auto oil in aircraft engine

[6 Gun]

ok i know i will get flamed on this but i want some comments on this i purchased a case of 100w and the prices was over $54
so my ?
is anyone out there running a heavy weight auto oil in there Lyco its about 3 times cheaper
i know there is additives that are not in 100w but the base should be close
its not all that long ago that auto fuel had lead also
id like to here from any car oil users
bob

[flytoboat]

I'm no expert, but there are different formulations for different types of engines, i.e. air cooled vs oil cooled, high RPM vs low RPM, internal tolerances etc. How much does a new lyclone cost and how much does it cost to overhaul and compare that to your savings on a few quarts of oil over the life of an engine? Have you ever heard of the old saying "Penny wise and pound foolish"? Just my dos centavos.

[Sid Lambert]

I know people who have run car oil for years and many hundreds of hours with no problems but I would not do it. Car oil is designed to stay clean and not carry the dirt around. Aviation oil is the opposite. Look into the term "ashless dispersant" for a little more on this.

[RV6_flyer]

I use what the designer / manufacturer recommends in all my engines. The designer of the engines know more than what I do about keeping the engine running and lubricated correctly.

IF I thought I knew more than the engine designer / manufacturer, I would still be concerned about using a non-Ashless Dispersant oil in my air-cooled, high leaded fuel aircraft engine.

[aerhed]

Auto oils are pretty much all detergent oils. Aviation oils are AD(ashless dispersant. All that creamy gray lead paste (sludge) is supposed to settle into gobs inside your Lyc. and stay in fairly specific places. If you put detergent oil in an aircraft engine that has substantial time on it, it will break up sludge and move it around. This can actually clog oil passages leading to spun bearings, etc. I haven't seen much on operating a "clean" lyc on detergent oil, maybe not so bad. I know the rotox uses car oil but it's also not a "real" airplane motor.

[John Clark]

Modern automotive oils assume several important things including unleaded fuel, roller tappets (cam followers,) and the very tight clearances in modern liquid cooled auto engines. The presence of lead in the fuel changes the dispersant needs and the clearances change the viscosity needs. Saving a few bucks in either application is, in my view, foolish. 50 weight ashless dispersant in my Lycoming, 5W30 synthetic in my turbocharged Audi, by the book.

John Clark
RV8 N18U "Sunshine"
KSBA

[gereed75]

I am not that familiar with the detergent aspects of auto vs aircraft, but I am somewhat familair with issues regarding special addititives intended to help lube different types of bearings. The large "plain" bearings used in the lyco designs (especially at the cam and follower bearings) require different lubrication characteristics than the roller bearings and other types used extensively in modern auto engines.

This is a serious consideration for people running the old VW and Porsche designed engines and the builders of those older engines are very particular about what oils they run. There are some modern oils formulated with the special lube additives for these bearings - Brad Penn is one of them. A prominent builder of these engines (jake raby) has some in depth oil discussion on his site. Google "massive type 4" or "aircooled technology" to find Jake Raby's site.

Having said that, I wouldnt want to be the beta tester for any oil substitution program - what John said.

[noelf]

... there is a pdf in "The AeroShell Book" on "Piston Engine Oils". This information gives the why & why not to using the aviation oils in auto applications and vice versa.

[6 Gun]

thats good food for thought guys ive tried to study this for the last few years and iv read aeroshell and spoke with Ben at S-N-F lots of times but i want to get to the meat of the matter with someone that has ran modern oil and what results they have had
on another subject ive looked up data on MS sheets and some of the additives are mostly minerial spirits with a dab of acid that people pay 20 bucks a bottle for

[RVbySDI]

Originally Posted by Sig600

The post this was quoted from has been deleted

I think this is the crux of the majority of answers you are going to receive concerning your query. Experimental builders are building "Kitted", meticulously engineered, and mass manufactured experimental airplanes for various reasons and may be interested in some measure of experimentation. However, I would expect most are not willing to experiment on them to the point that their lives would be at high risk just to save money. It seems to me most replies are going to be along these lines and not on first hand experience.