Deposits, Sludge and Base Oils

[Hirev]

So I have seen good UOA up to 7500 miles on Group II base oils. But do or can UOA tell you anything about deposits or sludge?

Is it right to assume in general, the higher the Base oil number is the less deposits and sludge will be over the long run?

 

[moribundman]

All I can say is that my engine did not suffer from deposits or sludge after running a good Group III oil for 100k miles.

 

[pitzel]

TBN is merely a measure of an oil's ability to neutralize and/or buffering capability insofar as it relates to combustion gasses. Obviously you would not want highly acidic oil circulating in your crankcase, eating away your metallic parts and gaskets.

Sludge is invariably caused by localized thermal breakdown of oil, due to factors including localized heating, poor circulation of oil, overly 'thick' oil, and oil with an inadequate flashpoint for the particular application.

For example, sludge buildup is seen when oil that has experienced drastic viscosity thickening is run. The reasons for the sludge buildup are as follows:

a) The 'thick' oil doesn't cool the engine effectively, so the engine runs hotter. Thick oil also can't be pumped through the engine at nearly the same rate as thinner oil can.

b) The hotter running engine therefore experiences higher surface temperatures internally, which in turn, causes some poorly circulated oil to be overheated.

c) The overheated oil forms as sludge on the innards of the engine and in the oil, further thickening the oil, further making the problem in a) worse, and the cycle repeats.

Reciprocating engine oil is unique in that it is formulated to be extremely basic, as compared to turbine oils that do not need to be formulated with basic neutralizers. Turbine oils and gear oils therefore will have fairly low TBN's as they are not exposed to combustion gases.

To answer the original questions:

1) Yes, a used oil analysis will measure viscosity thickening. If the oil has thickened to a high degree, ie: a 5W30 thickens into a 20W50 grade, it is likely that some sludge formation has occurred.

2) TBN is generally represented in terms of a sodium hydroxide (NaOH) titration equivilant. Sodium hydroxide, or bases in general, are generally good dissolvers of organic material, such as sludge, while acids are good dissolvers of metallic components. A weak TBN not only shows that the oil has been depleted through combustion gas acid loading, but also shows depletion due to reaction with carbon-laden deposits or thermal breakdown products of oil itself.

 

[Dr. T]

Yeah, well all pen-on-paper theories aside, I will postulate that an oil that stays on the surface (as opposed to cooking/vaporizing and leaving sludge behind) will provide a i) better net cooling ii) a cleaner engine iii) improved engine efficiency thru improved compression and piston sealing iv) longer-lasting oil. Hence, consumption can be viewed as a downward spiral.

Previous board member and engine-man 'Jerry' told us of many instances of engines with good used oil analysis but were carboned-up on engine disassembly. So, I'm not so sure how/if a used oil analysis can show you the engine cleanliness condition. This has always been my question too.

 

[buster]

http://www.practicingoilanalysis.co...eid=714&relatedbookgroup=ContaminationControl

quote:

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Degradation of the Fluid Base Stock
Oxidation: A primary chemical degradation process in many applications is the oxidation of the fluid’s base stock. The oxidation process proceeds through a series of chemical chain reactions and is self-propagating, with the intermediate, reactive chemical species regenerating themselves during the process. The process results in the conversion of the fluid base stock to oxygenated compounds, such as organic acids in the case of hydrocarbon or poly-ol ester based base stocks, and eventually, high molecular weight polymeric compounds. The polymeric compounds are often insoluble and settle out of the fluid as gums, resins or sludges.

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quote:

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Hydrolysis: Fluid base stocks that are comprised of ester compounds, such as polyol ester gas turbine lubricants and phosphate ester hydraulic fluids, can undergo hydrolysis in the presence of free water under operating conditions in the system. This results in the formation of acidic compounds that can react with the materials of the system components and hence, corrode the components.

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WE can compare wear metals all day long, but to me, these two issues above are much more critical in maintaining a healthy engine.

[ April 27, 2005, 10:29 PM: Message edited by: buster ]

 

[Geoff]

Group III oils are very clean from my research. They are nearly or are as pure (depending on what you read) as PAO oils. The problem of the waxy particles (very high in Pennsylvania crude oil that at one point was what Castrol, Valvoline, Quaker State and Pennzoil used) in mineral oil is gone. I think this is true for Group II oils as well eg Chevron ISO-Syn.

