Here are a few studies I mentioned previously:
I reviewed articles from the SAE conferences on powertrain and fluid systems in Tampa, Fl of October 2004 and the Paris 2000 conference. See SAE SP-1894 and SP-1550. Here are some excepts:
A New Method of Measuring Aeration and Deaeration of Fluids, Morgan et al:
Air in oil causes oxidation, wasted power, higher oil temperatures, loss of lubricity among other adverse effects. Higher RPM increases aeration, so does increasing oil viscosity. (‘Just FYI).
Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up).
Application of a Biodegradable Lubricant in Two Flexible Fuel Vehicles, Jesper Schramm:
Vegetable biodegradable oils were used showing good wear characteristics despite excessive thinning over time. (These may be next! Animal and plant oils have esters as in Red Line oils.)
The SMAC, Under Pressure Oil Aeration Measurement System in Running Engines, Bregent et al:
Oil aging, valve train and bearing problems and thermal problems occur with aeration. Below 110 C there is no problem but as one goes up the aeration ratio increases rapidly. (A cooler running engine from a thinner, faster flowing oil may lubricate better for this reason alone - aeration was a “hot” topic).
Development of the Sequence IV A Valve Train Wear Lubrication Test
art 1, Sagawa et al:
Viscosity data reveals that the more viscous oil did not significantly alter the cam angle of minimum oil film thickness. Of greater importance is the finding that the higher viscosity oil continued to exhibit boundary layer lubrication. (Ergo thicker is not necessarily better).
The effect of engine intake air humidity was significant so that tests are now done with specified humidity conditions.
It was postulated that fuel dilution of oil would elevate cam wear. Fuel dilution of 4.5 percent did not effect wear. (This would have the effect of lowering the viscosity about 1 grade).
The Effects of Crankcase Oil Viscosity on Engine Friction at Low Temperatures, Cockbill et al:
By using lower viscosity oils there is less friction, improved cold weather starting, improved fuel economy, a savings of starting system components and less wear by increasing the rate of oil pressurization and flow in the upper oil galleries.
Evaluation of Oil Performance Using the Tu High Temperature Engine Test With a View to Extending Oil Drain Intervals, Bouvier et al:
Oxidation and thickening is the limiting factor for oil longevity. Generally modern oils thin only 10 percent then thicken up to 60 percent within as little as 96 hrs. of operation ( -in the accelerated test engine. Let me comment that all test criteria are designed to mimic real engine operating conditions but at an accelerated rate).
There is accelerated acidification and corrosive wear that occurs.
Oil thickening was also time dependent. Thickening at 30,000 km was 2 times more when done over 21 months than over a 10 month period. (Change your oil every spring as I suggested before).
Development of the Sequence III G Engine Oil Certification Test, Clark et al:
Engine tests were made more severe again. (Over the years the oil ratings have improved but this has always been despite the increase in testing severity. It was III ...D, E, F, and is now III G). The oil inlet temperature was decreased from 155 to 150 C. The test was 80 and is now 100 hours. There were 8 oil level adjustments allowed now there are 5. The inlet engine air temperature was raised from 27 to 35 C. The engine load was increased 25 percent.
Despite all this the current 0W-20 oils were still GF-4 compliant and showed minimal wear characteristics as long as ZDP levels were higher than 0.03 percent. (The SM rated oils I have seen so far have levels of 0.08).
Other papers showed how they always consider older engines when formulating new oils for full backwards compatibility.
There was a lot on using thinner oils and how they do not result in excessive wear as previously feared. This is in part because of modern additives.
aehaas
