why not two oils?

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Jan 29, 2006
It seems that the demands on oil really depend on which area of lubrication one is discussing. So, why don't engineers isolate the lubricant between different areas. For example, why don't we have one fluid circuit for the crank and rings and a different circuit for the cam. Then, we can have two lubricants with taylored characteristics for the two different applications. It seems that this would not be different than current isolation of transmission fluids from engine oil. Am I missing something here?
Interesting thought, with the valvetrain having a heavier weight than the crankcase? Is this prior to the shift to roller cam followers? I would have to agree with Pablo thought - need another filter, pump (power/efficiency penalty), more weight, engine is less compact, etc. I believe the subtle design alterations made in more recent valvetrain designs allows for similar and maybe even greater wear protection than previous, while selecting oils for general use of lower viscosities overall. I don't think this shift is because of one thing and only one thing - just think of how the lubricant industry has had to evolve to produce lighter and yet less volital oil, and that which is more stable over similar or extended OCI's at agreeable costs at mass market volumes, etc. In some sense, things just seem to be coming together behind the idea of greater overall operating efficiency. Sorry, got carried away there. [Big Grin]
It's a neat observation, but we oil nuts are the exception, not the rule. Joe Consumer would not buy a car that required 2 motor oils.
and can you imagine the mistakes that would be made at the local quick stops?
the big marine diesels do just that. A crank lube, and a hjgh TBN piston/ring lube. But they are BIG
Originally posted by simple_gifts: For a car not sure what problem this would be solving....
Yeah, but you have to hand it to the guy for comming up with an original question. [Smile]
Sorry for not responding sooner, I have been away. simple_gifts, The problem is that the ideal lubricant for different parts is different. Each area zone of lubrication could use a different lube. Pablo, Curious Kid, Total pumped fluid may not have to change, so load on the engine may or may not increase. As for extra parts, I think that an entire oil pump does not come close to the number of parts in modern lifters. mikemc, My crystal ball is not as efficient as yours. I have no way to know if one additional fluid under the hood would affect the average vehicle consumer. They did not quit buying vehicles when the hydraulic clutch was added with its additional fluid -nor power steering, nor other fluids. I don't think that the average consumer knows what's under the hood. So, I don't see an added fluid as some sort of marketing obstacle. In addition, since one could isolate the new lubicant circuits from combustion gasses, the new lubricant would not need to be changed as often.
Quote: "It's a neat observation, but we oil nuts are the exception, not the rule. Joe Consumer would not buy a car that required 2 motor oils. " I would... The oil pump would be designed with two isolated housings, with a common drive. The cam lubricant would be isolated from the crank lube, and would not pick up fuel soot, so a small filter for metal particles (im thinking magnet here)would pretty much be all that's required. I think the lube would last a long time if not contaminated, and only require a change every so often. I would buy off on that in a heartbeat.
Rotaries? Thought the "valve gear" in the Wankel was a la 2-stroke: ports in the outer walls of the chamber, therefore no camshaft required. Unless you mean rotary as in the Gnome WW1 period. One valve in the head, one in the piston, originally. Lube was constant loss.
GMorg, I thought of that, too, the other day. Yes, comnplexity, cost wins in this case, and we don't do 2 oils. I thought of it when I was thinking I don't mind a 0w-20 in my crankshaft bearing, but the cam surfaces could use a heavier 50 weight oil. Remember the crank bearings are enclosed, and the cam surfaces are more open, not trapping the lube in their as well.
It can of course be done. Engineers don't design auto engines with this feature because it is absolutely not needed. Nothing would be solved , but complexity and costs would sure increase.
Isn't the problem just that with each new "higher" (higher letter, not higher quality) API oil grade since SG, that the oils just keep getting wimpier and wimpier??? To protect the emissions systems, add packs aren't what they use to be. Back when oils had a descent add pack, cams were a lot happer! So how about some new emissions reducing technology that would allow us oils with awsome add packs??? In most dirt bikes (except the newer Honda 250/450's) the engine/transmission oil is integrated. In order to withstand the thrashing that meshing gears dish out, motorcycle oil has to have lots of high pressure additives. This is just makes things all the better for the bikes cam!
you'd be adding some weight. the seperate pump mechanisms and tanks for the various lube areas. besides that, when is the last time your average car wiped out the cam because the oil wasn't good enough?
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