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Steve Bergin, a research engineer with General Motors, recently gave presentations to several technical groups, including Saturn Corp. field engineers. He addressed two "myths". According to Bergin, "Other than running out of oil, the primary oil-related problem that kills engines is DEPOSITS that cause stuck lifters, stuck piston rings and blocked oil passages. IT IS NOT WEAR". Secondly, "Engine oil viscosity has VIRTUALLY NO EFFECT ON WEAR."
Recent lower viscosity recommendations by the auto industry are based primarily upon the fact that new engines will start at much lower temperatures than previously, he said, and the oil must be pumpable.
Deposits and Wear
Bergin begins with an up-front caution: "Don't add anything to your oil." That's a message found in every owners manual.
Then comes his principal message. "If the oil protects the following components, everything else in the engine will almost certainly be OK."
First, the oil must fill and prevent sticking of the hydraulic valve lifters, Bergin explained. "Every time an engine is stopped, some cam lobe will be holding a valve open -- and over a period of about an hour the lifter plunger will be driven down low into its lifter body by the force of the valve spring. If the lifter plunger sticks in this position after the engine starts, because of rust or varnish, the valve cannot follow the full lobe profile, and slams closed. The entire purpose of the lobe profile is to decelerate the valve as it approaches its seat, so that the valve hits its seat gently.
"But if the valve hits its seat hard enough for a long enough time, the valve will break, and this will destroy the engine."
In addition to its sealing role, the oil must protect piston ring operations. "Pistons are always made of aluminum, get real hot and expand a lot. To avoid seizure when hot, cold pistons must be relatively loose in their bores. Piston rings, when wet with oil, provide the sealing that is necessary for compression and starting and must be free in their grooves and stay in contact with the cylinder wall.
"If rings stick when cold, starting is difficult. If rings stick when hot, oil consumption, oil degradation and blowby increase and deposits causing ring sticking are likely to get worse.
"Stuck rings can act like cutting tool inserts that scuff the cylinder walls -- which ultimately leads to piston seizure in the bore, and engine destruction," Bergin related.
Third, the oil's ZDDP (zinc dialkyldithiophosphate) additive is very important in protecting heavily loaded, boundary-lubricated parts, such as cam lobes, valve lifters, piston rings and cylinder bores. Boundary lubrication results when metal-to-metal contact occurs, "which in turn causes the deposition of the antiwear film from ZDDP."
While the antiwear properties of ZDDP will not completely eliminate wear, "they will reduce wear by orders of magnitude so that it will not likely be a limiting factor on engine life," Bergin said.
Phosphorus is an important component of ZDDP and, as well, a poison to emissions systems above certain levels. The auto industry has definite concerns about the use of phosphorus above a certain level, and considers phosphorus above 0.10 percent mass in a motor oil to be an emissions systems threat.
Bergin says, "New formulation technology can use ZDDP much more effectively. However, the oil viscosity will not have any practical effect on wear."
Indestructible Bearings?
The other major part of the engine that oil must lubricate and protect is journal bearings. Examples of journal bearings include the points where piston connecting rods join the crankshaft and where the crankshaft is supported in the engine block.
Bergin notes that with undamaged journal bearings, "If a journal bearing initially contains a film of oil, it is simply not possible to squeeze all the oil out by any loading of the bearing. If the bearing and journal are not damaged, the surfaces simply cannot be forced into contact. Undamaged journal bearings with debris-free oil flowing are virtually indestructible."
How strong are bearings? Bergin noted, "As part of our quality control operations, we conducted 'torture' tests in our laboratories where engines are run at top speed and load, and are deliberately supplied with inadequate cooling so that both the coolant and oil temperatures continue to rise until the engine fails.
"The failure mechanism at truly extreme temperatures is partial lifter collapse followed by valve breakage and piston destruction. The bearings, however, are not damaged in any way."
So how can indestructible journal bearings ever fail, aside from damage from debris? Bergin states, "Bearings get damaged and fail at a later point, even with the oil flowing, most often by oils that have too high a viscosity, and thus are not pumpable at the extremely low temperatures that today's engines will start."
That last sentence contains two key elements -- "today's engines" and "too high a viscosity."
The Low-Vis Myth
The auto industry is under protracted pressure from governmental units, "green" organizations and the public to reduce the amount of pollutants derived from their engines and to use nonrenewable resources to best advantage. Those pressures have resulted in continuously improved spark ignition engines, including electronic ignition and fuel injection as well as greatly improved starters and batteries. These engines produce much greater fuel economy and lessened air pollution -- and are also able to start at far lower temperatures.
Bergin points to a common belief that "the need to improve fuel economy has led auto manufacturers to recommend lower viscosity oils that cause more wear than higher viscosity oils." But all evidence, he says, indicates that viscosity has virtually no effect on wear.
"Recent lower viscosity recommendations are based primarily upon the fact that new engines start at much lower temperatures than just a few years ago. In fact, unlike earlier engines, starting is now almost independent of cranking speed and duration."
The need to improve fuel economy is another driver that has led auto manufacturers to move to lower viscosity oils, such as SAE 5W-30 and even 0W20 and 0W-30.
These lower viscosity oils that auto manufacturers recommend today (primarily SAE 5W-30 and 10W-30) do not cause increased wear, he reiterates. Using the oils recommended in owner's manuals (GF-2 currently, and GF-3 in possibly mid 2000) will insure that deposits will not form in critical areas. And bearings, too, will not be damaged or fail unless they lose oil supply long enough for the thin film of oil remaining in the bearing to get so hot that it decomposes.
"Journal bearing damage and failure are caused by the thermal overload that occurs when the oil supply is cut off. Mechanical overload does not cause journal bearing failure -- except in the isolated case where extreme mechanical thrust overload can cause attached flanges to fail, regardless of oil viscosity."
The Thickness Threat
Threats to engines come from a number of sources, including such obvious ones as using the wrong quality oil (SA or SB oils, for example, which contain no antiwear additives). Or not changing the oil at the proper intervals.
And Bergin notes that a threat to an engine today, including bearings, can come from another source. "Bearings get damaged most often by oils that have too high a viscosity and thus are not pumpable at the extremely low temperatures that today's engines will start at."
What constitutes "too high a viscosity?" Beyond noting that auto manufacturers have recently begun recommending lower viscosity oils, such as SAE 5W-30, Bergin made only one recommendation to Saturn engineers: "do not use SAE 20W-50 oil or any other viscosity grade that is not recommended," he stressed.
Bergin followed up with a qualification. "Viscosity is not an issue [in cases] where extremes of either temperature or high load service do not exist."
Overall, he feels, "There's lots of misunderstanding about oil viscosity, much of it from oil company messages which are intended to generate a marketing advantage."
There is certainly no conceivable threat regarding low-temperature viscosity in St. Thomas in the Caribbean. But there would be in the high ski areas of Colorado -- as well as above the 40th parallel of latitude, which cuts through Philadelphia on the east and just below Salt Lake City on the west.
Extreme fluctuations of weather seem to have been a fixture for a number of years -- and may not lessen in the future. Add this temperature fluctuation to the fact that current engines can start at extremely low temperatures and, following Bergin's points, it suggests the possibility for an oil-related incident to surface -- with higher viscosity grades being the culprit.
