When an engine tanks prematurely, the recriminations begin. Did the shop screw up the overhaul? Was it bad cylinders? Or could it have been the oil you used? Yeah, maybe thats it…if only youd used Exxon Elite instead of Aeroshell, you wouldnt be looking at a mid-time overhaul. This is the sort of fear, uncertainty and doubt that advertising is meant to mine. And the copywriters are good at it. Elite, for instance, is touted as offering a two-fold increase in rust protection over the nearest competitor. Aeroshells popular 15W50 “helps engines start faster and eliminates need for seasonal oil changes.” BP is marketing Castrols aviation oil and not just claiming its the best, but offering to prove it with lab tests showing Castrol Aviator passed rust and engine deposit trials while its competitors failed. Whats going on here? Are the oil companies lying or just stretching the truth? In our view, its more the latter than the former-the engine oil ads make claims that are demonstrably true, but they make no effort to place these claims in context. The oil companies are happy having you make buying decisions in their favor with little grasp of the larger picture of oil performance. The reality is that aircraft engine operation is so fraught with variables that bench testing of oils illuminates only a shred of what you need to know to make an informed choice. The real meat of the matter derives from meaningful and in-depth data on field performance and this is almost impossible to come by. So if bench testing is of such limited use, why do it, as we did-expensively-for this article? Bench tests do allow comparisons of oil under controlled conditions which cant be duplicated in the field. All lubricating oils are expected to meet certain core performance requirements with regard to chemical composition, lubricity, viscosity, pour points and so on. Bench tests are the starting place to see which oil does what best. Second, corrosion protection is an increasingly important aspect of aircraft engine performance because airplanes don’t fly as much as they once did. Measuring how we’ll an oil protects against rust is still an imprecise science, but the lab analog for rust protection is more reliable than the analog for anti-wear protection, in our view. For this article, we set out to examine BPs claims and place them in the context of the larger issue of oil selection. Further, we compared our current first-choice oil, Phillips XC additized with CamGuard, to see if there’s reason to switch. Contenders If there’s such a thing as a big three in engine aircraft oils, its Aeroshell 15W50, Phillips XC and Exxon Elite, more or less in that order by market share, although Exxon may have edged Phillips by now. Since about the mid-1990s, BP has marketed Castrols Aviator products in Europe and elsewhere, but only recently has it made a run at the U.S. market with promotional campaigns. There are fundamental differences in the way these four companies approach the engine oil market. Phillips makes a line of monograde and multi-grade oils all based on mineral basestock-it doesnt use any blended synthetics, nor does it additize the oils. XC is a relatively simple, non-additized multi-grade mineral oil. If your engine requires Lycoming additive (LYC LW16702), you have to add it to the sump on your own. Both Aeroshell 15W50 and Exxon Elite are blended synthetics, consisting of a mixture of mineral oil and polyalphaolefin. PAO basestock was developed during and after World War II as a means of improving mineral oil performance in the turbocharged radials of the day. PAO has good low temperature performance and resists oxidation, but it has poor solvent characteristics, so its less good at dissolving combustion byproducts, which is why PAO oils are mixed with mineral oil. Aeroshell and Exxon have sophisticated additive packages and both meet the requirements of Lycoming LW16702, an anti-scuff compound. While the big three offer both multi-grade and monograde oils-some with additive packages, some without-BP/Castrol has pursued a strategy of offering mainly monogrades in up to four weights-65,80,100 and 120. The product we tested was Castrols AD 100, which, like Phillips XC, is a pure mineral oil product but with a full additive package, including compliance with Lycoming LW16702. Although most owners don’t think about it, there are substantial differences in prices between these oils. At $4.40 per quart (discount), Phillips XC is the least expensive, followed by Castrol Aviator at $5.90, Exxon Elite at $6.50 and Aeroshell 15W50 at $6.95. High to low, thats nearly a 60 percent price difference which, presumably, owes to the additive package and the PAO blending. But is the price Delta worth it? Our analysis follows.
Testing
The charts on page 5 summarize the test results and the sidebar on page 8 explains how the tests work. We hired Petro-Lubricant Testing Laboratories in Lafayette, New Jersey, to perform the trials. The labs director, Joe Wintermute, suggested two standard tests: the four-ball wear test and the Falex pin and v-block test. Although oil can be subjected to wide variety of bench testing, we agreed that these tests would give us the best general snapshot of the oils.
In addition, we conducted our own anti-corrosion tests which are summarized below. While the wear and pressure tests might not be definitive, we think the corrosion trials were and were comfortable making our recommendations using this data.
Four oils were tested: Phillips XC additized with CamGuard, Exxon Elite, Aeroshell 15W50 and Castrols Aviator 100AD. Reviewing the test results with Petro-Lubricants Wintermute, we believe the test data shows that all of the oils perform similarly. Among the four, there was no slam dunk standout, nor was there any meaningful poor performer. In the four-ball test, Exxons Elite did slightly better, with an even coefficient of friction and the smallest wear scar of any of the