Originally Posted By: TheOilWizard
Thanks everyone for all of your responses.
Dnewton3, your point in regard to wear numbers and extended intervals is well taken.
However, are you able to address the later posts in that extended OCIs, while they do not increase wear numbers proportionally, can lead to sludge/varnish formation? I am genuinely interested in your view on this.
First, we must understand that UOAs, by themselves, are not the end-all-be-all answer for everything. But, since none of us want to do or pay for an engine tear-down every 10k miles to measure bearing clearances and cylinder wall wear, we're kind of stuck with either not knowing anything (blind OCIs with no info), or using UOAs. I choose to be informed, and use the information to my benefit. I combine the UOA data with industry information such as engine family trends for failures (if any), and back that up with physical observations (checking coolant levels, PCs, noises, visual observations, etc ...). A single UOA does not tell us a whole lot. But a slew of them (from macro data analysis), from a bunch of vehicles with high mileage, indicates we can make very solid conclusions based upon propensity of positive experiences. IOW - if 500 different engines all of the same family exhibit a favorable wear rate of Fe, and those vehicles range from new to very-high exposure, then it's likely to be a tale of successful fortune when your one engine posts the same data as all others.
This is about statistical analysis. It's done ALL the time in production of toothpaste, stereo speakers, tires, gun ammo, bolts, water purification, etc ... And large groups are done with macro data analysis. If a company produces a product in high volume, and that product succeeds well in the market with a great reputation for longevity, then understanding the performance parameters of that product can predict similar/same experiences for successive products of that ilk.
As to the topic of sludge and such, I'll remind everyone that the UOA will tell us how the oil is doing in terms of this as well. Blackstone will give you an "insolubles" count; it's essentially a combo of both soot and oxidation. Other services will separate out the soot and oxidation. But the point is that it's not like we're blind here. The inference some folks make is that while wear metals rates are low, it's possible that there is a dastardly build up of sludge going on in the engine. Well, if your soot/ox counts are low, I'd like to ask those folks where in the blazes they think that "build up of sludge" is coming from? If it does not exist in the oil UOA, then how in the heck can it exist on the surfaces of the engine? Let's look at a few potential conditions and analyze the effects:
High soot and high ox in the UOA counts - it's possible that this could be a result of one of two things:
1) the numbers are high because the add-pack is nearing its limit, and while still capable, the oil is nearing saturation in terms of it's ability to hold contamination in suspension, and running much further will cause the precipitation of solids onto surfaces. If you OCI soon, it will be OK, but if you run much further, sludge will begin to form.
2) the numbers are high because the add-pack has already been overwhelmed, and it's truly leaving deposits on surfaces. i.e. it's too late; sludge is forming.
Either one of these conditions has to have precursors. The UOA would likely show a high insoluble count, or a high soot/ox count. It's not sludge can happen and not show up in the lube. If you're getting sludge on the engine, and you're not paying attention to the UOAs, is that the oils fault or yours? It's up to you to manage the OCI, not the oil. The oil does a job. It's your job to track the oil's success. If your engine is sludged up, it's due to your negligence and not the lube's fault.
Low soot and low ox in the UOA counts - this can only be a result of one thing ...
The oil add pack is doing it's job. The contamination is being controlled by the additives, and the oil is no where near being overwhelmed.
My point is this ... We get good indication in the UOA as to whether sludge is going to form or not, because we can see if the lube is anywhere near being compromised. If the UOA counts show high soot/ox, then you'd better start looking physically for sludge by pulling off a valve cover, using a bore scope, etc. But if your insolubels are low, then there is very little chance that you're at risk for sludge. It is impossible for contamination to bypass the lube and travel from combustion right to the surface of the head or lands of the rings. It has to be carried places by the oil. So if your oil shows a low soot/ox contamination level, it's likely that sludge isn't forming. There are times when you'll see small pockets of heavy varnish in the corners of a cylinder head, because the oil will pool in a small pocket. While aesthetically distasteful, that's not going to cause an engine to seize up; this must be kept in context.
In short, the oil cannot deposit something on the engine surface that does not exist in the lube itself! So if your UOA looks good for soot/ox, then your engine is likely not being sludged up.
As for the comment from others about Al and Fe wear rates, clearly those are to be considered as well. However, I can say with absolute certainty that Fe is the number one cumulative metal in a UOA. Almost always, the other four (Al, Cr, Cu, Pb) will be in the single digits, regardless if you run 3k or 13k miles. I wholly agree that watching all wear metals is important, but those will typically fall to near or below 1ppm/1k miles; a wear rate so low as to be able to relieve all concern. I'm not saying to ignore them; just understand that they tend low and stay low, most of the time. A time to be concerned with the others is when you see them in context of other concerns. If you see sodium/potassium rise and also metals rise, you've got coolant intrusion. If you see both Fe and Cr rise, then you've got cylinder/ring wear. If you get Al with your Fe, it's piston wear. If you see Al alone and it's a Ford, it may be bearings. If you see first Cu and then Pb, it may also be bearings. All this has to be in context. But generally, a good wearing engine will ONLY show an accumulation of Fe with the OCI extension. The other metals tend to blip up at the front end of the OCI, and then settle down to very low levels after that.
Occasionally we'll see Cu spike alone; typically a reaction from a Cu based oil cooler and a chemistry change in the lube being used, such as one with high esters or amines. I cannot explain this phenomenon down to great detail; I'm not a chemist. But I see the evidence of it at times, and accept it for what it is; essentially harmless. Cu could also be a bearing, but would likely be followed by Pb shortly thereafter. If Cu spikes after a lube change, and then settles over successive OCIs, it's just the chelation of Cu from the reaction.