DSinger,
Why do you think this?

The only caution I would add to the use of multi-weight is try not to cover a wide range of parameters with one oil. The buffers/medium that enable one oil to behave well from low to high temperature extremes does not contribute to lubrication themselves. Also, this is the substance that is first to 'coke-out' when exreme temperatures are encountered. In other words, instead of using 0-50w, try 10-30w or 20-40w. Most aircraft oils encounter some pretty high temps since the engines are air cooled and find themselves in some pretty tight cowlings so a great deal of pilots prefer a straight single weight, such as 80 in the northern climes and 100 in the south. This lessens the chance of oil breakdown. FWIW. :)

Viscosity Is Relative, Not Static...
 

First, read your owner's manual as regards recommendations for viscosity. The viscosity of a multigrade oil is determined by the climate you operate in, not just the year and model of car. For instance, I live in California, and for my cars, I need to use a higher viscosity rated oil, like 15W50. If I lived in a cooler climate, I could use 10W30, or even a 0W40. The "W" stands for "Winter", not "Weight"...

Some extremists believe that a 0W40 will work better for them even in California, because they think that the oil is at 0 viscosity when the car is started. That would only be true if the ambient temperature were cold enough to cause the oil to flow at 0 viscosity. If the temperature were say, 56°F, wouldn't the oil actually be about 10, or 15 anyway due to the rise in temperature from where the oil would be flowing at 0 viscosity? I don't know that answer yet, but I'd like to, so I will try to find out just what the temperate spread is on a multigrade oil.

The flow characteristics of a 10w-40 oil matches what a straight 10 would do in cold ambient temps as well as a straight 40 at the higher temps. And yes the w stands for winter but is referred to as weight (why, I don't know). I don't know why the 80 weight aircraft oil is actually referred to as 40 and the 100 as a 50, either. Perhaps there is a 'proof' involved in aviation. ;)

Longston, what dynamic behavior do you profess that oils possess?

Yes, But...
 

What I mean is at what temperatures does the oil exhibit characteristics of increased viscosity, and to what degree?

For instance, 10W30 is at a viscosity of 10 between what two temperatures before the polymers that make up the viscosity improvers cause the 10 to shift to a 15, or a 20, and then to 25, or 30?

And the numbers associated with aircraft oils are derived from the Mil. Spec., or Military Specification #. So, 30 weight, is actually Mil Spec. 1065, or commercial aviation # 65, while 40 weight is Mil Spec 1080, or commercial aviation # 80, 50 weight is Mil Spec 60, but commercial aviation # 100, and 60 weight is Mil Spec 1120, and commercial aviation # 120. Rememeber pilots, "proof" is never a safe thing in aviation. "12 hours from bottle to throttle" is a safe rule...

Multi viscosity oils should never be referred to as 10-weight-40. This is a misnomer carried over from single weight oils that are referred to as "30-weight", or 40-weight. 10W30 is simply, 10-30...

Yeah!....what he said! ;)

longston
 

Are you of the opinion that multi-grade oils exhibit changes geometrically from the low end to high end of ambient temperatures as opposed to directly proportional?

For all FSS cars:

The factory fill for 98's was pure dino oil.
For 2001's the factory fill was switched to synth/dino blend. Sometime in 2001 the factory fill was switched to pure synth. The switch was made right after the "recommendation" to switch to synthetic oil.

Kuan

Hi Guys!

My W-140 92'300SEL runs on CHEMLUBE 10W-30 and is now running into 123K miles.

Best oil I have ever experienced with the engine silky smooth.

Comments from members who have tried CHEMLUBE!

Try it and you will feel the difference.

Happy Motoring.

Actually...

Assuming you gathered some data and managed to get some points. At low temps, they will fit a straight line. At another temperature, they will fit yet another different straight line.

Kuan

Kuan, to what are you correlating the value of temperatures to plot yet a different function?

Sorry, I thought we were talking viscosity here. Never mind me... :D

Kuan

Oh, I thought you had something there I had not run across. ;)

So from what I read, I drew 2 conclusions
correct me if I am wrong

For synth..
thick oils like 15-50 should be used in hot climate?
while 10-30 or 5-30 should be used in cold climate?

does that apply to the FSS cars...for 98-2000 models i mean