Motor oil

[Croqueteer]

:confused: The pevous thread made me think as to the pros and cons of using a modern auto oil in a small continental. I have read articles on it in the past, but can't remember the out come. Any ideas?

[javelin]

Don't !

The internal pressures on pistons and other areas of lubrication related to metal content mean that running an aero engine on auto oil is a no no.

You think that modern auto oils are very advanced - they are. The problem we have is we are running on 1940's technology and it needs an oil formulation that suits the engine and it's operation.

I sat on the fence for ages regarding oil and after owning 10 aeroplanes, I now run on Shell multigrade, however, if my useage drops to below 5 hours per month I would go back to good quality monoweight detergent oil - 80 in the winter, 100 in the summer. Multigrade has a tendency to run off quicker and if you are in a normal moist shed or hangar, you will suffer from condensation within the engine which is destructive.

Bottom line, change oil on an hour/date basis - without a filter - 15 hours/4 months, with a filter - 30 hours/4 months :ok:

[stevef]

This link explains why you shouldn't use automotive lubricants in an aero engine.

http://www.castrol.com/castrol/faq.do?categoryId=9001946&contentId=7005219&currentPage=2

Compare the price of a car engine overhaul to that of an aeroplane!

[A2QFI]

Pardon my saying so, I don't think this expains it at all - it tells you not to use it. The text says that automotive oils tend to form ash and might cause pre-ignition if used in an aero engine. Does this ash formation take place with car oil used in a car engine and if it does is that not a bad thing? That said I am never going to buy and use aviation Spec oil in my car but I don't think the stated reasoning is clear.

[BigEndBob]

Similiar arguments go on about using car oil in bikes.
The only thing i've seen in recent years is changes in oil formulation so as not to damage catalytic converters.
Don't think you will ever get an honest answer from an oil company.

[stevef]

Pardon my saying so, I don't think this expains it at all - it tells you not to use it. The text says that automotive oils tend to form ash and might cause pre-ignition if used in an aero engine. Does this ash formation take place with car oil used in a car engine and if it does is that not a bad thing? That said I am never going to buy and use aviation Spec oil in my car but I don't think the stated reasoning is clear.

I think it may well be because auto engines run a lot cooler than their aero equivalents and don't accumulate these ash deposits.

[vector4fun]

Pardon my saying so, I don't think this expains it at all - it tells you not to use it. The text says that automotive oils tend to form ash and might cause pre-ignition if used in an aero engine. Does this ash formation take place with car oil used in a car engine and if it does is that not a bad thing? That said I am never going to buy and use aviation Spec oil in my car but I don't think the stated reasoning is clear.


Point of information;

Years ago, when the price difference between aviation oils and plain old automotive motor oil was not very great, (buying by the case), I ran my old Chevy PU on Aeroshell multigrade for several years, and it absolutely loved it. That truck ran 130,000 miles on that motor before I sold it. For all I know, it's still running....:}

[javelin]

One of the main things is a difference in bearing material. It reacts differently with the oil, I believe the motor oil is more cleaning and can cause problems with aero engines. Your aero engine costs a lot, the price difference between aero oil and motor oil doesn't justify messing around.

This does not apply to Vw's and Scooby Doo engines in aeroplanes.

[Croqueteer]

:) Stevef, I run my 0-200 on a/c oil, but I have still to hear an answer that holds water as to why we cannot use motor oil. Where in the engine does a car engine run cooler? If you are towing a caravan, you definitely need an oil cooler. On the subject of oil addatives, I used Slik 50 in a Renault engined Stampe for 10 years of aeros and aero comps, and never had a trace of metal in the oil, which is unheard of in a Renault. As said earlier, it is impossible to get an answer from the oil companies. I was once asked by a Shell rep why I used BP oil, and when I said it was because BP oil bottles had a built in spout, he was totally bemused. I rest my case.

[stevef]

I've only got a maintenance engineer's knowledge of oils, Croq, but compared to the automatic cooling features on a car, aero engines run extremely hot under some conditions. I suppose a good example would be a hot summer's day: by the time the engine's been run up to operating temperature, the pilot's carried out the mag checks, taxied to the holding point and waited for clearance, the amount of cooling air flowing through the cowling apertures has been minimal. As you know, the engine depends on ram air to keep the temperature down and it's not going to happen until after take off. Pretty hard work on the oil!



