Engine oils?

[ZeBedie]

Back in the day, engine oil was the yellow tins of Shell W80 or W100. Now that modern multigrade oils have been available for Lycomings for some years, I wonder if this has produced an increase in engine life and a reduced rate of failures, or not?

[phiggsbroadband]

I was once talking to an 'oil technician' who tried to convince me that modern oils are the Bees-Knees, and that instead of being just the product of the Catalytic Cracker, are now a sophisticated blend of compounds. He tried to assure me that this was the reason why engines now have such a long life.


However the Japanese (Honda) started using some very special alloys for their pistons and castings in the 1970s, instead of the almost pure aluminium used by British engineers. This resulted in very much shorter running-in periods. (50 miles as opposed to 500 miles.)
I don't know how much Plain Big-End bearing material has altered, but suspect it is probably slightly better now.


All other components in an engine are either caged Roller-Bearings, or Case hardened Nitrided Steel, for the crankshaft, camshafts etc. Same as could have been used in the 1930s.

[piperboy84]

Zeb, Are you saying the Aeroshell w80 I used to buy up until last year in the yellow 25 litre drums is different from the W80 I get in black plastic 1 litre bottles now?

[Above The Clouds]

One advantage with the Aeroshell 15w 50 multigrade oil is it doesn't require the additive recommended by Lycoming to reduce camshaft pitting. Been running my 20 year old Lycoming on it for sometime now without any problems, the oil consumption is minimal and oil pressure has not changed in 3 years.

[Curlytips]

I've read various comments pro and con multi grades versus traditional oils, but have always used multigrade to avoid having to change with the seasons. Moreover, if you want to run on UL91 Lycoming service bulletin demands that you use Aeroshell 15/50........

[A and C]

You are only partly correct, Aeroshell W80 plus and W100 plus can also be used with 91UL.

[Johnm]

On our IO540 we have to use XPD80 if we want to use UL91, multigrade is fine, but not really necessary in the UK as the temperature extremes aren't usually that significant. We use W80 with Camguard all the year round.

[onetrack]

phiggsbroadband is correct. There have been major advances in both oil technology and engine materials used in construction in the last 30 years. However, it's the auto industry that is leading the developments.
Aircraft engine designs are very slow to change, and new aircraft engine construction materials slow to be introduced, due to the need for extensive proving and certification.
The newer improved oils have probably had some impact on lengthening piston aircraft engine life, but it's a moot point when you have overhauls set on fixed hour limits.

Multigrade oils are base lubricating oils with "viscosity improvers" added. These VI's are long chain polymers that have the curious (advantageous) molecular properties of molecules lengthening as they cool and shrinking as they heat up (conversely to what you'd expect).
As a result, they thicken the oil viscosity when hot, and thin it when cold. This allows the base lubricating oil to perform better over a much wider temperature range.
Oil industry chemists then add additional chemicals to the oil that improve lubricity, that soak up and neutralise contaminants, that prevent corrosion and foaming.

The search is on constantly, for newer chemical additives to oil that increase the lubricating oils ability to deal with increased bearing pressures, to cope with higher levels of oil shear, and higher levels of contaminants, and to reduce oil burn.
This is the area where the greatest developments have been in oil in the last 30 years - in the improved polymers and additives that are available today, as compared to the 1960's and '70's.

[Curlytips]

I bow to your superior knowledge. After checking, SI-1070 only specifically names Aeroshell 15-50 but states "other equivalent finished products" - presumably containing the necessary additive - are acceptable. Both the plus have the additive yet the Shell site doesn't mention conformity with 1070 along with the other approvals it shows.

I think when I first looked at this and started using UL91 it was SI-1070R not the current 1070S and it was when the future looked rosier because unleaded was considerably cheaper. Now my UL91 stickers next to the filler caps are fading and I doubt I will renew them since regular Avgas is now cheaper :bored:

[Big Pistons Forever]

All the oils do a decent job. Way more important is that you change it regularly, especially for airplanes that do not fly several times a week. I change the oil in my Grumman AA1B every 6 months regardless of how many hours it has flown.

After six months the oil will be full of nasty acids, combustion byproducts, lead, etc etc, none of which is good for you engine.

I use Philips 25W60 in my Nanchang. I find that unlike straight 100, you get instant oil pressure as soon as the engine starts and it takes about half the time for the oil to reach operating temperature after start, compared to 100.

[Thrust Augmentation]

I think if modern multi grades increase life or reduce failure will vary from case to case, depending on usage. It obviously has advantages where temperature fluctuations are considerable, but may have disadvantages when the aircraft is used infrequently.


Mono's are heavier at lower temperatures & when the aircraft sits unused will tend to remain coating the internals for longer than a multi grade. Multi's as they remain thinner will more readily drain & leave internals unprotected from corrosion. I imagine that start up wear may be a concern with dry internals (is there any sort of oil priming on an aero engine?).

[Jan Olieslagers]

Yes: hand turning the prop a few turns. I always do so, on my Rotax 912.

[dubbleyew eight]

big pistons we have all heard the litany of acid oil claims but have you ever verified the claims?
you have to beware of information "that is common knowledge"
because sadly quite a lot of it is marketing hype / bull****.

I am a pariah.
I test the ph of my oil.
I use phenolphthalein as my ph indicator.
it is available in australia in a soil test kit out of Bunnings (our version of home depot) for about $aus 20.
you need a white surface.
you put a coupe of drops of oil on the white surface then a drop or two of phenolphthalein and smear the two together over the white surface.
you then read off the ph from the colour chart.

normal aircraft oil is ph 7 brand new out of the bottle.
never ever in all of my tests have I found my aircraft engine oil to be acidic.
so I call Bull**** on all the acid oil claims.

my engine was designed for 50 grade oil.
I have used aeroshell W100, Castrol Aviator D100 (the best) and now Phillips AW100 without any problems at all in my O-200.

verify the claims son. most of them are bollocks.
W8

[onetrack]

Acids are a regular byproduct of the combustion process - but more than one of the additives in engine oil neutralises the acids and renders them relatively harmless.
However, that is IF, the acids have reached the oil.

Acids from combustion can be retained in the engine - but not necessarily in contact with the oil held in the crankcase.
I have seen big end and main bearings, and crankshaft journals, etched by acids - thus showing that acids do settle in parts of the engine in amounts that can do damage.

The best thing you can do with any component that relies on regular lubrication is to start it or move it on a regular basis, to ensure the oil is thrashed around and coats all the important surfaces.

The oil draining off the surfaces of crucial components such as camshafts and cam followers is definitely a major problem - and corrosion can often form on these surfaces in as little time as several weeks.

[Big Pistons Forever]

verify the claims son. most of them are bollocks.
W8

Oil is cheap, engines are not. Acid is only one of the nasty combustion by products that will be captured by the oil additives. You want to leave that crap in your engine, fill your boots. Me, I think I will give her some nice fresh oil on a regular basis.:ok:

[Above The Clouds]

For what a few litres of oil costs in my view is not worth considering. I change the oil on my lycoming every 25 hours or 6 months whichever comes first, still running the same +20 year old engine now 350 hrs past TBO with no signs of trouble.