The reason for the light weight oils isnt so much cooling as it is gas
mileage. And it's not as big of a deal in a rotary as it is the piston
engines. I personally can not fathom running a 5 weight oil in any engine,
so I don't. I'll give up a little gas mileage.

Bob Mears
Supermarine spitfire

Yes - the trend to lighter weight oil is about fuel economy.  The anti-wear
performance standards have been strengthened to keep wear in check as the
viscosity is lowered.

Synthetic will run cooler than petroleum - less friction, and better heat
transfer.  Generally we can go up or down one viscosity grade and have good
performance from the oil.  Dropping two or more grades can significantly
increase wear.  Rising two grades eats power, increases heat, and in extreme
cases can cause oil starvation in bearings.

5W-30 isn't a SAE 5 oil - especially when synthetic.  The SAE 30 is a
kinematic viscosity measurement - actual physical 'thickness' at a specified
temperature.  For engine oil, this temp is 100C/212F.

The 5W is an 'apparent viscosity' measured in a cold-crank simulator (ASTM D
5293).  The torque transmitted by the oil in the test is compared to the
performance of straight-weight petroleum oil measured at the same
temperature.  5W doesn't necessarily mean the oil has an SAE 5 kinematic
viscosity.

Additives can be added to petroleum to change the cold properties, and
viscosity improver additives are needed to keep petroleum from 'thinning'
when hot.  Generally, synthetic base oils don't have the thickening issue
when cold and don't need viscosity improver additives to 'thicken' the oil
when hot.

0W- oils are tested at -35C, 5W- at -30C, 10W- at -25C, 15W- at -20C, and
20W- at -15C.

There are synthetic SAE 30 oils on the street that also meet 5W-30 and
10W-30 requirements without the use of cold flow improvers.

I bought and lab tested Idemitsu 10W-30 in March '05.  Here's the
spectrographic data (in parts per million per ml) and physical properties:

Iron 1
Chromium 0
Lead 0
Copper 0
Tin 0
Aluminum 0
Nickel 0
Silver 0
Silicon 2
Boron 1
Sodium 1
Magnesium 13
Calcium 1604
Barium 0
Phosphorus 1081
Zinc 1246
Molybdenum 227
Viscosity/100C 10.17
TBN 5.87

Viscosity is in the lower 1/3 of the SAE 30 range (9.3 - <12.5 cSt)

http://www.idemitsu-usa.com/page_216.htm
http://www.apolloamerica.com/images/specsheet10w30.pdf

The datasheet reports CCS viscosity at -15 (2090 cP) and -20 (3420 cP), but
not the -25 required of 10W- oils.

This oil appears to be a PAO/ester oil as advertised.  Cold crank is a bit
high compared to other 'real' synthetics, but it's hard to compare since
they report non-standard temperatures.  Viscosity index is decent.  I'd like
to see high temperature/high shear.

This isn't the same oil referenced in the SAE paper on LeMans oil
development, that's for sure.  The benefits/description of the oil listed on
the Idemitsu-USA website are true for any man-made synthetic oil (Mobil 1,
Redline, AMSOIL) when compared with petroleum.  Molybdenum by itself doesn't
guarantee reduced friction.  There are oils on the streets with moly that
have higher rates of wear than the same company's oil without moly.

For aircraft use, especially because we share a gearbox with the sump, I
think that high-quality synthetic motorcycle oil is the way to go.  Probably
10W-40 rather than 20W-50.  Synthetic motorcycle oils are designed to stay
in grade when lubricating gears, are designed for high-rpm operation, and
are designed for wide temperature extremes.

Andy Hecker

Andy,

It looks like you are a bit of an oil expert.

What is your take on Mobil 1 vs.  Redline vs. AMSOIL (in no specific order)?

I personally have never viewed them to be equals, but would like an expertâ??s opinion.

Thanks,
Heath Holbrook

Hard data Andy :) Compositions if you have them.