The International Cessna^® 170 Association

I currently use aeroshell 15w50. An A&P, working on the 170 parked next to mine, suggested using Mobil 1 synthetic oil(the kind for cars). He felt it was better than mineral oil. Some flying buddies use Phillips 20w50 and thought it is a good choice. I'm all ears!

Tell the A&P next to you to go jump in the lake!
Never use automotive oils in aero engines for several reasons.
1. They do not contain lead scavengers. Your aero engine most likely burns Avgas, if not all the time, at least part of the time, and auto oils do not contain lead scavengers. (That's why Mobil's aviation Synthetic oil was removed from the market over a decade ago. Engines were being ruined by excessive lead buildup because synthetic oils do not scavenge well. That's why Shell 15W50 is a semi-sythetic... It has mineral oil in it also.)
2. Auto oils contain zinc and phosphorus additives. The zinc is intended as an anti-scuffing agent for auto engines. That's fine, except the aero engines don't operate at auto engine rpms and don't suffer from scuffing. The zinc eats up the babbit material in your main and rod bearings, not to mention your thrust bearing (which takes most of the strain of your prop pulling you around. There's also a lot of zinc in aftermarket auto additives, "snake oils", such as STP, friction proofing, Motor-Honey, etc, etc. You don't want that stuff in an aero engine.
The phosphorus is another additive found in auto oils. It will form an ash when burned. (Remember, aero engines are not as tight-fitting as auto engines. That's why they consume oil at greater rates than auto engines.) When that oil gets past your aero engine's rings and burns in the upper cylinder, the phosphorus makes ash that will glow in the dark, and cause pre-ignition. Phosphorus is not found in only SOME auto oils, it's found in virutally ALL auto oils. (It's how accident investigators determine whether auto oil has been used in an engine, ...the phosphorus leaves tracers behind that you can't get rid of.) Again,...DON'T use auto oils in aero engines.

You don't say where you're doing your flying. We've discussed this issue in other message threads here, and you might want to click on "search" to look at those previous discussions. If you are in temperate climates, then multi-grade oils will not likely do much for you. A straight-weight SAE 40 oil below 40 degrees F, and a straight weight SAE 50 oil above ambient temps of 40 F, is most likely your best selection. (The SAE 50 straight weight will allow an increase in oil temp red-line from 225 to 240 F. A multigrade oil is not permitted to do that increase.)
A multi-grade oil is great in cold climates where it is impractical to pre-heat your engine prior to starting. Otherwise, in my opinion, (and it's only an opinion but one I'm very confident in), you're wasting your money and very likely not providing your engine with the best choice in lubrication.

i knew i would hit paydirt here. it seems as if there has been a shift towards straight weight the last few years. when i first got the plane the prevailing opinion was multigrade, and aeroshell was the best. i've asked a number of knowledgable people the last few days and i think straight weight seems to be the way to go...but keep those opinions coming.

I live in northwestern Washington,which has a pretty moderate climate. In spite of our lack of extreme temps,I like Phillips 20-50 for most of the year,and Aeroshell W100 for the summer.
I buy my oil from a local petroleum distributor,and the price was just about the same last time around--in fact,the Aeroshell was more expensive ($31.08) than the Phillips ($30.26)!

Eric

One more comment about multi-grades,....
A 15W50 oil is a SAE 15 weight oil with additives to make it behave like SAE 50 when it's hot. In other words, however thin 50 wt is when hot,...that how the mulitgrade 15W50 is at the same temp. This is fine when all those additives are fresh and young. After the oil starts deteriorating, you'll find your oil behaves like the SAE 15 it really is. That's one reason after about 20 hours your oil consumption increases. The additives are giving up. It's also why it seems to leak more.... It's really 15 wt and it fits thru the gaps and drops onto the hangar floor easier than thicker oil.
I'm not knockin' the stuff... It serves a purpose and has a place. Like when it't coldern' a witches' tit (that's a technical term)... and you don't have time to preheat. But it will never protect engine parts as well as higher wt oils when the going gets tough.... And Shell knows it. Aviation Consumer had a very interesting article about this issue not long ago. Shell had egg on their face when they found out that SAE 30 engine oils showed less wear than SAE 10W30 oils did, and the reasons are as stated above. Just FYI. Use it as you wish.

After checking with a friend who manifactures lubricants, including synthetic one's, I have to disagree with some of the statement's that have been written.
1) Synthetic lubricants share the same detergents as their mineral conterparts. Do you have anything to substantiate the previously stated fact that these lubricants do not contain lead scavengers?
2) Although "Auto-oil's" does contain zinc, the babbit will be eaten up only if they are made out of silver.

