UOAs: Thick oil and higher wear

[rimmer1]

In my humble opinion when we step back from elitism about oil -- bouquet, cost, nation of origin, what goes better with dark meat or white meat -- the real question is what will make my engine work better AND LAST LONGER.

When I discussed oil viscosity with my mechanic, who races 400hp Civics, he laughed and told me that he was able to limp his car through a season of racing with a main bearing going with Redline 60 weight oil. Normally, with 5W30, it would have blown in 5 minutes.

I've seen studies by Timken that show high rpms and high viscosity are the best thing for bearings.

When you blow your engine, what goes? The bearings.

I'll keep putting Amsoil 20W50 in my 180,000 mile Prelude (and 10W40 during the winter) until somebody proves to me that 5W30 will do a better job of keep my engine out of the scrap yard. I don't care if I get better MPG, or my oil consumption is high or lower (lower would be better though).

I've got the little engine that could and I'd like it to keep going for another 200,000 miles. The rest is BS.

Rimmer

 

[pscholte]

rimmer1,

I think we all understand the logic of what you are saying, that many come to this site just to get the bottom line answer to: "I have a 3.5L Turboschmaltz and my driving pattern is and my climate is...what oil and filter might be best for me?" or "Which prevents overall wear better, a 0W40 or a 20W50?" We owe it to them to give a straight, no nonsense answer, and we have a group which I think can do that very well. But there are also a number of oil aficionados here who enjoy the opportunity to try different oils because they like to, not because they need to, and they like to talk alot about the composition, shades, nuances, origins and yes, even the bouquet of those oils. That's fine too. Hopefully this site will serve both well.

 

[labman]

On a cold start, a heavier oil could cause more wear in 2 ways. One, much of the oil the pump is pumping is going back to the sump through the pump bypass instead of to the bearings. Two, more of the oil that is going to the bearings is going unfiltered through the filter bypass. So what little oil the bearings are getting on start up, is unfiltered. My owners' manual says 5W-30, and that is what I am running. It worked in my 92 Grand Am HO Quad 4 until I got tired of replacing sealed wheel bearings and ignition coils at 180K.

Note, Stokes law says particles will move through a liquid at a rate proportional to its viscosity. The Gardener Holt method of determining viscosity uses the time it takes for a bubble to rise through the liquid. So the heavier the oil, the longer a particle will stay in suspension.

 

[Dr. T]

It is a good postulation since the higher volatility of the thinner oils amounts to greater burnoff and probability of 1. wear particles going out the tailpipe or 2. wear particles being directly involved in formation of varnish and sludge either on moving parts, gaskets, rings, etc.. Whereas there is "less" top-up and cooking of the thicker oils resulting in greater suspension of particles. Can someone point out how you get greater wear with a higher film thickness and strength of oil?

That is why I think 1 single UOA on a particular oil doesn't mean much without subsequent UOA's with the same oil since each oil has different cleaning properties and requires at least 2-3 concurrent UOA's for comparison. Not a one-time singe trial of a particular oil or viscosity.

 

[pedaltothemetal]

I think you can only get so much iron in UOA cause the particles precipitate onto the bottom of
the oil pan and gets stuck on the magnetic drain plug, or sucked into the oil filter. I always find a fine grey iron powder on my magnetic drain plug.

Leo

 

[Shannow]

quote:

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Originally posted by labman:
Note, Stokes law says particles will move through a liquid at a rate proportional to its viscosity. The Gardener Holt method of determining viscosity uses the time it takes for a bubble to rise through the liquid. So the heavier the oil, the longer a particle will stay in suspension.

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'zackerly

 

[sprintman]

Meaning?????

 

[Shannow]

ummm, slang for exactly.

(was gonna post about Stokes when I got home, but labman got there first)

 

[Ray Garlington]

Jay:

quote:

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The wear metal particles that FTIR analysis measures are

MolaKule:

quote:

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It is the detergent-dispersant additive package that determines how much stuff will be held in suspension.

