Okay...

This is what I wanted to say about oil & viscosity.

My answer will not stop the oil debate.
But I hope it will clear some things up.
Here's a list of several brands & popular viscosities at -20C - +20C in 10C steps.
The specs were taken from the oil manulfacturers website.

Suppose you're driving around with Mobil1 10W-30 and after reading AEHaas's website about thin=better oil you decide to "go thin" with German Castrol 0W-30.
You're actually using a thicker oil.
INDYMAC, you conservative WHIMP

There are more examples where it all depends on the start-up temp IF a 5W-30 is going to give you much benefit.

The difference between a true syn or "Synthetic" oil is IMO also important.
True syn oil will be better and/or longer heat resistant and will most likely shear down less.
Look at the VI's, some oils with the same SAE specs have very different VI's.
IMO thats an indication the base oil is very different.
I'm no tribologist (nor do I pretend to be one by posting this list / comments) but less VI is usually better but better quality VI's is better then cheapass stuff.
That info one will never get from oil company's.

Note that "my" Helix Ultra X 0W-30 is the lowest in viscosity across the range on this list.
I can't wait to rack up some more km's to do a change and a UOA.

Have fun with the list.

 

i wish i can understand what all these means...

 

Thanks for the post Spitfire. Someday I'll stick my big toe in the water!

For Raisantos- if you look at the relative relationship of each column, the lower number means a thinner viscosity at that specific temp. You will then see why I'm a whimp. SAE viscosity rating on the bottle doesn't necessarily tell you the whole story. German Castrol 0W30 just as easily could have been labeled 10W30 or 5W40.

 

INDYMAC Posted on Nov 1 2007, 12:57 PM
Did you know that water (H2O) is 1 cSt @20C @ sea level?


Anyway..
I would like to add that VI is not a chemical.
VI or viscosity index is a number that indicates how much the oil changes when the temperatures drop (basically).
Wikipedia explains it a lot better.
The chemicals that make the oil behave like that are the VII, viscosity index improvers.
Some (most) base oils will get too thick when cold or too thin when warm so they need chemicals to alter their behaviour.
The "cheapass chemicals" I was talking about, are those VII.
A higher VI therefore doesn't mean the oil is not as good or may shear down or up.
There are lots and lots of different chemicals to do the job and some are (more expensive and) better for longer.

AEHaas's website about thin oil is here:
http://63.240.161.99/motoroil/index.html

The oil viscosity calculator is here:
Note: the calculator is not accurate at very low (-20 and below IIRC) temps.
JAVA needs to be installed too.
http://www.geocities.com/CapeCanaveral/3655/VI.html

Have fun

edit: typo

 

cliff notes version?

 

Thanks, Spitfire. That's great information.

That Helix Ultra has some great low-temp viscosity! I'm looking forward to seeing your UOA. It's on the bottom of the SAE 30 weight range, but if it doesn't thin out too much, it's awesome. If your numbers look good, I may switch from the Amsoil 0W-30 that I'm currently using.

Cliff notes comment: To be an XW-30 oil, it has to have a viscosity of between approximately 9.3 & 12.4 cSt. All oils are MUCH more viscous (thicker) when cold. Because it has higher viscosity when cold, lubrication is not optimized (spray jet pattern, preferential oil flow through largest oil ports, oil filter bypass, potentially reduced oil flow due to pressure relief valve, delayed oil pressure at startup, etc). The closer an oil is to operating temp viscosity, the better it can do its job as intended. Therefore, the lower the cold temp viscosity of an oil, the better.

 

Linked to the Oil Journals