Notes on Corvair flight engine oils.


A friend of ours sent in a question on oils, which was sparked by reading an internet discussion group story about “experimenting” with oils for Corvair flight engines. It is a free world and people can do as they wish, but to my perspective, the subject of oil for Corvair flight engines is very simple.

Below is a picture of Shell Rotella T 15W-40 oil. This is the oil that we suggest people use in their flight engines. I am going to guess that 90 percent of the hours logged on Corvairs last year were done with this oil. We have been using it since 1996, and I have had a very long time to examine the long-term wear characteristics, it’s ability to withstand heat, its compatibility with 100LL, and it anti corrosion characteristics. This oil is a winner on all fronts. Add to this, that it is available at any auto parts store or Wal-Mart and it is fairly cheap, and I begin to ask myself why anyone would be looking for another oil.

In the manual, I try to teach my saying, “It isn’t the probability of being right, it is the cost of being wrong.”  Oil example: Years ago, Woody Harris, our west coast guy thinks that Aeroshell is airplane oil, and may be better for our “Airplane” application. He is pretty sure this has good promise. Here was the cost of being wrong in that instance: His engine ate the new cam and lifters in 1 hour of running on Aeroshell. This is because the element we care about, Zinc Phosphate is about 800 PPM in Rotella, about 200 PPM in normal oil, and ZERO PPM in Aeroshell.

Let’s say you have always used imaginary Dyno-syn 10-40 in every car you have had in the last 10 years with great luck. It doesn’t count: Modern cars have roller cams, and don’t need zinc. Lets say you have used Unicorn 20w-50 in all your cars for the last 30 years, and all your cars were Corvairs. It doesn’t count: You didn’t run your cars on leaded fuel, and this matters. I could go on like this for a while, but you get the point. Any recommendation has to be just about what we do with Corvairs.

OK, what about synthetic? OK, why use it? “It has good heat resistance”. So does Rotella, which you can actually run at 300 F without hurting it. If your engine runs hotter than this, lack of synthetic isn’t your problem. OK, “I want to go 100 hours between oil changes and having to look in the cowl.” If this is a goal of yours,  walk over to your book shelf, take my manual down, put it in an envelope, write “I want a refund because I couldn’t learn anything from WW “ on the outside, and mail it back to me. Oil changes are a very good inspection point on aircraft engines, and a tremendous amount of small issues are caught and corrected before they become a problem.  Your engine is your personal masterpiece. You should be tempted to pull the cowl off and just marvel at it for no reason.  You should drag passers-by at the airport into your hangar and proudly say “LOOK! I built That!” With an arm gesture that magicians use as they say “TAA-DAA!”

25 hours is a reasonable goal on inspections. You could probably run 50 hours on Rotella between changes but learn this phrase that every A&P worth a damn has tattooed on heart: “Gas and oil are the cheapest things you ever put into an engine.” Here is the WW corollary: “Gas and oil are also the easiest ‘parts’ to install.”

 Lets say a real cheap sob likes to lean his engine beyond peak egt because he read an article written by some d-bag in Flying magazine, and this article sounded great because it provided techno-mumbo-jumbo, (complete with graphs!) that justified Mr cheapskates inner need to avoid spending a dime. At the end of the year, he gets out a calculator and finds out he had a 22% better time than other pilots because he “saved” $1,200 by leaning his engine and only changing the Kmart house brand oil once every 100 hours.  Problem: He does a differential compression test and finds out that he detonated his pistons to death and scoured his cylinder walls, You guessed it, he is out $1,200! net savings: ZERO.  But the big one: How much extra time did it take me to change the oil four more times and pump another 200 gallons of gas in my plane? Think that Mr. Cheapskate can overhaul his engine that fast?

