higher Fe/1K wear rates.

DB
Size is the result of genetics.

It's also the result of type of failure if we are talking about engines.
 

DeliveryValve

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For those that are using an extended OCI, when do you consider changing out the oil filter? I am not sure how far an oil filter can go without clogging?
 

TornadoRed

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DeliveryValve said:
For those that are using an extended OCI, when do you consider changing out the oil filter? I am not sure how far an oil filter can go without clogging?
What do you consider an extended oil change interval? If 10k miles is normal, then is 15k an extended OCI? 20k?

Oil filters do not clog. If there was something floating around in your oil that might clog the filter, then your engine is already due for replacement.

There may be some inferior oil filters that won't last 10k miles, but I think even a Fram ought to last that long. MANN, Mahle, Wix, NAPA Gold... these are all filters that will last 20k or 30k miles if you choose to go that long.

There are folks who change the filters in between regular oil changes. Basically this removes about one quart of the old oil and adds one quart of new oil. Worthless if the old oil was worn out and depleted, pointless if the old oil was still strong enough to do its job.

I keep it simple -- replace the oil and filter every 10k miles. Nice round number.
 

wjdell

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The biggest waste is filters

The big waste is filters - the dump is full of them not used to even 50% of their life span. the oil is at least recycled.

For comparison FE Iron per 1000 miles my last UOA of LL III and my baseline of S9000

Oil ----- FE –- Miles ---- ppm
LL III --– 17 --– 7000 ---- 2.48
S9000 -- 3 --- 1316 ---– 2.28
 
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stefan_b

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I will start this post by saying that I really admire DBW, both for his knowledge and his willingness to share.

I believe (and I believe I can prove) that while part of the below is correct, there are misinterpreted results that support an incorrect conclusion.

Here are the points that will be challenged below:

1. Wear Rate is not higher in the first 5000Km - as inferred below. It is actually the lowest. Also, the more an engine oil is used, the more wear to the PRECISE and expensive parts is generated.
2. More frequent OC benefits the engine
3. UOA's are not a good indicator of CRITICAL engine wear - in the places where it really matters
4. A *very* critical aspect is filtration. Size does matter, and in my opinion, the smaller particle sizes pose a threat.

Brace yourselves for a lengthy post.

Let's start:


Drivbiwire said:
STOP STOP STOP!
[...]
VW does NOT want oil change intervals of less than 10,000 miles due to how the oils function in the engine, shorter intervals INCREASE WEAR.
Don't argue with me about it, if you take the time to track wear rates during an oil change at 250 mile intervals you can plot the reduction and stabilization of the wear rates out beyond 25,000 miles!
I believe this is misinterpreted data. Yes, wear rates (as determined via UOA's and normalized in ppm/l and 1000Km show these numbers, BUT:

Filters are a very important consideration. First of all filters... well filter - thus retain - contaminants. Therefore what the UOA tells us is what is the equilibrium level for contaminants in the oil.

To make matters more complex, filtration efficiency varies by particle size and by number of passes. In the real world (multi-pass) the numbers could be like so for a paper-type media:
40 percent capture efficiency at 10 microns,
60 percent at 20 microns,
93 percent at 30 microns, and
97 percent at 40 microns

Let's simplify by assuming an overall 60% filtration efficiency.

Contaminant (wear particles, among others) are generated differently depending on conditions - oil quality, engine regime, temperature, break-in, etc. But let's simplify by assuming an overall constant wear generation rate - say 10ppm/l for each 1000 miles.

This means that for the first 1000 miles, there are hardly any wear particles in the new oil.

At the end of the first 1000 miles, we would have:
Initial contaminants = 0 (fresh oil)
Generated contaminants = 10ppm/l
Retained contaminants = 60% of 10ppm/l = 6ppm/l
Free contaminants (FC) = 4ppm/l
---------------------------
2000 miles FC = 5.60 ppm/l
3000 miles FC = 6.24 ppm/l
4000 miles FC = 6.49 ppm/l
5000 miles FC = 6.59 ppm/l

See how the numbers evened out? Just like DBW stated, basing your conclusion on the UOA numbers lead to incorrect results - the wear rate was constant, yet the UOA numbers were increasing. This is NOT A SIGN OF ACCELERATED WEAR. Wear is constant in our very simple model. The increase in numbers is due to the system reaching equilibrium. It ends up at the point where the filter can retain the same amount that gets generated.

This is why IMHO, the following are incorrect:
1. The filter plays a very important role in masking WEAR RATES, as such basing a wear rate on the UOA numbers is relatively incorrect. THERE is a relationship between the UOA wear rate numbers and the engine wear rate ONLY WHEN THE SYSTEM IS AT EQUILIBRIUM.

