Component failure and UOA's....

[tdi-rick]

Had an interesting little lesson over the weekend.
A UOA was performed on one of our vehicles a month ago, as I was worried about fuel dilution with a mechanical fuel lift pump failure.
The fuel levels were fine, and most wear metals appeared near normal, excepting that the PQ index was up nearly double of previous figures. This didn't raise a flag at the lab, as they don't have an upper limit for the PQ index, only a maximum Fe level of 90PPM.
I put the increase in the PQ index down to the new plunger bedding in to the cam lobe, and the raised silicon as a result of Hylomar on the gasket.

Delvac 1 used throught.

Date 30/8/05 31/5/04 11/2/02
Km 168233 128084 121149
oil km 7000 17935 11000
oil add 0.6l 1.5l 1.5l

Al 4 11 7
Cu 2 7 3
Fe 16 34 19
Pb 5 7 5
Sn
Si 9 8 6
Fuel 1 1 1
Soot % 0.5 0.9 0.6

PQ Index 45 27 b>

Unfortunately I was wrong.

During a routine rocker check over the weekend, I found the valve stem cap on No 4 inlet valve disintegrated. All other caps are fine, all other valve/rocker clearances are fine, and haven't needed adjusting in over 60,000km.

Of course I'm replacing all the caps, but I'm not very enamoured with the thought of all that schrapnel through the system. I inspected the entrails of the OE oil filter, and the tell tale specks/chuncks of steel are there.

Anyway, just thought I'd pass on that a failure doesn't necessarily raise a flag at the lab.

 

[Doug Hillary]

Hi Rick,
I have posted this point on here many times

This has been my experience too - sudden failures or significant component "issues" are almost impossible to be picked up via UOAs. trending can highlight excessive wear (spikes noted too)

UOAs can be a valuable tool in diagnosing faults but one must be practiced and knowledgable of the engine family involved as well

Rest assured that the FF filters (and your centrifuge?) will have trapped the nasties

Thanks for posting
Doug

 

[Pablo]

Great post (and great point)

 

[bruce381]

Doug is right and I have said the same that UOA,s will show wear rates and a trend ONLY and that they will not all the time show impending catastraphic falures this is and still my argument against 5/20 PCMO's but thats another story. In this case perhaps a particle count or ferrography may or would have shown more value.

Bye the way what is PQ?? and what or how is it messured I do not know the term.
Thanks
bruce

 

[tdi-rick]

Thanks for the replies.
No Doug, this one doesn't have the centrifuge, and I didn't use the Donaldson Synteq filter (Beta 2=7) this oil change as the front diff juuust touched it under full articulation. It had an OE Land Rover filter in (made by Delphi, I think its @ Beta 2=25).
I've since 'modified' the diff housing so that the Donaldson is safe. Angle grinders are wonderful things.

Bruce, on my results sheet it says

quote:

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PQ Index - This test measures the Total iron in the sample, irrespective of particle size.

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[Terry]

rick, who is interpreting your data ? And is this a CAT lab ? What engine series ?

All the cutting edge UOA of any kind are worthless unless you have someone reading it correctly. You must have an analyst talking to you in a interactive collaborative fashion.

Most interpretations by the individual customer/owner and overworked lab techs remind me of a Dog watching TV, he sees movement but understands nothing.

 

[bruce381]

Understand PQ now do not know condeming limit but even if you have high wear, where do you look with so much steel rubbing on steel but I guess pulling a valve cover would have been a better option I like ferrograpy since you can see the photo of the "wear" particles that can give a better clue to what is wearing but I think test is high at $100 or so. still with new equipment or parts installed you would be right on having higher wear rates as the new component worn in so high PQ would not throw a flag.

bruce

 

[tdi-rick]

G'day Terry,

quote:

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..who is interpreting your data ?
And is this a CAT lab ? What engine series ?

All the cutting edge UOA of any kind are worthless unless you have someone reading it correctly. You must have an analyst talking to you in a interactive collaborative fashion.

Most interpretations by the individual customer/owner and overworked lab techs remind me of a Dog watching TV, he sees movement but understands nothing.

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I just receive the raw data from the lab, with a comment if anything looks 'out', so your last sentence is a valid point.

No, this isn't a CAT lab, it's through ALS(Australian Laboratory Services). They market their oil testing under several names, including a simplified service called 'e-monitor', 'Wear Check' for the heavy vehicle/machinery user, and have one or two labs in most states here. This, as with the three previous tests on this vehicle were performed through their Brisbane lab.