The big sludge producers are impure Group I base oils, combustion byproducts not purged by a good PCV system, dirt, poor oil circulation, leaking head gaskets, leaking rings (poor compression), broken down viscosity improvers, and worn out oil that can't keep the bad stuff suspended.

Since most engines run around boiling temp (212F/100C) for clean burning, the hot environment exacerbates volatility, catalyzes the buildup of sludge, and leaves residues.

So

Experts please expand....

 

[buster]

What about the additives? Do they play as big of a role in preventing deposits as do the baseoils?

 

[MGBV8]

Hi Buster
Off topic but I assume you are referring to RL

http://www.noria.com/learning_center/category_article.asp?articleid=646&relatedbookgroup=OilAnalysis

Not sure how the "ester" in GC would compare to RL re sludge

 

[buster]

Thanks for the link. I was more interested in knowing how the Group II+ SM oils are at preventing deposits.

 

[bruce381]

quote:

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Originally posted by buster:
What about the additives? Do they play as big of a role in preventing deposits as do the baseoils?

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Additives do play a far more important role in
deposits than base oil. A un additized PAO will sludge big time but with the right additive (anti oxidant) it will run a long time very additive dependant.
bruce

 

[JAG]

When exposed to very high temps outside of an engine, I've seen virgin Valvoline 5W-40 and Mobil 1 0W-40 not only sludge but also leave behind "fly-crap-like" circular, raised deposits. Conclude what you can from that. It's hard for me though, because I don't know if the sludge and deposits were from possibly Group 1 basestock additive carrier or from the primary basestocks of the oil. Last I heard M1 uses an ester carrier oil and if so, that means their primary basestocks (>=Group 4) can leave behind sludge and deposits simply from heat alone (no engine acids or moisture to worsen it). Of note, I was not able to cause Amsoil 5W-40 or Redline 10w30 to create the mysterious fly-crap-like deposits.

 

[BigAl]

quote:

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Originally posted by buster:
What about the additives? Do they play as big of a role in preventing deposits as do the baseoils?

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The detergent/dispersant additives play a major role in sludge prevention. As long as they are still functional, much of the sludge forming material (oxidized oil, carbon, etc.) stays suspended, and the larger particles get carried to the oil filter. When these additives are exhausted, this material falls out of suspension to form sludge.

 

[Blue99]

Sludge is technically a combination of combustion by-products and moisture produced within the temperature extremes of an engine environment.

I don't think these fly specs are evidence of sludge, but possibly a chemical reaction of the additives with the container that the oil is being heated in.

 

[rg144]

quote:

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Originally posted by Hirev:
So I have seen good UOA up to 7500 miles on Group II base oils. But do or can UOA tell you anything about deposits or sludge?

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Noria Learning Center answers that exact question: Using Oil Analysis to Control Varnish and Sludge

 

[Blue99]

Here's an article in Lube Report with pictures of sludge generated by running a non-detergent API SA oil in the Sequence VG sludge & deposit test.

This test is 216 hrs in length, intentionally run with fuel blowby and varying engine oil temp cycles from 120F to 210F.

Note that the test was halted after only 168 hrs for the SA oil, which lacks the necessary anti-oxidants and detergents/dispersants to fight the sludge generating elements.

 

[JAG]

Definition of sludge aside, virgin oil can leave a sludge-like layer (certainly is an oxidation layer) without any combustion by-products or moisture. It doesn't really matter what terms we call these things because they are what they are. I'm not at all disagreeing with what you said about sludge/combustion by-products/moisture, just adding what I've found in testing that is done for scientific curiosity reasons mostly.

I think those deposits are impurities in the basestocks aggregating and bonding with the metal cups, but I can't prove it yet. I did test a Group 1 basestock SH or SJ (can't recall) SAE 30 Pennzoil oil and you would not believe the amount of crap that it deposited on the cup! It was atrocious. That is what I'm basing above belief on.

But I must add a caveat, these were temps well above those seen in an engine. I was just having fun experimenting.

 

[JAG]

Nice Lube Report link! I posted above before I saw it. Begs the question of how much was due to basestocks and how much to additive package. I bet both played a role.