No expert experience to offer here, but thought I would copy the two articles from Aviation Consumer Magazine for information. The first article is oil wear test (OCT 2002) and the second is oil vs corrosion tests (NOV 2002).
In our estimation, Shellís W100Plus and 15W50 demonstrate better anti-wear performance than the other oils. Understandably, Phillips X/C and Shellís W100 both failed our anti-wear tests when the testing pressures exceeded those typically found in GA engines. But these oils have no anti-wear additives so this wasnít especially surprising.
What was interesting was that Elite didnít do much better and it too failed, even though it contains what Exxon claims is a sophisticated anti-wear package.
Shellís W100Plus, 15W50 and Elite all meet Lycomingís AD80-0403 and contain a Lycoming approved anti-scuff additive similar to Lycís part LW 16702. However, in achieving this level of anti-wear performance, Shellís W100Plus and 15W50 oil may have a weakness in that their specific phosphate ester anti-wear additive is not hydrolytically stable. That means that it decomposes in the presence of water. The decomposition products are corrosive and tend to attack soft metals such as copper, lead and tin.
To some extent, this accounts for the copper leaching problem Shell has faced in years past with these oils and which has been reported in the field. Shell told us they have since added an additional copper passivator to combat this problem and weíve noted that field oil analysis supports Shellís claims.
Maintaining proper oil temps (above 210 degrees F) as well as frequent oil changes may minimize any corrosion problems that the phosphate ester anti-wear additive may introduce.
Even though Elite didnít fare well when compared to Shellís products in our lab wear testing, in the real world of infrequent oil changes and short flights, Elite may still be a good choice because it has impressive anti-corrosion characteristics, which we will be reporting on in a future issue. Further, it doesnít have the type of phosphate esters found in Shell, thus it has no moisture degradation problems.
So, which would we use in our engine? It depends. If the airplane is flown regularly on long flights and the oil was changed frequently, we would choose either Shell W100Plus or 15W50 semi-synthetic. It has the best anti-wear characteristics, possibly at the expense of some moisture sensitivity. But frequent oil changes can address that shortcoming.
If we only flew around the patch every month or two and only changed the oil every six months or so, then Elite would be an attractive choice, even though itís not as impressive as Shell from the anti-wear point of view.
AND CORROSION TEST RESULTS
Our tests showed that Shellís 15W50 and Elite were statistically equal in corrosion protection, even though Shell looks a bit better on the chart. Both did significantly better than Phillips X/C, which is a good representative mineral-type engine oil.
AeroShell W100 Plus, supposedly with the same anti-corrosion package as 15W50, didnít perform nearly as well as its semi-synthetic counterpart, a bit of a surprise we werenít able to explain. (Neither could Shell when we contacted them to ask.) To a degree, judging corrosion protection is subjective but itís also hard to miss which oils work well and which donít. This is done simply by judging what percentage of the panels appear corroded over what time frame. The benchmark we used for the chart above was 50 percent corrosion coverage. In other words, how long did the oil protect against that amount of corrosion?
The clear winners were Shellís 15W50 at 22 days followed closely by Elite at 21 days. At the low end of the spectrum was Phillips X/C at 16 days and Shellís W100Plus at 18 days. Off-the-shelf additives such as Avblend and Microlon didnít help, according to our tests. The Xtend super additive that Kollin tested (called variously ASL-2000 or GA2000 in the tests) drove anti-corrosion performance off the charts.
For all practical purposes, Elite and Shellís 20W50 finished in a dead heat. They both seem effective at corrosion prevention and the fact that AeroShell protected for a day longer is statistically insignificant. One thing we feel confident about, however, is discounting the notion that straight-weight oils protect better than multi-weights. The lab data doesnít bear this out. We think corrosion protection depends more on the additive package than the weight of the oil.
As noted in the accompanying article on page 7, Exxon has challenged our test results, both for anti-wear and anti-corrosion. First, letís examine the anti-corrosion issue. Exxon argues that our testing wasnít done in a lab environment and that hydrochloric acid isnít a combustion by-product.
We argue that engines donít exist in lab environments, they live on ramps and in hangars, exposed to wide variations in temperature and humidity. Further, the well-published Exxon tests, in our view, unrealistically use only humidity and the companyís graphs donít show a time scale.
As for hydrochloric acid, Exxon says that carbonic, nitrous, nitric, and sulfuric acids can be found in engine oil, yet they didnít use these acids in their testing. Our view is that Exxon relied on a test thatís a reference test, not one that correlates to aircraft in the field.
Our test was repeated with two different acid concentrations (.19 and .93 percent) and both gave the same directional results, with both semi-synthetic oils providing better protection than the unadditized oils. Further, hydrochloric acid, along with hydrobromic acid (from ethylene dichloride and ethylene dibromide lead scavengers used in leaded fuel) and acetic acid are used in the recently designed Ball Rust Test (BRT) for the American Petroleum Institute certification of passenger car oils. Passenger cars currently use unleaded gasoline and yet the API certification test still uses hydrochloric acid to increase the severity of the test.
On the anti-wear side, we take exception to Exxonís characterization of our tests as like ďTiger Woods playing bridge.Ē In our view and that of our expert, Ed Kollin, the tests are more akin to Bobby Riggs playing tennis. Exxon claims that the Falex pin test is normally used to evaluate heavy gear oils. Thatís true if the normal protocol is followed, but we reduced the pin pressures significantly to simulate more closely engine conditions, as we explained in great detail when we forwarded our results to Exxon. These pressures were dramatically lower than those used for standard extreme pressure (EP) lube tests.
Nor did we pull the test protocol out of thin air. We selected this test based on a paper published by Phillips, thus we believe itís a legitimate, fair test of anti-wear properties on an accelerated basis. In our view, the fact that Exxon Elite either failedótwice in our testsóor had higher wear rates in Exxonís own tests, suggests that its anti-wear package could be improved or is more suitable for an EP environment.
As we stated in the previous article in this series, any of the oils tested are suitable for use in aircraft engines. We canít honestly say that any of them are substandard or that any should be avoided.
However, we remain impressed with AeroShellís 15W50 multi-grade. It appears to us to be a good all-climate oil with excellent anti-wear properties and anti-corrosion properties. For anti-corrosion alone, Elite is essentially identical to AeroShell 15W50. If you prefer straight-weight oilsóand we canít make an argument for themóShellís W100Plus has good additives, too, although this oil didnít do as well on the anti-corrosion front.
Exxon did well in the anti-corrosion testing but, in our view, was far less impressive than AeroShell 15W50 in anti-wear protection. Weíre somewhat disappointed with Elite, in truth. We think Exxon had a good opportunity to deliver a new, high-tech oil with an advanced additive package but it appears to us as if it hasnít done that yet. (Are you listening Exxon R&D?)
Performance wise, Phillips X/C is an also ran, in our estimation. Itís not exceptional in either anti-wear or anti-corrosion properties, according to our tests, but our expert, Ed Kollin, says it has an exceptionally good basestock. Could additives improve it? We think so. But the right additives have to be used. In next monthís issue, weíll look at how some of the more common additives affect the performance of oils