This isn't a large diesel, it's a Land Rover 300Tdi, which is a small displacement (2.5 litre) reasonably boosted (15.5 psi) direct injected diesel in a big, heavy crew cab four wheel drive that is worked hard.

 

[Doug Hillary]

Hi,
Rick - The ExxonMobil and Castrol Labs here use their field Engineers as "second level" UOA interpreters. The Lab technicians simply go by the programmed limits (they are set via their Enginners and the engine makers Engineers)and score the UOA accordingly

I never take the Lab's comments as absolute and within hours of my e-mailed UOA results a "collaborative discussion" is initiated via the respective Engineer. Over the years it would be fair to say we have learned about an equal share from each other. These fellows are now generally very practiced and aware of the end user's fleet mix and their common engine family's idiosyncracies

In time of course one's own database is the best source as engines within a family can vary so much

I stand by my previous comments

Doug

 

[1sttruck]

The PQ index is interesting, as it potenially adds a lot to the typical UOA by measuring 'all iron'. An additional question though, is it supposed to include the Fe from the wear metal count ? It doesn't seem to as it's lower than the wear metal, except for the last data point. I guess it also can't include whatever is in the oil filter, which I guess is why disecting an oil filter seems to be recommended practice on some aircraft.

 

[Doug Hillary]

Hi,
1sttruck - yes the PQ Index is an interesting adjunct to a UOA. The ExxonMobil Lab here in OZ has used it for many years

The PQ Index (PQI) is another interpretive component in our UOAs

If the PQI is lower than consistent Iron(example) in ppm then it is generally accepted that particles over 5 micron are not present
A rise in the PQI and a consistent or lowering of the Iron ppm number suggests that larger items are being circulated
The problem with many component failures is that initially the "big bits" either fall into the sump, are stopped by the intake screen or are picked up by the filter(s)

Even with warranty driven cam failures - a PQI of 16 (normally 1) and iron at 138ppm (limit 150ppm) did not enable us to determine that it was a cam lobe issue. 50k kms later the PQI had dropped to 7 and the iron risen to 221ppm but the silicon had risen to 63ppm. These engines have ceramic roller followers. It was the iron and silicon spikes combined with a slight audible miss at idle that enabled the correct diagnosis. The second and similar cam lobe failure after a further 18k kms was not picked up by oil analysis (in a UOA after 10k kms) but again by the distinct miss at idle

UOAs were of some assistance in the first instance but inconclusive in reality and note that the PQI actually dropped over time

Of course the engine did not suffer because of these higher than average readings

All part of the mystery of diagnosis

Doug

 

[Terry]

G'day Rick, Thanks for the response. Doug and tdi-rick, Please consider using our services in the future, you would be pleased I think!

I have many analysis customers in the pacific who would agree. Not many in Australia yet.

Doug is correct you must have background in BOTH the lab process, access to or experience with specific engine data ,metallurgy reference values and very helpful to understand how specific chemsitries work in a given design, weighted for ambient influences.
Is this the same engine that is used in LR in Europe ?

Collaboration is the key with someone that can accurately interpret the data.

I like the mystery part, intuition sharpened with emperical data is like a fighter pilot centerlining the opponent just right....Bullseye! Yeehaa...

 

[TexasTDI]

quote:

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Originally posted by Terry:
Most interpretations by the individual customer/owner and overworked lab techs remind me of a Dog watching TV, he sees movement but understands nothing.

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[Doug Hillary]

Hi Terry,
you said;
"I like the mystery part, intuition sharpened with emperical data is like a fighter pilot centerlining the opponent just right....Bullseye!"

Generally the diagnostic skills of modern mechanics has been offloaded to a computer!
While this can be fast and accurate a lack of basic skill often masks the correct result!

This has been occuring over the last several decades where the basic skills of diagnosing problems in motor vehicles (and other equipment)has been seriously compromised by poor training
In Australia and New Zealand a prime reason was a concentration on the "Academics" and a marginalising of the Trades. It is now being addressed in both Countries but the lead time is a decade or longer!

It really commenced with the introduction of EFI in the late 1960's. With heavy diesels the advent of ECMs stopped many fleets from undertaking any engine repairs at all!

We still find here that a good "bush" mechanic is better than most others. Finding them is difficult!

Doug

 

[XS650]

quote:

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Originally posted by Doug Hillary:
Hi Terry,
you said;

We still find here that a good "bush" mechanic is better than most others. Finding them is difficult!

Doug

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You run into some good mechanics in the third world. They have to be good to fix a variety of vehicles with nothing.