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OK. Given the above, that 1} the UOA's done with FTIR show wear particles
Here is the new version of the original question:

Assume oils of different viscosity {thin and thick} with the same effective dispersant package {thus suspending an equivalent distribution of wear particles actually present in the engine}. Also, assume our UOAs are accurate in showing the thicker oil shows more wear on the FTIR analysis. Does this mean more engine wear is actually occuring?

Is it possible that the thick oil naturally generates more wear particles of a smaller size <5um, while the thin oil is generating particles of a larger size which are not being measured?

 

[MolaKule]

"Assume oils of different viscosity {thin and thick} with the same effective dispersant package {thus suspending an equivalent distribution of wear particles actually present in the engine}. Also, assume our UOAs are accurate in showing the thicker oil shows more wear on the FTIR analysis. Does this mean more engine wear is actually occuring?"

Wow, some very good probing and deep questions.

If we assume the ferrous and non-ferrous "wear" particles have been "flushed-out," i.e., due to left-over machining and what not, yes, wear particles are showing up inthe oil solution after run-in.

"Is it possible that the thick oil naturally generates more wear particles of a smaller size
I don't think so. I cannot think of any mechanism whereby a clean oil would directly contribute to wear. If a thick oil doesn't get into the clearances soon enough after rotation starts of say, of a journal and sleeve bearing system, then wear would occur very quickly. So due to the viscosity of the oil being too great for the clearances, then the mechanism of localized oil starvation would occur, albeit momentarily.

 

[Ray Garlington]

MoleKule:

quote:

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I cannot think of any mechanism whereby a clean oil would directly contribute to wear.

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OK. Assume you have two moving metal surfaces riding on a layer of "thick" oil in between. Now assume you apply the exact amount of pressure necessary to force those two surfaces together so that just the peaks of the imperfections in the two surfaces grind together. These are the
Now replace the thick oil with "thin" oil. The same amount of force used above will cause larger particles to be ground off. These are the >5um particles.

 

[MolaKule]

Ray G,

I think I see where you're coming from.

I am not sure heavier loads will result in larger particles, just a larger "volume" of wear particles. Wear of bearing surfaces resulting from pure surface loads is measured in grams or mass, and shows up in the UOA's as a density of particles, or ppm.

If the surface asperities (the rough hills and valleys of the surface finish as seen under a microscope) are less than or equal to the thickness of the oil film, then wear should occur. The size of the wear particles will be on the order of the size of the asperities, or > 0.25 um.

Now for abrasive wear particle from sand or silicon, the particle wear size will be a function of the sizes of the grains of sand, or > 2.5 um.

I think there are two time frames that need to be examined here. The first is the no-to-slow rpm condition at startup, and then the conditions of idle to higher rpms and varying loads.

Less assume a journal is sitting in the bearing with no rotation and there is little or no oil film between the two. During the first few revolutions, there will be wear (assuming no boundary additive), and wear particle size is dependant upon the size of the asperities or the fineness of the bore finish. At this snapshot in time, no oil, high vis or low vis, is going to prevent a measure of wear, because the film is too thin to prevent the asperities from touching (again assuming no boundary additives). It is at this snapshot that boundary additives come into play, since we are in the boundary lubrication regime:
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=21;t=000027

In the second snapshot, and as the journal revs up to idle, the oil is sucked into ("flows into") the clearance by the dual action of the journal inertia and the viscosity of the oil. The journal is lifted away from the bearing surface and starts to ride on a film of fluid called the hydrodynamic fluid layer; the hydrodynamic lubrication regime.

The lower viscosity oil will enter the clearance(s) much earlier, since it is less resistive to flow, than would a higher viscosity oil, which is more resistive to flow.

Now at higher loads and moderate rpms, the thicker the oil film the greater the distance between the journal and bearing, so at medium to high loads, a thicker film is advantageous.

Now at higher rpm and moderate loads (such as cruise), the oil viscosity needs to be as low as possible to allow enough fluid flow for proper cooling, according to the Lasche-McKee equations.

This is why I believe the middle grade and range multi-viscosity oils provide the optimum viscosity range for starting and cruise, and why we see wear to be lower with these oils than the we do with the extreme viscosity range oils.