Do you want to try some “super special, secret ingredient, made by Amish people who don’t use combustion  engines, purple/green/ yellow, Brad-Penn, Brad Pitt/Sean Penn oil?” Go back to question #1: What ‘problem’ are you ‘solving?’ Read my story about The Panther engine again. It just had a perfect break in run and test period, it has perfect compression, it doesn’t run hot, the oil doesn’t get consumed nor leak, and wait for it…..It was all purchased for $12 a gallon at the 24 hour super Wal-mart. And this is not good enough because???????

One last thought here: If a builder spend many hours talking about super special oils, and how they can fix everything in your life including your 401K, and spend a lot of time talking about this on the net and later comes to a college but has no idea how to install a distributor and set timing, I am going to tease him about spending a lot of time thinking about synthetic oil, an answer in search of a valid question,  when he needed to be reading about the fundamentals of his engine.

Do you want to try synthetic? Look at Amsoil 10w-30. We ran this for many years. It is great stuff. The reason why I trust it is that it has long been proven to work in airplane engines with 100LL. In the 1980s it was marked for general aviation aircraft. It has a track record of working. BTW, I have never seen a Corvair engine run any different pressure or temp with synthetic oil. Anyone who has was probably imagining it because they wanted to see it. The one thing that isn’t imaginary is synthetic oils ability to leak out of engines. If your engine leaks a little with mineral oil, try switching to synthetic, flying an hour and looking at the bottom of your plane. You will be temped to yell out “Jed’s a Millionaire!” (A&P mechanics do this when the spot a giant oil leak.)

Very Important: You should put additional ZDDP in the break in oil, and there is no harm in running it during the rest of the life of the engine. You can learn more about it at this link:

If you would like some more information on why ZDDP is important, read this link:

5 Replies to “Notes on Corvair flight engine oils.”

  1. My guess is you’ll never even see this comment that’s appended in 2016 to a 2013 post, but I don’t see anywhere else to put it. Maybe somebody will be doing a Google search one day and run across it.

    I’ve been meaning for a long time to ask, William, whether you have visited I found it pretty compelling. The guy seems to be qualified and appropriately motivated. His views on zinc additives certainly seem to go against the norm but then his test results seem to support his position.

    I’m no expert, but I thought you’d find interesting how he rated your favorite oil, Rotella T, which is the 140th best oil for wear protection on his list. You might want to try 5W30 Pennzoil High Mileage Vehicle, API SN, conventional oil, which is #34 on his list and also available at WalMart.

    1. Robert,
      I get an email for every comment that gets posted on this blog, even to older stories. I will gladly go and get an open minded look at the story you have shared. When I look at oil reports, I have to keep in mind that they are not directed at air cooled, flat lifter motors running on 100LL, and these factors have to be considered. Our use of ZDDP is a requirement from our cam grinder, and the one guy who debated this ate his cam in 4 hours, polluting the whole inside of his new motor. He was using aeroshell which has no ZDDP. It was not an assembly error, as they guy is an internationally known engine guy, and when the problem was corrected, he went on to fly 490 hours to date on his Corvair using Rotella.

    2. Robert,
      I just spent 30 minutes of my life looking at the link, and I will say it didn’t impress me. I will confess that I guy who goes on at length about all of his engineering experience, but of course, will not tell you his name, nor the name of where he works, not show a single picture of testing, isn’t going to get my attention for long. None of the testing is done in engines? I have had too many opinions from internet mystery name people over the years to believe they know a secret that people who have real names are too stupid to have found. -ww.

  2. In looking at availability for Shell Rotella T 15W-40, it appears to have been replaced by Shell Rotella T4 15W-40 (API CK-4). Curious if you consider this version of Rotella to be equally useful in a Corvair engine? Beyond that, it would be very useful to hear your thoughts on the fully synthetic version of that, Shell Rotella T6 15W-40 (API CK-4).

    1. the T4 works just the same. I suspect the T6 would also, but have not tested it. The engine would not care, the issue is fuel compatibility which needs to be evaluated. I have used Amsoil synthetic in Corvairs, but it was formulated to be compatible with 100LL fuel. This is not known about T6 yet.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.