Mobil AV-1 Under Attack

  • E-Mail this Article
  • View Printable Article
  • Text size:

    • A
    • A
    • A

A class-action lawsuit demands that thousands of TCM 470-, 520-, and 550-series engines that used Mobil AV-1 synthetic oil be grounded for tear-down inspection and overhaul at Mobil's expense. We urge owners not to panic.

Even though Mobil AV-1 has been off the market for nearly a year, concerns about engine damage attributable the synthetic oil continue to skyrocket. Hundreds of former AV-1 users have submitted damage claims to Mobil for premature cylinder wear, stuck rings, clogged prop hubs and governors, and various other powerplant maladies. Mobil has been quietly reimbursing claimants for repairs, and some owners have taken Mobil to court.

The latest wrinkle is a voluminous class-action lawsuit filed in April, 1995, which seeks to force Mobil to notify owners of the thousands of Teledyne Continental 520- and 550-series engines formerly operated on AV-1 oil that they should immediately ground their airplanes and submit their engines to a complete teardown inspection, and to require Mobil to pick up the tab for both inspection and repair.

This class-action suit is being brought by Malvern J. Gross, Jr., a 60-year-old retired partner of the Price-Waterhouse accounting firm who now lives in the San Juan Islands near Seattle. Gross is a 5,000-hour pilot, ex-president of the National Aeronautics Association, on the board of EAA, and has owned seven different airplanes since he started flying in 1955. Armed with the results of teardown inspections of two low-time AV-1 engines and the testimony of several world-class powerplant experts, Mal Gross appears determined to get the word out that AV-1 can ruin engines, cause catastrophic engine failures, and jeopardize life and limb.

Gross's suit is being handled by Lieff, Cabraser, Heimann & Bernstein of San Francisco, a law firm that specializes in large class-action cases and participated in the $4.25 billion silicone gel breast implant settlement, the $2.2 billion GM pickup truck settlement, and the $5.26 billion Exxon Valdez verdict. We'd guess Mobil is taking the suit seriously.

Unlike most of the owners suing Mobil, Gross doesn't appear to be doing this for the money, but because he passionately believes that his fellow aircraft owners must be warned of the grave danger of continuing to fly behind an engine that may have been contaminated by AV-1 use. On the day Gross filed his class-action suit, his lawyers sent a three-page press release plus the full 37-page complaint to the editors of numerous aviation publications.

While we commend Gross for his good intentions and believe he has an important story to tell, we're concerned that language of his lawsuit will panic a lot of owners unnecessarily. AV-1 oil had serious problems and undoubtedly damaged some engines. But we don't expect AV-1 engines to start falling from the sky without warning, as the lawsuit might suggest.

Mal Gross's Experience

N210MG is a Cessna T210L that Gross purchased new in 1975. He's put 2,900 hours on the plane since then. In November 1991, Gross brought his airplane to Victor Aviation in Palo Alto, California, to have its Continental TSIO-520-R engine majored. Victor overhauled the engine to new limits, and Gross picked up the airplane in January 1992. After 30 hours, he drained the break-in oil and started using Mobil AV-1. He continued to use AV-1 until mid-1994, changing oil and filter every 50 hours.

During this period, a series of compression checks revealed a deteriorating trend of leakage past the rings. In September 1993, a mechanic removed the prop from Gross's T210 and found significant sludge accumulation in the forward hollow portion of the crankshaft, which he cleaned out.

When Mobil announced that they were withdrawing AV-1 from the market in June 1994, Gross immediately switched to AeroShell W100 and hoped his compression would start to improve. But checks in October 1994 and January 1995 showed further deterioration, with compression readings in the low-to-mid 60s.

Gross decided to take the plane back to Victor Aviation for borescope inspection in January 1995. The engine now had 590 hours SMOH. The borescope revealed signs of ring damage and excessive blow-by. Victor pulled the #5 jug and found the cylinder wall scored and the oil control ring badly stuck as a result of sludge accumulation. They also pulled the prop and discovered a golfball-sized accumulation of sludge in the crankshaft. At this point, Victor recommended removal and inspection of all six cylinders, and Gross approved.

