For years, we've warned against the use of fully synthetic oil such as Mobil AV-1 in most owner-flown airplanes because of its inability to hold lead and other contaminants in suspension. We've also cautioned against the extended oil change intervals suggested in Mobil's promotional literature. Now TCM has removed AV-1 from its list of approved oils, and Mobil has withdrawn it from the market.
This article originally appeared in CESSNA PILOTS ASSOCIATION magazine and is reprinted here by permission.
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Mike Busch is editor-in-chief of
AVweb, a member of the technical staff at Cessna Pilots Association, and in a
prior lifetime was a contributing editor for The Aviation Consumer and IFR
Magazine. A 6,000-hour commercial pilot and CFI with airplane, instrument and
multiengine ratings, Mike has been flying for 36 years and an aircraft owner
for 33. For the past 14 of those years, he's owned and flown a Cessna T310R
turbocharged twin, which he maintains himself. In his never-ending quest to
become a true renaissance man of aviation, Mike's on the verge of earning his
A&P mechanic certificate. Mike and his wife Jan reside on the central
coast of California in a semi-rural area where he can't get DSL or cable
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In a press release on June 10th, Mobil announced that it had decided to permanently withdraw its AV-1
fully synthetic oil from the market, and was recalling existing stocks of AV-1 from its distributors.
In recent months, both Mobil and TCM became aware of a number of cases in which severe deposits of lead
sludge were discovered in big-bore Continental engines that had been operated on AV-1. As a result of these
reports, TCM decided to remove Mobil AV-1 from its list of approved oils. Mobil then decided to withdraw
the product from the market altogether.
So What Should I Do Now?
We recommend the following procedure when discontinuing the use of Mobil AV-1:
Fly the airplane for at least 15 minutes to bring the oil fully up to operating temperature and to agitate
any sludge into suspension. If you have a constant-speed propeller, deep-cycle the prop control several times
both before and after the flight in order to de-sludge the propeller hub.
Drain the oil as quickly as possible after the warm-up flight to insure that contaminants are drained from
the sump before they have time to settle out of suspension.
Change the oil filter or clean the oil screen.
Service the engine with a 100% petroleum-based AD oil such as Aeroshell W (single-weight) or Phillips
X/C (multi-weight). Petroleum-based oil has the greatest capacity for scavenging any lead deposits that may
have been left by the AV-1 and holding them in suspension.
Drain this oil after 10 to 20 hours of operation. It is likely to be dirtier than usual, having scavenged any
deposits left by the AV-1.
Change the oil filter or clean the oil screen.
Service the engine with whatever oil you intend to use on a regular basis. The CPA Tech Center generally
suggests using a single-grade petroleum oil such as Aeroshell W 100 for optimum protection against
corrosion. For cold weather operation, a multi-viscosity oil such as Aeroshell 15W-50 or Phillips X/C 20W-
50 may be used.
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In a press release on June 10th, Mobil announced that it had decided to permanently withdraw its AV-1
fully synthetic oil from the market, and was recalling existing stocks of AV-1 from its distributors.