I did some idle research into engine lubricants and found the following on an aircraft lubricant site:


'Unlike an automotive internal combustion engine, aircraft piston engines operate much of the time at a constant throttle setting, where the turbulence pattern in the combustion chamber is very consistent. Under these conditions, deposits tend to form and concentrate at points where there is little turbulence. Because the metallic additives used in automotive engine oils promote deposits in these low turbulence areas, they are not acceptable as lubricants for piston engined aircraft.'


These deposits are likely to cause pre-ignition, which will make short work of your engine. Some interesting articles out there.

[Croqueteer]

:O Thanks for the info, Stevef.

[Dream Land]

I seem to remember data from running automotive synthetic oil in an aircraft engine was causing some scalloping, not sure about the spelling, can anyone explain what this is?

[SNS3Guppy]

Automotive oils are not the same formulation at all as aircraft oils. Use the oil designed for your powerplant, period.

You should never mix brands or designations of turbine oils...ever. You shouldn't mix any piston oils with turbine oil. You shouldn't mix automotive oils with aviation oils. You shouldn't use oils designed for one application in a different application, mixed or not.

Automotive fuel and automotive oil composition is not uniform. While ASTM/SAE and other standards exist, chemical consistency isn't the same batch to batch, brand to brand, etc. Avaition oils and fuels are very closely standardized and regulated, and the quality control much tighter. Formulations for a given automotive oil spec vary with the manufacturer, going so far as to have different base oils, numerous different additives, etc.

Aviation oils do not. In the US, the American Petroleum Instritute provides given standards for oil, but allows a wide variety of formulations to meet those standards...and there's no way of determining if the auto oils meet aviation standards (particularly with the variety of formulations and lack of testing).

Aircraft oils stay consistant in formulation and standard. Automotive oils change in formulation constantly, and there is no consistancy.

Why not use automotive oil in your aircraft piston engine? If you're going there, why not just fill it with hydraulic fluid, cooking oil, turbine oil, or oil of oly? Use the right product for the right job. Does anybody remember the Phillips XC debacle about twenty years ago? Or the recent Mobil 1 debacle? Wonder what happens when even small changes are made to the formulation of the oil? Ask the oil companies that shelled out very large sums of compensatory funds for the damages caused.

As for someone who mentioned using Slick 50...do NOT do that. Slick 50 is responsible for damaging far more engines than it's every helped, and it's never helped any. Folks think it does, but it doesn't. It claims bonding of PTFE to the metal parts, but engines never reach a temperature where this is possible. Instead, all the junk in the bottle stays in the oil, occasionally pluggnig oil galleys, filters, etc. Wheather the engine is making metal or not is irrelevant. The US army used slick 50, and forbit it's use after the amount of damage it can cause came to light. So did a lot of other operators. That it's still on the market today is an absolue mystery to me. I would never put it in my car, let alone an aircraft.

[NutLoose]

I am a Licenced Aircraft Engineer and you should not use motor oil in Aircraft engines period.......... the additives in the oils are different and will attack certain types of bearing materials and seals, as well as leaving deposits around the valves.......... put it this way, yes it is a little bit more costly but how much do you put on your life or the loved ones you fly with? do you measure that in pence?...................

I have access to literally hundreds of gallons of Aviation oil through my Job but would never put a drop of it in my car for the same reasons, I would rather struggle and pay for an oil change than destroy my car engine in the long term

[ShyTorque]

I have also heard that adding Slick50 to engine oil isn't a good idea, for an additional reason too. Dupont (who invented Teflon, the so-called effective ingredient) say it has a coefficient of friction higher than that of standard oil and they definitely CANNOT recommend its use in engines.

[Croqueteer]

:confused: My original post did not suggest I was going to use motor oil, but merely trying to find out why a modern highly developed motor oil would be inferior to aero oil in an engine more akin to a tractor engine (and they work all day at high power settings). In UK we can use unleaded motor petrol in the small Continentals, subject to fuel pipes being able to cope with the additives, and I find it difficult to see a problem with the steel, alloy and gasket materials in a small aero engine handling the chemicals in motor oil. The "just don't" brigade do not provide any answers. As far as slick 50 is concerned, a local truck fleet collegue started using it about 10 years ago, and the almost immediate benefit was an increase in cold starting rpm by the starter motor, which does suggest a reduction in internal friction. I put it in my Rover 75 CDT (after the warranty expired) and had an almost 5mpg reduction in fuel burn. It is also in a BMC engine in my boat, with seeming improvement in starting.
My aim in this thread is not to argue, but just to get an interesting and maybe informed discussion.

