Are all 75W-90 gear oils synthetic?

[MolaKule]

Sorry about the link guys, the "create link" option must have truncated it.

Here it is:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=729289#Post729289

 

[MolaKule]

Quote:
Do these VII provide the same film continuity as the base oil?


The VII's thicken up the oil at high temperatures to insure the oil film remains thick enough for lubrication.

 

[PandaBear]

If you want the absolute thinnest 75w90, why not try the 75w85 from Toyota or Redline?

 

[donnyj08]

my autozone has conventional valvoline 75w90 it comes in a white bottle just like valvoline's conventional engine oils.

the durablend 75w90 is in a blue bottle just like durablend motor oil.

and synpower 75w90 is in a silver bottle just like synpower motor oils.

 

[Tempest]

Originally Posted By: MolaKule
Quote:
Do these VII provide the same film continuity as the base oil?


The VII's thicken up the oil at high temperatures to insure the oil film remains thick enough for lubrication.


As run through a viscometer, sure. To the best of my understanding, VII will not provide the same "film strength" as a base oil does under actual load.

Isn't that why HTHS was established for engine oils?

 

[Tempest]

Originally Posted By: Quattro Pete
Originally Posted By: Tempest
A conventional 75W90 will have a good amount of VII

75w-90 gear oil is equivalent to something like 15w-40 engine oil when it comes to viscosity. If they can make a shear stable 15w-40 mineral oil (think most HDEOs), then they should be able to make a shear stable 75w-90 mineral gear oil, too.

Be aware that the shearing forces in gears are far higher than in engines. Note that gear oils use extreme pressure additives for a reason, and that they are absent in motor oil.

Gears operate in boundary and mixed regimes far more than do engines. The VII in motor oil is also different from those used in gear oils.

 

[Tempest]

Quote:
A lubricating oil has been generally incorporated with a viscosity- index improver to secure a certain viscosity at high temperature. However, a viscosity index improver involves a problem that it cannot secure an oil film thicker than expected, because a high"m,olecular-weight polymer as a viscosity index improver component tends to be oriented under high shear stress conditions.

http://www.google.com/patents/EP1920035A1?cl=en

Now that patent application (from 2008) is all about getting around that with their new chemistry so maybe things have changed, but VII of the past (all else equal) will not provide the same hydrodynamic protection as a gear oil without.

 

[MolaKule]

The original OP's question was:

Quote:
Are there any conventional 75W-90 gear oils, or are all synthetic? (I think so, but I'm not sure.)


I think this discussion has replied in the affirmative. (Scenes of "Tackleberry" in Police Academy).

I would suggest that a new topic be started discussing VII's and HTHS. Somewhere in BITOG (maybe the Science and Technology of Oils and Lubricant Additives) there is a topic on HTHS that can be revived.

 

[Tempest]

Quote:
I think this discussion has replied in the affirmative. (Scenes of "Tackleberry" in Police Academy).

He did ask about the higher end gears oils as well so I was just trying to explain my first comment in the thread.

 

[artificialist]

Originally Posted By: donnyj08

and synpower 75w90 is in a silver bottle just like synpower motor oils.

Also, older synpower gear oil and engine oil came in copper colored bottles. Since gear oil isn't as fast selling as engine oil, it is very common to see some gold bottle Synpower gear oil.