2. The more an oil is used, the more smaller contaminants it holds. I will explain later on why IMHO, this is the really problematic aspect.


Drivbiwire said:
Anybody that tells you that short oil drain intervals are good for your motor don't know what they are talking about!

DB
This is where the problem starts; Contaminants (and by this I only reffer to those hard enough to cause scoring) come in sizes:

Large size (40+ um) - these are harmless - they are usually too large to enter the small clearances in a modern engine, and are safe to be trapped once they get to the oil filter.

Medium size (5-20 um) - these used to be the main concern - filtration is not great at these sizes, and they can and will score bearings and shafts. Also will affect cylinder bore. However these are too large for modern injectors or Inj-Pump units.

Small size (1-5 um) - these used to be disregarded all together - they'd pose no threat to bearings as the oil film is thick enough to immerse them. But in a modern PD engine, these are small enough to penetrate the between the pump shaft and inj body, causing scoring. Filtration barely exists at these particle sizes.

To cap it all off, the more you use the oil, the more it is filtered, the more small particles it will hold (the large/medium ones get filtered).

I don't know about you, but I'd rather change a set of bearings than a set of injectors...

There are many aspects left uncovered, as oil ages and its properties are affected. I am not pushing towards a 3000Mi OCI, but I think that 7500mi is the most I'd be comfortable using an oil for.

The mathematical model I used is brutal in its simplicity. A more detailed study would evidently provide more accurate results. However, even this simple model proves the point quite well.

Thank you for taking the time to read this loooong post.
 

TornadoRed

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I am not an expert, but I think the usual methods of analyzing used oil only measure the smallest metal particles, and totally ignore the larger ones.

Perhaps someone can refresh our collective memories about the differences between spectrometry and particle counters.
 

TooSlick

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Spectrographic analysis measures the concentration of dissolved metallic ions, along with solid particles < 10 um (microns). The key to the accuracy of the technique is that the range of particles sizes is assumed to form a normal distribution, ie a classic "bell curve". The subset of the total wear metal concentration measured with oil analysis is therefore representative of the total # of wear taking place. Note that this bell curve is truncated for particles > 25 microns, since most of these are removed by a good FF oil filter.

The TDI is actually very easy on oil, due to the very low amount of fuel burned for a given number of miles. In addition, the introduction of 15 ppm sulfur fuel (down from 500 ppm), has greatly reduced acid buildup in the crankcase, so even a 6-7 TBN oil like the VW 507.00 spec easily lasts for >10,000 miles.
 

stefan_b

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We switched to USLD quite a few years ago - still, where I live (Romania) we are not allowed to use flex service intervals due to dust content.

I believe that dust will affect the oil quite a bit, so we are still classifying all engines as going through "severe" conditions and changing the oil at least 2x as often as say Germany. This can easily be seen by comparing air filters - in Germany an air filter is good for 90.000Km (60.000 Mi) while we change them every 15-30.000Km. This is another factor to consider when determining OCI.
 

n1das

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stefan_b said:
Filters are a very important consideration. First of all filters... well filter - thus retain - contaminants. Therefore what the UOA tells us is what is the equilibrium level for contaminants in the oil.

[...]

To cap it all off, the more you use the oil, the more it is filtered, the more small particles it will hold (the large/medium ones get filtered).
Has anybody analyzed the contents in a used oil filter to determine exactly what was caught by the filter? Maybe we need to create a Used Oil Filter Analysis (UOFA) database.

After close to 400k miles :eek: of TDI driving (318k on my 02 Golf and still going strong, 73k on my 05 PD JWagen) :cool: and having ZERO oil-related issues with both TDIs, I'm completely comfortable with a 10k mile minimum OCI. It's a convenient interval, even with my driving ~ 1k miles/week. If bad weather or something comes up that forces me to delay a scheduled oil change until 11k, 12k, 13k, etc., even 15k if I have to, it's no big deal. I'll change it at the next convenient opportunity. I'm comfortable with my drive/worry ratio.
 
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Tom-R2

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I am not an engine or oil engineer. I am a driver/owner. I have 3 degrees, but they are all in the social sciences, not mechanical. I have little choice but to listen to the mechanical engineers who I have assumed worked these issues out through testing. From a reading standpoint, I really like DBW's detailed description. I don't think he dreamed that all up after a night of too many Coronas. He must have based it on something - probably from the company engineers. At least that is my (again) assumption. Since his explanation easily supports the manufacture claim of minimum 10,000 mile OCI, I am comfortable with that interval, and would not feel uncomfortable if I missed it a little, say to 12,500 miles. I'm at 9400+ miles with my '09 TDI and am preparing for the first oil change in a couple of weeks.

- Tom
 
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