As far as the issue of used oil analysis, let me share my HD fleet trucking experience:
I use used oil analysis primarily for maintenance planning. That is, since I use an expensive Delvac 1 fill, it only makes economic sense for me to dramatically extend the OCI, say 3-4X. Once the TBN decays, it's time to change out.
You can use used oil analysis to establish trends, but it is USELESS to determine things like Ring Stick or a connecting rod about to fracture. I have seen motors with "good" used oil analysis that had rings stuck and even broken, along with heavy deposits.
Another good application for used oil analysis is to see how efficient your air filtration system is working. A minor problem, say a cracked intake duct, can be caught early before major engine damage occurs.
Yep, I have caught that one. A small crack in the duct where you couldn't see it. In that case, the used oil analysis saved the motor.
When HD diesel motors first had the nasty problem with Top Grove Fill, used oil analysis was completely useless to answer the WHY question. Or even the HOW question. You needed test motors that were run on experimental oils and torn down to determine effects.
You also needed specially instrumented test motors that finally told us how hot the oil film was in the Ring Land area, which was the true cause of Top Grove Fill. So HDEO could then be reformulated to resist breakdown in the Top Grove area.
I still find it suspicious that CAFE is only used in North America. True, some makers have developed specially-formulated oils for certain markets and certain motors.
As an example: VW developed their VW 506.x spec with Castrol and came up with Castrol LongLife II 0W-30. The oil is designed for up to 2 year / 50,000km OCI in some gasoline and LD diesel motors. VW also cautions you this oil MUST not be used in other VW motors not specifically approved.
We then have that wonderful EPA memo that us civillians were never meant to see. So they take the results of the 16 hour test, the results of the 96 hour test, and ADD THEM UP. Then they add an EXTRA 0.5%. So even an oil that does NOTHING will still "earn" a theoretical 0.5% and be stamped with the GF-3 / SL "Starburst." The EPA is a LOT more concerned about indoctrination than about true savings:
http://www.epa.gov/otaq/cert/dearmfr/ccd0112.pdf
Of course, due to "clean air" requirements the EPA also approved MTBE. Ooops, that was a mistake, now they're quietly getting rid of MTBE. Oh well, I'm sure MTBE in our drinking water was a "small" price to pay for "cleaner" air.
Ever notice if you live in a non-compliant area you have to run oxygenates that typically lower fuel economy 10-15%? How does burning MORE fuel lower emissions???
Notice how CAFE has had the opposite of the intended effect: rather than reducing our fuel consumption, the CAFE nonsense and tiered emissions (Ford Excursion is a "green" vehicle!)has given us a fleet of pickup trucks and giant SUV's. We keep burning MORE fuel.
If you want to save fuel, drive a small 1 litre 3 cylinder s*** box. Though I must admit there are decent tiny cars out there.
I don't automatically bash thin oils and indeed would consider using Mobil 1 0W-20 when it dips to -40 here. In those temps, the slight increase in operating temp wear will be more than offset by decreased cold-start wear.
Machinery Lubrication has had VERY good articles about long-term concerns:
http://www.machinerylubrication.com/article_detail.asp?articleid=518&relatedbookgroup=Maintenance
http://www.machinerylubrication.com/article_detail.asp?articleid=529&relatedbookgroup=Lubrication
Remember that on average all the magic fuel economy "gain" results from intended shear. If an oil is "shear stable" then it can't be "fuel saving!" That's why when you examine the Sequence VIB Fuel Economy test, the 96 hour test by itself shows no gain.
If you also examine how lame the API/SAE requirements are, the "Starburst" oil is allowed to thicken +275%, 25% is allowed to boil off, the test technician can add 6.5 litres of makeup oil (Why car makers claim 1 qt every 1,000 miles is "normal"), and you're allowed stuck rings.
Since we have this myth of the 3 month / 5,000km OCI, that would be where you get maximum "gain" from light oils that have intentional shear. Once the oil thickens in service, what have you gained?
That's why most folks have noticed the longer they leave an oil in service, the less oil they burn. The oil has thickened and become less volitile. So why not buy an oil intentionally with a higher-rated HTHS and more shear stable.
Or, to get maximum fuel economy "gain" why not get a cheap "Starburst" oil and change the oil once a week or every 500 miles? You would then have an oil with maximum shear and maximum fuel economy.
I would imagine that a large motor loafing along really would be unaffected by choice of viscosity, within reason of course. A 15W-50 or a 5W-20 would perform the same at +70 F ambient, light load, and 1,400 RPM.
BTW: despite all the rhetoric, nobody has offered a good explanation of why CAFE oils are only used in North America. The same exact motor from Toyota or Honda carries a FAR different viscosity recommendation outside of North America.
Why?
No, it's not the fuel. The Europeans lowered their sulfur levels a few years ago. We still have higher sulfer levels. Also MMT in Canada.
Indeed, most Toyota and Honda motors only recommend 5w30 (No mention of xW-20) below +10 C / +50 F. The Honda H22A1 and H22A2 should only use 5w30 below 0 C or +32 F.
Jerry
