Doug Hillary

Hi,
used oil analysis (UOAs) has been used for many decades to measure lubricated wear metal (WM) uptake rates and the condition of the lubricant itself

CATERPILLAR made it an essential component of "critical equipment" management some four or more decades ago. By monitoring (trending) WM uptake against hours or distance they saved component failure and enabled the scheduled replacement of wearing components such as engine bearings, thrust bearings, chains gears and etc etc. Spikes (a sudden escalation) in any one or group of WMs can usually pinpoint an impending failure if detected and actioned quickly. Sudden failures of major components are beyond the realm of UOAs as we know them now. Internal coolant leaks are detectable

Used oil analysis is used extensively in many Industries today and is now a very reliable management "technology"

I believe 928 Auto owners can monitor their engine for such things as thrust bearing wear irregularities etc in a reliable way. It is just another diagnostic tool!

In the case of thrust bearing wear, monitoring three WMs namely aluminium, copper and lead - may provide a timely alert from which it is possible to avoid serious damage to the crankcase and shaft

It would involve taking three or four oil samples per year and submitting them for a UOA
The cost? - around $100-150!

The "normal" wear metal uptake range in a 928 is as follows;

Aluminium 0.5 to 1.5ppm/mile
Copper 0.5 to 1.5ppm/mile
Lead 1 to 2ppm/mile

Key;
ppm/mile = parts per million/per mile

Trending would show the oil's uptake of WMs occur at a regular and consistent rate
A "spike" would see a sudden escalation of the uptake of one or more WM's way beyond normal (eg. copper could suddenly rise to 30ppm in a short time between UOAs)
This would call for some further analysis to determine the cause

I do it - and I have used this maintenance tool for four decades or so!

Regards

bigs

Doug, your oil analysis posts are fascinating and always highly informative.

Do you mean that the cost of 3-4 samples a year is $100-150 each, or all together?

And, what type of businesses do such analyses? i.e. where do I get them done?

And finally, I remember a previous thread you posted where you gave a recommendation for the best brands and weight of oil to use in the 928. Would you repeat your recommendations please?

Now, playing devil's advocate, wouldn't it be just as easy - or easier - to simply check and measure the flexplate/torque tube tolerance once a year - and adjust as needed - to keep an eye out for TBF? I mean, if your UOA shows a suspicious WM uptake rate, isn't that what you'd do to follow it up and check things out anyway? Why not just do that task once or twice a year right from the start instead of the UOA's? Seems like you'd save yourself some steps and expense.

Doug Hillary

Hi Bigs,
yes you are correct that an inspection is worthwhile and the UOAs would provide "comfort" that all is well in between. And as you suggest a "delinquent" UOA would prompt another inspection. The UOA being but another "tool"!

Blackstone is one reputable Lab in the US that does UOAs - there are many others such as CAT and the reputable "name" ones are the best! The cost is around $US20-30 per UOA I believe - I pay $A50 here in OZ. I now test twice annually, at the oil change point, and about six months afterwards

Porsche recommends a 5w-40 viscosity synthetic or semi-synthetic oil for normal use. An oil that is Approval listed by Porsche is better than one that is not - there are many. M1 5w-40 T&SUV (a "cousin" of Delvac 1 5w-40) is a good product that performs very well in our cars

Racing requires a bit more consideration regarding engine/gear oils!

Regards

Garth S

Doug,
IIRC, your prior posts indicate that starting with fresh oil in a good engine, the metals uptake by the oil was reasonably linear in ppm/mile ... until they plateaued: thereafter, all concentrations were relatively static - and this observation was/is the support for extending oil change intervals.
If this is the case, what would be a resonable milage under 'normal' 928 driving to achieve entry to this plateau?
Yes, the question may be as xxxx as asking how long do brakes last - but it came to mind when thinking that any 'spikes' caused by such events as TBFwould be so much more evident after the oil hit its normal saturation point ( of metals concentrations).

bigs

Hi Doug -

Thanks for your answers. I have another question - bear with my ignorance here:

Do the three metals you mentioned - aluminum, copper, and lead - specifically point to thrust bearing wear? If so, why? How would you know it wasn't, say, piston ring wear or cylinder gouging?

And, related question, are there other metal combinations that would specifically point toward some other type of abnormal engine wear? In other words, do certain wear metal combinations serve as a "fingerprint" for certain engine problems?

This type of diagnostic tool interests me. As a physician, it is very analogous to drawing blood and running lab tests to help arrive at a diagnosis.

Doug Hillary

Hi,
Garth - you are correct, wear metal uptake rates are reasonably linear. UOA reports only give the accumulative numbers at any point. An initial and minor increase in the uptake rate(s) is often noticed if a different oil is used (a change of brand or formulation) and after an oil change. This is usually minor and the "plateau" rate is reached quite early (around 2k) with some elements then remaining almost static, the actual ppm being accumulative of course until the oil is drained

"Spikes" are usually immediately evident - an increase in iron of say from 6ppm at 3k to 36ppm at 6k indicates an abnormality. If this was combined with a linear but high silicon reading (and the engine had not been disassembled/reassembled with silicon sealants being used) it could be assumed that there is a leak in the air intake system
IMHO an imminent TBF would immediately show up as a very high spike in one but most likely all of the related metals. This is the indicator for an immediate and deeper diagnosis

bigs - a quick answer to your question is yes! Why? - all engines use a metallurgical "mix" but some remain fairly constant across all Brands and "families". Piston ring wear will show as iron and chromium as will "cylinder gouging" (usually)

The "soft" metals such as copper, lead are used in combination with aluminium and tin in journal bearing construction. Aluminium (alloy) is of course part of the crankcase structure too

It certainly helps to know the engine's metallurgical structure and indeed some engines produce their own signature. GM's V8s typically show high copper uptake rates, some Detroit Diesels produced high silver levels (used in an engine component) and many engines using ceramic roller cam followers show high silicate levels

Certain wear metal combinations and some non wear metal components in the UOA can give an accurate "fingerprint" to the practiced interpreter. Such things as PQ Index, Total Acid Number (TAN), Nitration, Water, Fuel and etc are but part of this matrix
You are correct in drawing the analogy to a blood sample analysis as part of an accurate diagnosis!

I hope this helps
Regards