| Shazam,
good to see someone has excellent knowledge about oils... anyway here goes...
Motorcycles are harder on oils for the fact that they rev higher than cars and this means that the effects of oil shear are greater, particularly in Big end bearings, and gearbox parts, as the parts move more dynamically.
The biggest degraders of oils in any engine are-
1. heat, effects of combustion products, and finally degradation through mechanical shear, this being from the oil 'tearing" as it separates from metalic surfaces.
oil is required to basically -
1. lubricate
2. cool
3. clean
Motorcycle oils like any automotive oils have additives to combat this, namely the likes of lithium, detergents for engine cleaning (internals), phosporous, friction midifiers, zinc, and a few years ago even lead (extreme pressure additive), but lead is now replaced with polymers.
Every manufacturer has their own additives, but generally are based on the above, although zinc, phos and lead are diminishing (lead has gone).
As you rightly mentioned, viscocity does diminish quite quickly (relatively), and this is due to heat, and shear exposure.
During the first few revs of an engine, when boundry lubrication exists (this is when you a very thin film of oil between metallic surfaces), this is when we experience most mechanical wear, until full lubrication is achieved (hydrodynamic lubrication), and the oil is up to normal temp ie operating temp.
for change intervals, modern oils are able to achieve longer miles between changes, simply due to their stability from the addition of modern chemicals.
I agree that changing your oil on a more regular basis is a good thing, but not essential. Bike manufacturers give change intervals after their engines have been on a test bed / dyno, and after a specified time an oil sample is taken for analysis. Thereafter the manufacturer will decide upon the interval.
Did you know that the earlier oils from the PAH group of products can be carcinogenic. The PAH stands for poly - aromatic hydrocarbons, and is your basic mineral oil. Years ago oil companies issued data sheets with their products to outline the problem with PAH, and recommended full hand protection, and in some cases, face masks when handling these USED oils.
Here is a word of warning, when conducting oil changes / or handling oils, always use rubber gloves, to prevent the PAH's from entering your skin and dispose of properly.
TO SUM UP - Dont go over your oil change interval unless you really have to.
always use the manufacturer' recommeded oil grade (visc), or better, but if you have a jap bike with a wet clutch, you may void your warranty / cause damage to your clutch due to the inclusion of friction modifiers / polymers in semi, and fully synthetic oils.
I use fully synth in my duke, and semi im my yam r6, and depending on use, change the oil more regularly, simply because I can.
Mobil 1 has now been out for a good 15 years on the market, but has been under test some 5 years before that. We tested this oil in various applications, particularly high revving engines, both cars and motorcycles, and it was found to have excellent visc stability until the addition of friction modifiers, particularly a certain polymer, so a comprimise was agreed upon.
Whilst we are on the subject of oils / fuels, did you know that the jet engine used in airplanes actually uses diesel ?
The fuel, jet - A1 is a derivative of the napthane group of oils, and is a highly "cracked" product of crude...basically kerosene.
next time your at the airport and smell fuel in the air...what does it smell like ?
Whilst on the subject of "whose oil is best" people go around ranting that shell is best, or BP is no1, let me tell you that the oil majors carry each others oil in the tankers you see on the high seas, however its what happens to this oil at the respective refinery that makes the final product.
Also certain crude base stocks from the 8 different main supplies around the world are used in different ways to produce different end products, say Arabian light crude for fuels, Brazilian crude for fuels, plastics, mineral oils etc...each has its merits.
did this help.
demon - E/Mobil marine oils  |