Gross also hired his own independent engineering consultant, Dr. Michael Wood of Aircraft Engine Failure Investigation, Inc., and a member of the well-respected aviation department of San Jose State University.

When Victor removed and inspected all six cylinders and looked inside the crankcase, they were so alarmed by the extensive sludge deposits that they advised a complete engine teardown to determine the condition of the crankshaft and bearings. Dr. Wood concurred with this recommendation, and Gross agreed to have it done.

The teardown revealed main bearings that were worn, crazed, and heat-distressed. Some showed evidence of shifting, and one bearing tang had scored the crankcase supports enough to require the case to be sent out for repair. The oil transfer collar was scored. The lifter faces were pitted. All of this was evidence of lubrication failure, and of an engine that might have failed catastrophically if it had been operated much longer.

Thick syrupy black sludge was. found coating the insides of the crankcase, oil cooler adapter plate, crankshaft, and crankcase oil galleys. John Pava of Victor believes this sludge contamination explains the lubrication failure that damaged the bearings and transfer collar. Dr. Wood told Gross that he was "a very lucky man" for having had the engine torn down when he did.

Ronnie Eriksson's Story

Meantime, half a world away, a Swedish industrialist named Ronnie Eriksson was also having problems with the engine in his. 1988 Beech B36-TC Bonanza. Eriksson is a 1,700-hour pilot and flies his Bonanza all over Europe on business. Its Continental TSIO-520-UB engine was run exclusively on Mobil AV-1 oil after the factory break-in oil was drained.

Like Gross, Eriksson was concerned about a deteriorating trend of compression readings, and about the accumulation of lead sludge found when the propeller was removed during routine maintenance. Eriksson was also plagued by high CHT and oil temperatures, for which he compensated by running the engine extra-rich.

In February 1995, with 633 hours total time on the airplane, Eriksson had his engine crated and shipped to Victor Aviation for inspection and repair. After receiving and inspecting engine, Victor informed Eriksson that he was probably looking at a complete teardown and major overhaul which would ground his Bonanza for months. Eriksson jumped on an airliner and flew to California to assess the situation personally. He brought with him his own engineering consultant, Ulf Dahlquist, who had been Chief Inspector for the Swedish equivalent of the FAA. So Eriksson, Dahlquist, Wood, and Pava all wound up inspecting Eriksson's torn-down engine.

Dr. Wood characterized the innards of Eriksson's engine as the blackest and filthiest he had ever seen in his career. The case halves, oil pan, suction screen, crankshaft bore, oil pump, and piston domes all had extreme buildups of heavy black syrupy sludge similar to that seen in Gross's engine but worse. The oil control rings were stuck, the main and rod bearings showed indications of lubrication distress. Dahlquist and Pava both reported severe cam lobe wear and spalling, and at least one main thrust bearing worn completely through to the shell. All three experts agreed that the engine would have been at risk of catastrophic in-flight failure had it been continued in service.

Because Eriksson is not a U.S. citizen, he is not formally a plaintiff in the Gross v. Mobil lawsuit. But his engine and testimony figure prominently in the documents filed with the court.

A Long Time Coming

Mobil introduced its 100% synthetic AV-1 piston aircraft engine oil with great ballyhoo in connection with the 1986 round-the-world Voyager flight. It went on the market in 1987, after five years of R&D and 25,000 hours of flight testing in 23 different aircraft.. Teledyne Continental enthusiastically approved AV-1 for use in all TCM engines with oil filters. It didn't take long before isolated cases of lead sludge accumulation became apparent in some (but certainly not all) engines using AV-1. Both John Frank of the Cessna Pilots Association and yours truly started advising against the use of AV-1 in low-utilization owner-flown airplanes as early as 1991. Our rationale was that 100% synthetic oil is a superb lubricant but a lousy cleanser, and that cleansing is extremely important in piston aircraft engines because of their loose tolerances and the significant blow-by that can leak past the rings and contaminate the oil. But while we suggested owners not use AV-1, we honestly didn't anticipate that the lead sludging problem could reach the severity revealed by the Gross and Eriksson teardowns.

