Adding oil to the fire

[raytoews]

Any "expert" knowledge out there to answer my questions?

I have a Viking/Honda engine in my Zenair which uses regular automotive $6 oil as specified by the manufacturer.

My Lycoming powered Grumman calls for $12 aviation oil.

For the life of me I have a problem seeing the difference. Well yeah,,,,,6 bucks x 8 liters = $48

Is the bearing clearance or seal composition different. Do they react differently at altitude. Do people in Denver use special oil? What oil do the air cooled VW derivative engines use? Or is it because WE HAVE ALWAYS DONE IT THAT WAY!

I understand oil viscosity in aviation oil is doubled, so a 30w auto oil is a 60w aviation?

As an aside,, I installed an Anti Splat oil separator and vapor extractor in my Grumman and last oil change I put in the full 8 liters.

At 60 hrs (overdue) I have added 1 liter and is now down to 7 liters!! This in an engine that used to be filled to the "normal" 6 liters and used a liter every 10 hrs??

As a second aside,,,I have a 2012 Lexus, I use synthetic oil, and change at 10k kilometers. We ran it over last change by a few thousand and the mileage went from 24mpg to 18. We stop at Mr Lube and the mileage immediately went back to 24mpg. The dash display indicated and confirmed (incredulously) by actual.

The car computer knows the mileage between oil changes,,we reset it. Is this Lexus screwing with me or is there something about oil out there I have been previously unaware of.

I hate unexpected results!

Ray Toews
Fort Vermilion AB

[rwanttaja]

The way I've heard it, you're looking at two engines with significantly different internal operation. The Honda is liquid cooled, runs at a near-constant temperature, and can be built to tight tolerances because of that. The aviation engine is looser, as the engine is air cooled and must operate in a wider temperature regime. Thus more stuff (combustion byproducts, etc.) get into the oil, and aviation oil contains additives that help handle it. The "Dispersant" portion of the "Ashless Dispersant" feature helps to hold that crap in suspension to let the filter grab it.

Ron Wanttaja

[raytoews]

Is the VW engine built substantially different than a Lycoming? The VW in a car should run at a more even temp as it is fan controlled cooled, but when you install it in an airplane??
I assume VW engine guys run autooil??
Ray

[martymayes]

As a second aside,,,I have a 2012 Lexus, I use synthetic oil, and change at 10k kilometers. We ran it over last change by a few thousand and the mileage went from 24mpg to 18. We stop at Mr Lube and the mileage immediately went back to 24mpg. The dash display indicated and confirmed (incredulously) by actual.

The car computer knows the mileage between oil changes,,we reset it. Is this Lexus screwing with me or is there something about oil out there I have been previously unaware of.

Not so much the oil but your Lexus and it's VVT (variable valve timing) can indeed be affected by dirty oil. You see, dirty oil contains sludge which can foul delicate cam phasers and/or control valves in VVT engines. Malfunctioning VVT can indeed affect fuel mileage. If you're not careful, a few thousand past the recommended oil change interval and you can stretch the timing chain. You'll soon get a P0011 or P0021 (left or right bank) code on the MIL (check engine light). That takes some big bucks to get resolved, lol.

Regard your other musings, AD (ashless dispersant) oil used in air cooled aviation engine is supposed to reduce the likelihood of metal ash deposits in the combustion chamber which can lead to preignition. The AD additives are a large chunk of aviation oil cost. Can probably run without it but it's one of those err on the side of caution thingys.

[Mike M]

"7. Automotive oil should never be used in an airplane engine.The most important reason not to use automotive oil in an aircraft engine is the number of additives in it that are designed for use in water-cooled engines operating within a certain range of temperatures and pressures and at constantly changing levels of power. Aircraft engines are air-cooled and operate under an entirely different set of parameters. " ref http://www.swaviator.com/html/issueja02/Hangar7802.html

http://www.avweb.com/news/maint/oil_..._197096-1.html


Etc

[martymayes]

"7. Automotive oil should never be used in an airplane engine.

Back to Ray's point - A VW engine is an air cooled engine. Could it not benefit from "air-cooled additives?"


Here's another angle - How about one of those surplus GPU's powered with an air-cooled Lycoming or Continental engine. What kind of oil do those engines use?

[Mike M]

Is the VW engine built substantially different than a Lycoming?...Ray

Define "substantially" ? Bore on O290 is 1/3 larger than a 2000cc big bore aircooled VW. Larger diameter pistons are more prone to ash deposits and resultant possible damage. So as a NON expert, I don't know. I just read the info and passed it on. Experimental, so have fun.

[Aaron Novak]

Back to Ray's point - A VW engine is an air cooled engine. Could it not benefit from "air-cooled additives?"


Here's another angle - How about one of those surplus GPU's powered with an air-cooled Lycoming or Continental engine. What kind of oil do those engines use?

Long story short, it is a combination of factors that decide a suitable lubricant.

1-Bearing types and materials
2-Seal types and Materials
3-Requirements for EP performance (typically valve and gear train related)
4-Temperature both bulk and at certain locations
5-Operating conditions (transient or steady state, duty cycle etc)
6-Special considerations (climate, corrosion control etc)
7-Control (reducing variability, certifications etc)

1-Lubricants and the additive package have to be compatible for use with the bearing loads, materials, speeds and types. Example : ZDDP attacks the silver used in silver/lead/indium bearings used in some of the larger WW2 aircraft and other engines, and was a common additive in automotive oils in the 1960's through 90's

2-Seal materials and types need different conditioners. Natural materials have different needs than synthetic, lip seals different than flat seals.

3-Certain high contact stress valvetrain and geartrain parts needs EP additives in certain designs. SOme of these EP additives (namely ZDDP) form deposits in the chamber and on valve stems on high temp steady state engines. This is why ZDDP is not used in aviation oils or industrial oils and the oils are called Ashless, meaning no metallic ash (aka ZDDP).

4-Temperature drives what base stocks are used for the oils, how they are cracked and what viscosity improvers are used. Viscosity improvers tend to not handle temperature as well as a good base stock, so air cooled oils tend to use a better base stock and less VI.

5-This connects in with the need for transient friction reduction, deposit formation and time/temperature of the oil.

6-Corrosion control in special situations, engines that spend long periods of storage, high humidity, etc etc. Sometimes special additives for materials like ceramic turbo seals and the like.

7-How tightly the oil is controlled. Auto oils are pretty loose and oil manufacturers have pretty good leeway to make changes without re-certification. Sometimes these changes can affect a particular engine design or useage condition causing foaming issues etc. Aviation oils tend to be much more locked down and consistent.



-Aaron

[Dana]

VW engines in aircraft, as far as I know, usually use automotive oil. My Mosler 1/2 VW specifies 20W50; since the air cooled VW engines were designed in the days when ZDDP was used, I use "racing oil" which still contains it ("not for street use" as the zinc damages the catalytic converter).

[Aaron Novak]

VW engines in aircraft, as far as I know, usually use automotive oil. My Mosler 1/2 VW specifies 20W50; since the air cooled VW engines were designed in the days when ZDDP was used, I use "racing oil" which still contains it ("not for street use" as the zinc damages the catalytic converter).

Dana,
Actually the engine design predates the heavy ZDDP oils by about 20 years. The contact stresses are low enough that the ZDDP has no advantage in that area. You are also running your engine in a manner that is different than automotive. Using an appropriate viscosity aviation oil would be fine, and perhaps a better choice than a "racing" automotive oil.