Zuki-Ron said:
As far as fluid types, I just coped what was in the manual, and though I used my own language for their cautions, that is what was printed.
Sure Automatics have a circulation system and the bearings the drum gear rides on are presurized, but the gear sets are all splash oiled from overspray. Same thing with the Transfer cases. The main bearings are pressurized and everything else is splash oiled.
I was sure I heard somewhere that ATF was OK'd for use in AX-5 transmissions, or maybe it was 30W. However, what is in the book is gold to me.
You have to get away from this "sticktation" idea you have. It's all about viscosity. If you have two surfaces that you want to lubricate, you need to provide separation. A high volume of a low viscosity fluid, is a good sub for a high viscosity-low volume fluid if you can do it. The problem with unsubmerged gears, like an axle, is that there is no way to contain the surface like there is a surface bearing and you can't build pressure, so that's why they chose a high viscosity fluid, not "sticktation".
AX-5 gear cases are pretty much submerged in fluid, so I would think that ATF or atleast a lower viscosity fluid would be OK.
Honda has been using 30W oil in transaxle cases since their 1200 Civic day without a problem. Imersion, tighter clearances, and not loading the transaxle directly allows them to run a lower viscosity fliud and not have wear related failures.
I vaguely remember that about Honda - my 1980 Accord ran the same oil in the transaxle as it did in the engine (kept logistics simple, again. I like that...)
Most autos I've torn down have bushings or oil-film bearings for the shafts (like in your engine,) and Torrington thrust bearings for in between (flat rollers arranged in a circle, so that parts don't have to rub against each other.) Torringtons don't tend to require a great deal of lubrication, so they're covered by oil splashing around anyhow.
I can see where some confusion is arising - as I use it WRT oils, "stiction" refers to the surface adhesion of the oil. When you have a dip/splash lubed system (typical manual transmission or drive axle,) lubrication to the entire assembly is essentially provided by the portion that dips down into the lubricant, and the lubricant is then carried up into the rest of the train. "Stiction." Surface adhesion.
It doesn't have much to do with viscosity - it's more to do with surface tension than anything else. The additive that sees to that is a sort of "reverse surfactant" - I don't know what it would be called, but it actually
increases surface tension a bit, rather than decreasing it (as a contrast, soap is technicall a "surfactant." It works to make water "wetter" - breaking down surface tension, so that it gets into/around/under more. It's not the soap that removes dirt from your hands - unless it has pumice in it. It's the fact that the water is able to get into more. Gear oil has an additive that does much the same thing in reverse - and engine oil and ATF has the same additive, only to a lesser degree. It's not as necessary when you have a circulating pump.) If you want more lubrication in a "dip/splash" setup, you either increase the fill level (meaning that the distance the lube has to travel "up" is reduced,) or you lower the assembly (same net effect.)
Does gear oil stick to surfaces more than engine oil or transmission fluid? I had a half-full 5 gallon bucket of gear oil upend itself in a work truck once upon a time, and it took me the best part of a month of cleaning at the end of the day to get it out enough to cut the smell down. Had a case of engine oil get caught under the generator when it fell, and I had
that hosed out inside of a week. Something is added to gear oil to make it sticky, let me tell you!
Viscosity is largely controlled by the base oil - gear oil comes from a "lower fraction" than engine oil or ATF. When crude oil is run through a cracking tower during refining, fractions can be anything from asphalt to kerosene, and there are a couple of gaseous fractions and a couple called "distillates" that are used as solvents (petroleum distillates are the most common.) Crude is "flashed" into a vapour at high temperatures, fed into the bottom of the tower, and then the various fractions separate/condense out at various levels - with lighter fractions going to higher levels in the tower. It's a fractional distillation process. Gasoline and Diesel, natch, are fractions as well - with Diesel being a "lower/heavier" fraction than gasoline.
Viscosity is largely controlled by base stock, and then modified by the use of long-chain temperature-sensitive polymer additives. Surface action is also controlled by additives - sometimes surfactants are added (intentionally or no. Most detergents added to engine oils and transmission fluids are also surfactants,) sometimes straight viscosity improvers are added, sometimes surface action improvers are added (makes the oil "stickier" than it would normally be, counters the action of surfactants, or whatever,) and any of a number of other things as well. Granted, I only took one semester of O Chem back in 1987, and what I know of petrochemistry comes from research and learning that way, so it's entirely possible I could have something mixed up. However, that's how I've been given to understand it.
Viscosity is what builds the cushion between moving parts, I'll not argue that at all. But, aren't the properties of lubricating oils myriad in number, and compromises to be made? Petrochemists make those compromises in a technical sense all of the time - for me, I have to make compromises in language, since I don't know the words that are supposed to be used to describe what I'm talking about... So, I'm always willing to be corrected - but it does take some doing to prove that I'm wrong. It is possible...