Regarding the mutigrade oils: about 25% of the oil is the thickening agent responsible for the multi-grade effect. This additive is not a good lubricant...[/quote]

Eric Leclercq wrote:After checking with a friend who manifactures lubricants, including synthetic one's, I have to disagree with some of the statement's that have been written.
1) Synthetic lubricants share the same detergents as their mineral conterparts. Do you have anything to substantiate the previously stated fact that these lubricants do not contain lead scavengers?
2) Although "Auto-oil's" does contain zinc, the babbit will be eaten up only if they are made out of silver.

Regarding the mutigrade oils: about 25% of the oil is the thickening agent responsible for the multi-grade effect. This additive is not a good lubricant...

[/quote]

Disagree all you like, and go with whatever your friend says. Ask your friend if he knows anything about the Mobil Av1 synthetic that caused an Airworthiness Directive all on it's own about failure of that oil to scavenge lead, the engine failures it caused, and the multi-thousand dollar settlements Mobil made with owners over it, the numerous new engines they had to buy, and Mobil's removal of their synthetic from the market, and refusal to re-introduce a synthetic aviation oil for piston engines. It was the manufacturer (Mobil) who brought the propensity of synthetics to fail in scavenging lead to everyone's attention! I don't personally need any more confirmation than that, but nevertheless there are numerous studies besides Mobil's own in-house studies that have since confirmed that fact.
"Synthetics share the same detergents as their mineral counterparts..." Oh, Yeah? Which ones are those? Tell me. Which brands, and for which intended applications are there that use both synthetics and mineral oils that share the same additive packages. Be specific. I really want to know.
Do I have anything to substantiate "the previously stated fact" that these lubricants don't contain lead scavengers? Let me ask you...do you know of any modern auto fuel sold in the US that has lead??? Why, I ask you, would anyone include a lead scavenger in a product intended to be used in a No-Lead environment?
But nonetheless,... I don't have to substantiate it! The manufacturer of that oil stated that was the case all on their own! I'll take their word for it! Mobil specifically stated that was the reason they withdrew their synthetic aviation oil from the market, and further, they even stated there was no way they could modify a synthetic to make it compatible with leaded fuels! Why do you think Shell's multigrade is a semi- synthetic? Because only by including a mineral-based oil with it can they assure that lead buildup will not become a problem because synthetics won't absorb those contaminants and remove them from the engine. Only mineral-based oils will. (Shell even has a position-paper that describes this very issue.)

I don't know where your friend gets his info about "silver" babbit bearings in aero engines, but there are several respected publications that have documented the loss of material (copper) from aero engine babbit bearings (mains and rods) due to the use of additives found in auto oils. (And Shell multi-grade and Shell Plus oils are almost as bad.) Aviation Consumer, Light Plane Maintenance, and Shell Oil Company's own research department has quite a library of documentation regarding this matter. (And zinc isn't the problem with leaching copper out of bearings... Phosphorus is. Zinc's problem is an entirely different one regarding bearing material transfer (commonly referred to as galling.) But don't take my word for it. Ask Pratt and Whitney who is adamant that if you use an oil containg zinc in their piston engines they specifically deny responsibility and you are on your own! They are very specific that it will cause failure of the master-rod bearing!) But don't stop using whatever auto oil you apparently have already decided to use just because it's not approved for airplanes, and just because aviation authorities decry it, and just because good sense dictates. Go ahead and do whatever your "friend" says.
If, as you say, "about 25% of the oil is the thickening agent responsible for the multi-grade effect. This additive is not a good lubricant..." , then just what are you saying? Are you saying that multi-grade oils are 25% no good for lubrication? If you believed your own statement you'd have to have a death-wish, or at the very least have minor orgasms when buying overhauls to use an oil that you had prior knowlege suffered a 25% loss of lubricity.
Whooo-Boy. Ok, Geo,...calm down now....

i am enjoying the discussion and am learning quite a bit. thanks all.

I am aware of individuals who have run nothing but auto oil in aircraft engines. It was quite common, these guys ran them hard in very cold conditions abused them to no end even beyond red line and never had problems with them. Ran them past the TBOs. These applications were in snow planes, the fore runner of the current snow machines. They are a pusher sled on skiis that use an aircraft engine. The early O235 O435 and C series of engines were used exensively in these applications run completly on auto gas and auto oil.

I am also aware of individuals who have run the O300 and C145 beyond TBO on nothing but auto gas and auto oils.

The local fish and game guys have a pusher marsh boat with a C90 run on nothing but auto gas and auto oils. They bring it in to the A&P for maintenance each year. They literatelly abuse it, but the compression and oil consumption remain good.

I suspect in an emergency, one could use auto oil to get you out of a bad spot. But running it to replace aircraft grade oil - you would be a test pilot.