All the while, Mobil continued to promote AV-1 with an extremely aggressive advertising campaign that made grandiose claims for the product: "a cleaner engine with little or no sludge, a 200-hour oil change interval, up to 30% less oil consumption, 10-15F cooler CHTs, and up to 5% fuel savings." Many knowledgeable engine people considered some of these claims to be exaggerated commercial puffery, and most considered Mobil's suggested 200-hour oil change interval to be insane. But owners lined up to buy AV-1 at eight bucks a quart.

Then, in a move that caught most observers by surprise (and delighted us), Mobil announced in June 1994 that it had decided to withdraw AV-1 from the market and to repurchase all existing inventory stocks. Mobil's press releases characterized this move as a marketing decision.

At the same time, however, Mobil sent a letter to owners of TCM 520- and 550-series engines stating that Mobil had just learned "during the past month" that in those engines "under certain conditions, the lubricant is not dispersing lead from the fuel as well as had been predicted on the basis of original flight and factory tests." Since then, Mobil has been quietly processing and settling individual owner claims for AV-1 damage. (See "Mobil's Position.")Why did it take so long for these problems to show up? The reason appears to be that the most seriously affected engines were in owner-flown airplanes that flew only 100 or 150 hours a year. (See "Which Engines Are At Risk?") Ronnie Eriksson's Bonanza is a good case in point. Erikson started using AV-1 in 1988, not long after it went on the market. He experienced symptoms of severe wear at only 633 hours, but it took him nearly seven years to accumulate those hours.

What We Think About This

It's important to keep all this in perspective. During the eight years that AV-1 was on the market, thousands of owners used it and the vast majority had good luck and no mechanical problems. Some noted an abnormal accumulation of lead sludge when the engine was torn down at overhaul, but most didn't. Only a relative handful appear to have suffered accelerated wear. We are unaware of any case of in-flight engine failure as a result of AV-1 use.

Nevertheless, we do not doubt that the Gross and Eriksson engines were badly trashed and at serious risk of seizure had they continued to be flown. And we do not dispute the suggestion that perhaps dozens or hundreds of other engines might be in the same boat.

The point is, however, that engines will almost surely exhibit clear warning signs of impending trouble long before internal damage becomes severe enough to cause in-flight engine stoppage. This was demonstrably true of both the Gross and Eriksson engines, and of several other engines we've followed that had to be overhauled prematurely after using AV-1.

The contaminated engines all exhibited deteriorating compression within 200-400 hours after starting AV-1 usage. Cylinder removal consistently revealed abnormal top-end wear, stuck and sludge-fouled oil control rings, and a thick coating of black sludge on the underside of pistons and on visible portions of the crankcase interior. Prop removal revealed a heavy accumulation of sludge in the hollow portion of the crankshaft and in the prop hub, and after the sludge was flushed out, it often redeveloped within 100 hours.

Consequently, it should be relatively easy for maintenance-aware owners of AV-1 engines to determine whether or not they are at risk. The great majority of them will not be. The notion that all AV-1 engines should be torn down as a precautionary measure seems to us like a colossal over-reaction.

We certainly don't want to sound like apologists for Mobil. It is inconceivable that they weren't well aware of the lead scavenging problems of AV-1 years before they withdrew it from the market. Mobil's own pipeline-patrol airplanes reportedly stopped using AV-1 because it gummed up their engines. Mobil engineers surely knew that Mobil marketing people were overstating the benefits of the product. We think Mobil should have yanked AV-1 a lot sooner than they did. Mobil should have come clean about AV-1's shortcomings and publicly announced their damage compensation policy, rather than quietly dealing with disgruntled owners on a case-by-case basis.

Mobil deserves to have their hands slapped over the AV-1 affair. But neither Mobil nor owners should be required to tear down or replace an engine unless clear evidence exists that the particular engine is at risk.

Specific Recommendations

If you used AV-1 in your engine for 100 hours or more (whether or not you're still using it or not), you should check compression regularly (we suggest every 50 hours when you change oil) and be alert for signs of deterioration. If you observe this, particularly in a turbocharged engine, you might be well advised to investigate further for signs of abnormal lead sludge deposits. The easiest way to accomplish this is to pull the prop and look for sludge accumulations in the hub and crankshaft. If those areas appear clean, you're probably home free.

