Originally Posted by 90crvtec,Dec 8 2006, 02:40 PM

Do you have evidence to prove this? My understanding is that Honda recommends oils that are either 10w30 or 5w40. Provided that the oils perform to these specifications I don't believe Honda mandates that they be dino or synthetic. Finally, I haven't seen a non-synthetic 5w40 oil, that's a pretty big viscosity spread and I'm not sure a dino could pull it off with the needed sheer stability.

Originally Posted by RACER,Mar 4 2005, 04:17 AM

To make a 10w-40 oil, the manufacturer would start out with a 10 weight oil as the base stock. All by itself, this oil would thin out so much at normal operating temperatures that the oil film would be useless. So, they add these very special very long molecules, the VIIs. The VII molecules are as much as 1000 times as long as an oil molecule. The VII molecules curl up in a little ball at room temperature, but as the temperature gets higher they uncurl and stretch out, like a cat sleeping in the sunlight. The more stretched out the molecule is, the more it impedes the normal flow of the oil, thus raising the effective viscosity. Now, this sounds just a little too good to be true. Well, there are two catches: first, these molecules are not lubricants, so the more of them that you add the less oil you have sitting around lubricating things. Secondly, these VII molecules can be broken into pieces by various pressures and forces, like being squeezed through the transmission gears in a motorcycle or the hydraulic valves in a diesel engine. Every time a VII molecule gets broken, the oil loses some of its high temperature viscosity. Synthetic oils made from pure PAOs and/or Diesters typically have very few VIIs, so these oils are far less subject to viscosity breakdown due to shearing of the VII package. As a result, synthetics are far more stable in a motorcycle engine.

10w-30 oil increases its viscosity at high temperatures by a factor of three, which requires a significant amount of these VII molecules. 10w-40 oil increases its high temperature viscosity by a factor of four, which requires even more even longer molecules. 20w-50, which sounds a lot like 10w-40, only increases its high temperature viscosity by a factor of two and a half, so it requires fewer of these molecules than even 10w-30. 15w-40 also increases its high temperature viscosity by about two and a half, so this oil is also substantially more stable than 10w-40. Most passenger car oils today use inexpensive VII molecules that break apart relatively easily. Conversely, most diesel engine oil VIIs are chosen from more expensive chemicals that are more shear stable, since an oil change in a large diesel is expected to last for 15,000 to 150,000 miles.

Viscosity is not actually measured in "weights", but rather in units called "Stokes." If you're a famous scientist they name a unit after you, except for poor Albert who is considered famous enough all by himself. Stokes was a guy who worked on fluid flow. For oils, we use a hundredth of a Stoke, called a centi-Stoke, abbreviated cSt. "Weights" are a classification invented by the American Petroleum Institute (API). A different unit of viscosity, the centi-Poise, is used at very low and very high temperatures. 10 weight oil refers to oils within a range of viscosities, so two different brands of 10 weight oil might actually be quite different. 75 weight gear oil is actually about the same viscosity as 10 weight motor oil. Don't ask me why, I'm not a petroleum engineer; although some might argue that I do belong in an institution.


There you have it, 5w-30 is lighter than 10w-30. Because of the fact that 5w-40 has more of these molecules that do not lubricate, I will stick with 5w-30 or 10w-30 motor oil.

Originally Posted by brimstone,Dec 7 2006, 10:56 AM

AE Haas disagrees with you, track and autox operating conditions seem to be ~312F, if I recall correctly.

I went ahead and assumed that continous high-revving and high-speed conditions are similar, although I can see how the cooling system might work very well under those conditions.

Still, the way I run my car night after night on the highway, I wouldn't be able to sleep if I ran xW-30.

Look, here's my logic:
What ever operating temperature cSt Honda found to be suitable for this car, its somewhere between the ranges of a 30 weight and a 40 weight oil. I feel my conditions are rough, and more prone to sheering than 65mph cruising, and I feel more comfortable being on the thick end of the spectrum.

Now, I do wish I could find a 0W-40, but that is proving to be a hard task.

Originally Posted by hecash,Dec 13 2006, 02:11 PM

VAD see........order it