In an emergency I suspect if you find the cheapest straight weight auto oil on the market with no additives it would be roughly equilivant to the straight weight mineral oils.

First, it is not because one company failled, that all of them, have to be dropped in the same basket...Sadly for the aircraft community, due to expensive certification cost, some technologies tends to take forever to reach our aircrafts.
Yes I will try to get you more info on your questions and yes the thickening agent IS not a GOOD lubricant...
(By the way I ran my race bike for years with avgas and synthetic lubricant's)

I have to admit, I've often wondered what the difference was when breaking in a new engine, between running aviation "mineral" (meaning non-additive) oils, and using automotive "non-detergent" (meaning non-additive) oils. You'd think that if both were only refined motor oil from mineral base-stocks sans additives of any kind, that they'd equally be just fine to use when breaking in a new aero engine.
On the other hand, ...just to save $10 or $15 bucks just for 25 hours of operation, while risking the unknown on a $10,000 or $20,000 engine seems a bit foolish, so I still use AeroShell non-AD oil for break-in. (Call it cowardice.)
N1277D...you make a good point. Of course using auto-oils exclusively when using autogas exclusively doesn't offend my sensibilities nearly so much as using auto-oils in engines that use leaded AvGas, (for the reasons previously tiraded upon.)
If I'm not mistaken, Blue Leader used motor oil (Definition: Motor oil is automotive lubricant, Aero Oil is Aviation lubricant) in his C-145 at one time. I'm hoping he'll jump in here and let everyone read his opinion.
PS: If I were somewhere out in the boonies and couldn't find aero oil, I'd have little problem using Non-detergent, Mineral-based auto oil as a make-up to get a sufficient oil level in the sump to get it home. I wouldn't use detergent or additive types though.

As far as I am concerned I would do the same (buy the aviation brand) for the simple reason that you know what is not (in this case ) in the oil...One of the problem with some automotive oil is that some company's (usualy the cheap one's) play with word's regarding the content.
Example: Some advertive their oil's as synthetic when only part of it is.
That is one of the problem's some decent oil manifacturer's have, when selling their product.

I spoke to the friend I talked about earlyer, He agreed to a meeting next week to give me more info (constructive) on this subject. He is the president of the company and a busy man...However, he has been alway's patient with all my question's in the past...
Cheers

Aeroshell sells for about $2.50 a quart when you buy it by the case. Car oil is about a buck? Figuring an average use of about 10 quarts per cycle--7 or 8 at oil change,plus another couiple over the course of 25 hours--you'd save maybe $15,or about 60 cents an hour. Think I'll stick the approved stuff.

Eric

This is the info I got after my meeting this week. First of all there are three families of synthetic oils in the automobile industry:
1) Esters;
2) Olefins; and
3) Glycols.
The last one is only used in two-cycle engines. Mobil used the Ester family many years ago in their first synthetic oil and it made the engine seals swell… It was removed from the market early on and replaced by an olefin based (Poly alpha olefin, to be precise). The ability to get rid of the lead in an airplane engine has nothing to do with the detergents but with the polarity of the oil. It seems that the stronger the polarity, the better. Mineral based oils have good polarity so they are able to “stick” to engine components, preventing the lead (less polar…) from doing so. The Esters are more polar than mineral oils, the Olefins are not… If you use an olefin-based oil in an engine running avgas, the lead will deposit on all metal surfaces. Some companies add a certain quantity of Olefins in an Ester-based oil to neutralize it’s detrimental effect on seals; such oils will be able to take care of the lead problem. Ester based oils are also used in aircraft turbines (they will make seals swell if used in a piston engine).

Regarding zinc and babbit, Pratt radial engines have some of their components plated with silver (still trying to find out which…). The phosphorus is found in small quantity in some oils but it “should not” create any problem.

As for the multi-grade agent, its quantity will vary proportionally with the desired range of viscosity. As an example, synthetic oil needs about 6% in 10W30 and up to 25% in 5W50. The mineral oils require more because they tend to lose their viscosity (with heat) faster then their synthetic counterparts.

To end this note, if someone still wants to use car oil in their (let’s say) “homebuilt aircrafts” with avgas, I would suggest doing continual oil analysis.

By the way, does anybody know what happened to the synthetic oil Amzoil had on the market in the 80’s

Eric

Just a Quickie, I maintained a PA23-235 for a fella who owned a certified oil analyisis company for fleet and aviation. What it came down to from oil analyisis was that mineral did what is said it would, AD oil would do what it was suppose to do, shell multi viscoscity and phillips XC multi would multi viscosilate or what ever they did. So he used mineral for new engine break in single grade AD oil for the summer and multi visc for the rest of the year. however His analysis showed that the phillips had qualitys in that he like so later on we ran it in both of his birds all year, plus I liked the color of the can .
Vic