If the crank and prop appear to be fouled with black sludge, you might borescope your cylinders or perhaps even pull off a jug or two and inspect for abnormal cylinder wear and sludge-fouled pistons and oil-control rings. While the cylinder is off, you can inspect the inside of the crankcase for black deposits, and inspect the cam lobes for evidence of lubrication failure.

Another danger sign in an AV-1 engine is any abnormality in propeller operation. Both Gross and Eriksson engines had badly scored transfer collars, and one owner we spoke to discovered that his engine was lead-fouled only after discovering that he could not control prop RPM.

Only if clear evidence of serious contamination is found would we consider doing a precautionary engine teardown inspection.

Status of the Lawsuit

Gross et al. v. Mobil Corporation et al. was filed in early April, 1995, in Federal District Court in San Francisco. With lightening speed (by judicial standards), the Court certified the class-action suit as a mandatory ("non-opt-out") class. According to our legal eagles, what this means is that all U.S. owners of TCM 520 and 550 series engines that used Mobil AV-1 are automatically parties to the lawsuit, and furthermore the class action probably will be their only legal remedy against Mobil. While denying the claims of the plaintiffs, Mobil did not argue against the Court's certification of the class...probably because it protects Mobil against having to defend hundreds or thousands of individual legal actions.

The Court also granted the plaintiffs' request for an order requiring Mobil to send letters to every TCM 520 and 550 owner of record, notifying them of the lawsuit and the plaintiffs' claims, and instructing them how to contact the plaintiffs' law firm for more information. (You can contact Lieff, Cabraser, Heimann & Bernstein by telephone toll-free at 1-800-956-1009, by FAX at 1-415-956-1008, or by email at

In September, 1995, the Court granted a plaintiffs' motion to expand the class to include owners of TCM 470 series engines as well. Once again, Mobil stipulated to the motion without a fight. The Court also set a tentative trial date in November, 1995.

AVweb will continue to follow this situation closely and report any further significant information as we receive it. Readers with AV-1 experiences to report are encouraged to contact us by email at

Mobil's Position

When TCM 520- and 550- owners were notified in June 1994 that it was pulling AV-1 from the market, Mobil's letter included an 800-number for owners to call if they believed they had "an oil-related mechanical problem directly attributable to your use of AV-1."Mobil is now dealing with at least 250 acknowledged owner claims of AV-1 engine damage, and we suspect the number is likely a good deal higher. At first, calls to the 800-number were being handled by John Esser and Frank Feinberg of Mobil's marketing company, Mobil International Aviation and Marine Sales, Inc. Later, claimants were referred to R. C. Gronwaldt in Mobil Corporation Claims.

Owners who called Mobil were sent a claim form and asked to submit photocopies of logbook pages, maintenance invoices, photographs, and other proof of the legitimacy of their claim. Some were asked to send Mobil pistons or other parts for inspection.

Most bona-fide claimants were quietly and politely offered reimbursement for a top overhaul, pro-rated to TBO. Many owners accepted this offer. Some who made a fuss were offered reimbursement for major overhaul or a factory reman (again, pro-rated to TBO) plus prop and governor overhaul and engine R&R labor. Mobil has consistently refused to compensate claimants for aircraft downtime, nor for engine mount or hose replacement or turbocharger and controller overhaul.

One owner we talked to has had his aircraft down for more than six months. Mobil offered to settle with him for nearly $18,000 covering a $26,000 factory reman pro-rated to TBO plus prop, governor, and R&R. This owner, whose airplane is extremely critical to his business, refused Mobil's offer and is suing.

To date, Mobil's handling of AV-1 claims has been strictly on a "squeaky-wheel" basis. Mobil has not notified owners that AV-1 might have damaged their engine, nor publicized the fact that Mobil is offering some reimbursement for engine repairs and replacement.

To claimants, Mobil admits that they are aware of cylinder damage, stuck rings, and contaminated propellers and governors resulting from inadequate lead scavenging by AV-1 oil. But Mobil apparently insists to this day that they know of no case in which bottom-end damage was directly attributable to AV-1, and dismiss as "impossible" the idea that AV-1 users might face increased risk of in-flight engine failure.