[ July 23, 2003, 03:15 PM: Message edited by: MolaKule ]

 

[Ray Garlington]

MolaKule,

Thanks for your detailed response, which is very helpful. I have not studied this before and appreciate the time & care you took in response.

So, it appears, we have on the one hand chemical/mechanical engineers who are quite confident that UOA numbers accurately reflect wear. I don't have much trouble throwing my hat into that ring.

On the other hand, we still have mechanics who are observing an unusual # of engine failures on some engines that use thin oil. I'll call your attention to Ingo Koth (www.motorrevision.de)

My European Internet buddies tell me he has extensive experience with BMW engines and his take is not to use sae10 oils on M40 engines unless there is a specific reason to do so. Also, he has a lot of statistics on the M20 engine, and recommends 15W-40 on it.
Ove Kvam (Norway) says: "Ingo reports that there is a correlation between thin oils and cracked heads. He reports that the thin oils drain out overnight. I don't think he is 100 percent sure about what causes all the cracked head on the cars belonging to customers that run thin synthetic longlife oils. He thinks it has to do with different vibrations.

He has also noticed that the life of the bearings between the crank and conrods is longer if you use a thicker oil. "

==============
I think the point that thin oils drain off overnight, but thicker oils stay behind might be worth pursuing. If the thin oil *does* drain off, while the thick oil stays in place, then the dynamics of engine wear on startup are a little different than you postulate.

 

[MolaKule]

"Now at higher rpm and moderate loads (such as cruise), the oil viscosity needs to be as low as possible to allow enough fluid flow for proper cooling, according to the Lasche-McKee equations."

The lowest viscosity "allowed" is determined by the clearances in the engine at operating temperature.

"I think the point that thin oils drain off overnight, but thicker oils stay behind might be worth pursuing. If the thin oil *does* drain off, while the thick oil stays in place, then the dynamics of engine wear on startup are a little different than you postulate."

What determines whether an oil will drain off or not is not determined by viscosity. Rather it is determined by an addtive in the oil:
1. Tackifier - the stickifier used mostly in gear lubes, way oils, and chain lubes.
2. Surfactant - spreads additives to surface pores of metals and can be sticky when cool. When hot, acts like host oil.

 

[Eiron]

quote:

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Originally posted by pscholte:
... "I have a 3.5L Turboschmaltz ..."

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Hey moribundman,
Do you think we could get Paul to help shoe-horn one of these engines into a Trabbi? Or a Metropolitan?

quote:

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Originally posted by Ray Garlington:
... "I don't think he is 100 percent sure about what causes all the cracked head on the cars belonging to customers that run thin synthetic longlife oils." ...

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Hi Ray, I've got some curiosity questions for you:
What constitutes his definition of "thin synthetic longlife oils"? Anything less than a 15W-40? Are there any long-life oils rated heavier than 10W-40? And is he only concerned with the xW- end of the vis? Oh, & what intervals does he recommend?

 

[moribundman]

quote:

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Hey moribundman,
Do you think we could get Paul to help shoe-horn one of these engines into a Trabbi? Or a Metropolitan?

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Eiron, I think the 3.5L Turboschmaltz might be just the right motor for a Nash. BEEP! BEEP!

[ July 23, 2003, 06:38 PM: Message edited by: moribundman ]

 

[Ray Garlington]

Eiron:

quote:

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What constitutes his definition of "thin synthetic longlife oils"? Anything less than a 15W-40? Are there any long-life oils rated heavier than 10W-40? And is he only concerned with the xW- end of the vis? Oh, & what intervals does he recommend?

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I don't read German, so here are my impressions from 3rd hand info: His database is quite large and his experience on BMW engines is extensive. He is a well-respected mechanic. He doesn't like 0w--anything. Probably 5w-anything is suspect. He'd probably go for a 10w-60, and of course the 15w-40, 15w-50 .. I'll guess that all the synthetic oils are considered 'long life' in Europe (A3-A5 spec). Never heard anything about what he recommends for oil-change intervals.