[Croqueteer]

:cool: I should also had added that cost does not come into this, as good quality motor oil costs about the same as aero oil

[SNS3Guppy]

Rather than "just don't," you were given multiple reasons why you should not use automotive oils. Re-read the posts then question specific points, rather than asking us to repeat them.

Why not just use dish soap?

An aircraft engine is nothing like a tractor engine, neither is it operated the same, or subject to the same conditions. Neither are the consequences for failure the same, nor are the formulations, demands, fuel types, operating temperatures (and changes) the same. Nor the typical frequency of use. Further, as stated before, the oils used in your tractor are constantly changing in formulation, base oil, additives, consistency, and have a large specification which is never tested for, nor proposes to meet, any aircraft specification. Rather than repeat it, read again.

As for using automotive fuels in your aircraft engines, it's legal in some cases, but not very smart. Automotive fuels are not nearly as well regulated nor consistant as aircraft fuels. The same applies to additives. The anti-knock ratings are different for aircraft fuels and automotive fuels, as are the methods used to derive them. Automotive fuels tend to break down faster, leave deposits, can gum up carburetors, selector valves, etc, and tend to cause faster deterioration of fuel bladders and lines.

Why not just fill up your engine crankcase with WD-40, cooking grease, water, marvel mystery oil, or hairgel? Why not just use any additive you like; if it's sold for cars, it must be good for airplanes, right?

Do you remember Phillips XC or more recently Mobil 1?

As an aside, if you use lubricants (not just engine oil) other than what is approved by the manufacturer (both aircraft manufacturer, and appliance (engine) manufacturer), you invalidate your airworthiness certificate and the aircraft is no longer airworthy. Think about it.

[White Bear]

SNS3Guppy reads just like an enthusiastic A & P mechanic who has been properly indoctrinated into his profession.
He is mostly right, but a little misguided in his comments on modern engine oils, and fuels. For example: I have an old pal who has run his 1958 Cessna 172 with a Continental engine on 'autogas' for many years with no ill effects and the FAA's full knowledge and approval. Many thousands of older aircraft fly in the U.S. on autogas with no problems with their engine, fuel tanks, or fuel lines.

Aero engine oils use a different additive package than modern engine oils, as well as higher viscosity base stocks, and they do so for a reason.
Our old fashioned Lycoming and Continentals are air cooled, and that's not the best way to control temperatures. Cylinder head temps often exceed 400 deg f and can go much higher. Modern auto engines never reach those temps. Zinc (an anti-scuff additive) in particular, and the additive that neutralizes acids used to raise the TBM (Total Base Number) of the oil, cause ash deposits in air cooled engines. Higher manufacturing tolerances allowable because of water cooling, and higher comperssion ratios tolerable for the same reason, negate those effects in modern car engines.

The use of heavy weight oils helps significantly in controlling aero engine temperatures, it also takes up the 'slack' in the larger manufacturing tolerances required because of the larger differences in local temperatures, particularly cylinders, front to rear, or top to bottom, and the afore mentioned cylinder head temps, and equally important to the owner, because of the relative lack of use of most aero engines, corrosion problems. Lastly modern auto engine oils are generally of a much lighter viscosity, the manufacturer being more interested in economy, whereas Lycoming and Continental are more concerned about heat control, and less about pumping losses.

If you wanted to use a none aero engine oil, you would probably be better of using an oil formulated for older Harley Davidson's, than modern car engines. The Harley is much closer, as a family member, to your Lycoming, than it is to a modern overhead cam, 4 valve, water cooled, high revving car engine.

Unless your a proffessional, I suggest you follow the these rules for mixing oils: It's perfectly OK to mix oils of different makes formulated to do the same job, i. e. engine oils, transmission oils, rear axle oils etc, provided they are are of the same viscosity. It's perfectly OK to mix mineral and synthetic oils with the same caveats as above. Do not mix oils designed for different jobs, i.e. engine oil and rear axle oil, or transmission fluid with engine oil.
Regards,
White Bear.

[Croqueteer]

:) Thank-you for the informed comment,White Bear, I had already ignored Guppy's rantings.

[Dream Land]

Thank-you for the informed comment,White Bear, I had already ignored Guppy's rantings This guy isn't the one that's uninformed(Guppy), of course you didn't really want an informed answer in the first place, did you. :ugh: Good luck with your engine.

D.L.