Mobil also contends that top-end damage attributable to AV-1 is strictly to confined to TCM 520- and 550-series engines, and has so far has refused (we're told) to accept claims from owners who used AV-1 in 360s and 470s or in any Lycoming engine. We are at a loss to explain how Mobil rationalizes this position.

While most of the owners we talked to had elected to accept the settlement offered by Mobil, a few did not feel they were being treated fairly and are going to court in hopes of obtaining what they considered to be full and fair compensation. We have no way of knowing at this point just how many owners are suing Mobil over AV-1, but the number of lawsuits is probably significant.

Which Engines Are At Risk?

Why were some engines so severely contaminated by AV-1 while most remained clean and healthy? Nobody really knows the answer yet. But we can make some educated guesses.

It's important to understand the mechanism at work here. Synthetic oil like AV-1 is composed of long, smooth polymer molecules that don't have all the little side branches that petroleum polymers do. This makes them extremely slippery and gives them excellent lubricating properties. Synthetic oils also lack the "light ends" of petroleum oils that can break down under extreme heat and create varnish and carbon deposits.

But it's those same smooth, ultra-slippery molecules that give synthetic oil its Achilles' heel: the inability to hold lead salts and other contaminants in suspension. The synthetic oil molecules are simply too damned slippery to hang onto such contaminants, so they settle out of solution and form sludge deposits, particularly in areas of oil stagnation such as prop hubs, oil pans, and the inside of pistons.

Tetraethyl lead is an octane enhancer used in avgas. It doesn't belong in the oil. Two compression rings on each piston seal the combustion chamber and keep combustion confined to where they belong. As long as the rings do their job well, the lead will go out the exhaust pipe and the oil will stay relatively lead-free.

But if combustion byproducts leak past the compression rings, a vicious cycle can begin. The third piston ring is the oil control ring, a spring-loaded slotted ring that receives oil from tiny feed holes in the piston and is responsible for spreading an oil film on the cylinder walls. If exhaust blows by the compression rings and fouls the oil control ring, its ability to lubricate the cylinder walls is compromised. Lack of lubrication results in accelerated wear of the cylinder and rings, further reducing compression and creating more blow-by. Within a few hundred hours, the compression may be down to the low 60s and the engine may be filthy with gooey black sludge. Some blow-by is inevitable, and engine oil is supposed to hold a reasonable amount of contamination in suspension so it may be drained out at the next oil change. Unfortunately, AV-1 didn't do this as well as petroleum-base oils.

We believe that AV-1 engines that exhibit good compression test results are probably not at much risk of sludge formation and sludge-induced lubrication problems. Engines that exhibit early deterioration of compression are at greatest risk.

Turbocharged engines appear to be much more likely to be contaminated because their higher combustion chamber pressures make blow-by more of a problem. The Gross and Eriksson engines were both turbo'd, and every owner we talked to in researching this article turned out to have a turbocharged engine. Ironically, AV-1 was especially popular among owners of turbos because of its resistance to coking under high heat.

It looks to us as if low-utilization engines (typical of most owner-flown aircraft) are more likely to be contaminated than ones that fly every day (such as Part 135 operators). The oil film on cylinder walls tends to strip away during periods of disuse, resulting in cylinder wall corrosion and metal-to-metal scuffing at the next engine start. Hence, low-utilization engines tend to wear cylinders faster.

At oil-change time, the sump should be drained immediately after flight while the oil is still hot and agitated. Otherwise, contaminants have time to settle out of suspension and form sludge deposits. This is good practice for all kinds of oil, but was especially crucial with AV-1.

The use of extended oil change intervals (as touted by Mobil's advertising) would have made the problem much worse. We spoke with a few owners who changed their AV-1 at 100-hour intervals, although most changed every 50 hours.

Finally, proper leaning is very important. Rich mixtures greatly aggravate the lead sludging problem because the fuel is not completely burned and the exhaust gas is loaded with lead and other unburned byproducts. This was clearly a contributing factor for Eriksson.