just in case anybody was interested. i have highlighted 5w-20 vs 20w-50

11/11/2008 9:38:22 AM

http://obamasrebuttal.ytmnd.com/

11/11/2008 10:08:37 AM

What I'd like to know about oils is this: how to maintain a high compressive film strength while reducing lateral shear to a minimum?

who the hell here can tell me more about oil chemistries. I mean, GET IN DEPTH on it. And I'll try to follow.

Actually, as it appears, if tolerances are maintained and the oiling system can provide enough pressure, then it makes sense to use the thinnest oil possible...IF you can guarantee that radial shear and oil film displacement won't be compromised to the point of metal-to-metal contact.

I've also learned that an oiling system's efficiency has a LOT to do with strategic placement of galleries and journal ports and the hydraulic advantage exhibited therein. Of course, centrifugal forces come into play as well.

Pressurized sleeve bearings, I think, have the potential to provide unparalleled performance, as opposed to ball, roller, or needle bearings. And much of that has to do with the distribution of bearing load over a continuous film...a large surface area over which to dissipate load. I think, for this reason, they are much more suited to the internals of a reciprocating internal combustion engine than, say, ball or roller bearings. The oil film helps to dampen impulses and there are no point impulse or compressive loads on the journals or races. the catch here is viscosity...fluid shear. Unfavorable normal to the bearing surface, highly favorable annular or tangential to the bearing surface.

11/11/2008 5:01:53 PM

You should of had to sit through the lubrication part of our precision maintenance class, our Mobil rep is a lube geek.

Viscosity isn't everything, the bases the oil are derived from affect shear, presuure, breakdown and operating temps, ability to tolerate water and particulate contamination, anti corrosion properties, and property chages over the life of the oil.

Considering we have several lube systems that operate on 5000-10000gal, and never get changed, just filtered, topped off, and dewatered, that stuff is kinda important.

11/11/2008 6:05:45 PM

the only [piston gas engine] applications where I can see very high viscosity oil being advantageous are those motors that are prone to bearing problems. The Mark III Supra 7M motors come to mind, and the turbo 3000GT motors (especially the 91-93 motors). In those cases the added protection is worth the frictional losses.

11/11/2008 6:56:15 PM

Quote :

"Viscosity isn't everything, the bases the oil are derived from affect shear, presuure, breakdown and operating temps, ability to tolerate water and particulate contamination, anti corrosion properties, and property chages over the life of the oil."

I agree that viscosity ain't everything, especially on the big stuff where sheer mass dampens out a lot of impulse loading, and clearances are usually larger, allowing for a higher total rate of shear. Don't forget that bearing areas are much larger, rpm's are much lower, and operation is much more steady state. AND...friction losses due to oil shear are proportionately much less of a concern.

In a car engine...throw a lot of that right out the window. Higher rpms, concerns with harmonic vibration and damping same, continuous contamination by combustion deposits, highly cyclic operation, often under extreme load, and frequent condensation in the oil from many heat/cooling cycles. Herein lies the importance of detergents, dispersants, extreme pressure additives such as zinc dialkyldithiophosphate, and the oil's effective total base number.

But I think that choice in base stocks, wetting agents, and viscosity can go a loooong way to increasing an engine's efficiency and longevity. Big catch is, on a per-unit basis, it's just not economically worth it for the auto makers to install microparticulate filtration and oil conditioning systems or engineer an engine with a much more complicated high-pressure, low volume oiling system and the corresponding journal, positive seal, and variable bleed port, etc. As a side benefit, crankcase windage could also be greatly reduced. And the engine could likely run on very light oil.

Interesting to note: Dad was in the Coast Guard, aboard three different ships. One of them, the Westwind (oh, about 250' long and tubby; did 15 knots tops), had six Fairbanks-Morse opposed-piston diesels. Low speed engines...and they used SAE 30 for lubricating oil.

11/11/2008 7:18:14 PM

bearings are larger yes, but we still have 24"+ tapered roller bearings turning in excess of 3600 rpm

and at least 20-4" sleeve bearings turning 10k rpm on our turbines

11/11/2008 7:31:44 PM

http://www.bobistheoilguy.com/

11/11/2008 7:38:46 PM

Quote :

"Considering we have several lube systems that operate on 5000-10000gal, and never get changed, just filtered, topped off, and dewatered, that stuff is kinda important."

is never here really never or some absurd length of time (10s of years or longer)

11/12/2008 10:01:18 AM

never, with the filtration, dryers, and testing we do, there is no need, hell we even have a "kidney" we can hook into a system if he tests come out bad

11/12/2008 4:59:19 PM

it seems like it's cool to take pride in rarely/almost never changing your oil these days

11/13/2008 12:54:37 AM

^ yeah really, what the fuck is the deal with that? regardless if the oil can last longer, the 3000 mile interval has a huge benefit- keeping people on top of maintenance. this is very important these days as more and more auto companies are pushing their vehicles as super reliable and offering 100k mile warranties to lull consumers into a false sense of security.

11/13/2008 2:47:50 AM

with only reading like 1/3 of optmusprimes post i can tell he lost that post...my honda(rip) was ever 7500 miles...he was saying like ever 3k or something...anyhow...change it ever 5k...the end

[Edited on November 13, 2008 at 3:40 AM. Reason : god dammit i got a feeling he was "right" anyway...god i hate him...his whore wanted to fuck...]

11/13/2008 3:39:42 AM