The Mandatory Viscosity

[coffee]

I just wondered if there were gas only oils in the 15w40 range, not a big deal really. Thanks for the input.

 

[Dyoel182]

Not in that exact range since thats the HDEO diesel/gas oil spec. If you look on the back of the bottle it should say SL/SM which is the same gas spec the other weights should have.

 

[Forest]

That was an interesting article and makes a person think...hmm, now do I start using a 15w40?

Good grief Coffee! Not again.....use Pennzoil 10w-30 HM! LOL ;-)

 

[coffee]

hehe, I know but I am trying to research all my options this time before committing to buying one.

 

[TurboJim]

"Thinner oils have less drag, and therefore less friction and wear. Right? Perhaps in the test engine or engines that experience normal operation. But somewhat thicker oils may offer more protection for more severe operations such as driving through mountains, pulling a boat, dusty conditions, short trips, high rpm, overloading, overheating and overcooling."

Short trips? Overcooling? How so?

 

[RI_RS4]

Originally Posted By: TurboJim
"Thinner oils have less drag, and therefore less friction and wear. Right?



Drag, friction and wear do not have a 1:1 correspondence. Thinner oils do have less viscosity drag or windage loss, but they do not necessarily have less friction and wear.

 

[Curious Kid]

IIRC, mixed film lubrication regimen provides for the most efficient operation, and that's where base oil AND additives need to work in synch to keep thing from getting out of hand - increase viscosity/reducing load/increasing motion merely shifts the regimen towards a more hydrodynamic state that provides an increased fluid buffer but reduces efficiency through pumping/shearing losses, while running thinner viscosities/increasing load/slowing speeds shifts the lubrication regimen towards increasing additive dependence (towards boundry phase), where efficiency quickly begins to diminish.

 

[JAG]

Stribeck Curves.
http://www.sae.org/events/pfs/presentations/2005spikes.pdf

 

[Curious Kid]

Thank you JAG for the link! Very interesting, including the effects of ZDDP - it concentrations in the base oil and effects on wear, as well as how it contributes to surface plan irregularities.

From the above link, it would appear that the most efficient lubrication phase from the standpoint of minimizing energy losses between the lubricated assemblies, is shared between the hydrodynamic and mixed film regimens, rather than within the mixed film regimen alone as I attempted to recall from my previous readings.

Thanks again.
Happy Holidays!