Having educated myself a bit more on the details of positive displacement pumps, it’s pretty obvious. With a PD pump, there’s never a fluid connection between the low and high pressure sides, so additional hydrostatic pressure on the inlet side can’t be transmitted through to the outlet. On, say, a centrifugal pump, it can.
Thinking about it a little more, even if the additional hydrostatic pressure did get carried through, I doubt it would matter much. Oil’s density is, what, about 6 pounds/gallon? Hydrostatic pressure in a liquid is densitygravitydepth, so the pressure increase from high oil levels would be:
(6 lbm/gal) * (9.81 m/s[sup]2[/sup]) = something in horrid units, which I can convert on my calculator to: 2.6x10[sup]-2[/sup] psi/inch.
An oil pan filled 1 foot too deep would have a pressure at the inlet only 0.3 psi higher than normal. I can’t believe that this would be enough to damage anything in the first place.
So, yeah, the high-oil-pressure notion seems like bunk, for more than one reason.
Common sense would seem to concluded that, all else being equal, thinner oil will burn away faster than thicker oil. But I’ve heard this is not true from a certain “industry experts.” In fact, one claims that using thicker oil will actually increase oil consumption. Wish I could find the straight dope on this…
The API service category SH oil designation was made obsolete in 1996. If you see a bottle that has “SH” as its highest rating, it could be from a back-stock of oil, and could be pretty old.
Yeah, I apologize for throwing that out in the first place. It was the way I learned it, but apparently I was taught wrong. Oh well, sometimes fighting your own ignorance means that you have to unlearn something. Thanks all.
Fair enough. I pulled 6 lbm/gal out of my head, without bothering to look it up. About the only number I can ever remember is the density of water, which is approximately 8 lbm/gal. Knew oil was somewhat less, but was feeling lazy.
0.03 lbm/in[sup]3[/sup] is about 6.93 lbm/gal. What’s 15% among friends?
English units are evil, I agree. Unfortunately, the rule-of-thumb values that I can recall are often in that system. Bummer…
As far as performance improvement of SH versus SJ, I doubt that there is any measureable difference to anyone.
IIRC, oil can “expire”, but I have never seen an actual date. I do know that some of the additives will break down over time, and I have verified that 12-year old oil, still in it’s sealed, airtight plastic container can develop a significant, disturbing fractionalization (I saw this in two quarts I examined in an old garage). So…to be safe, I would not use old oil myself.
If it was 5 years or under…it likely is not bad. Ten years? Who knows…but then again, I’m one of those people who “wastes their money” by using full synthetic oil for my 3000-mile changes…
I pulled 6 lbm/gal out of my head, without bothering to look it up. About the only number I can ever remember is the density of water, which is approximately 8 lbm/gal. Knew oil was somewhat less, but was feeling lazy.