Do additives deplete?

[The_Oz]

Additives such as Barium, Magnesium, Zinc, Phosphor, Sodium, and Calcium. Do they deplete during the course of the oil's life inside the engine? I was perusing through Petro Canada's Oil Handbook when they state that the additives mentioned above do not deplete. I find this odd since an AW like Zinc or Moly should plate itself on metallic surfaces and stay there. Isn't that what these additives suppose to do? Also, Calcium is suppose to "clean" the engine, therefore it should also diminish. What am I missing here? Oz

 

[MolaKule]

Well, let's see. The ORIGINAL Magnesium and calcium do deplete when they are consumed by attacking the acids in the oil. Zinc does get sheared off the surfaces (as well as Moly, etc) somewhat and has to be replenished, and may be reacted. ZDDP is also an anti-oxidant and anti-corrosive additive, so it becomes depleted through three different mechanisms. Many of the additives are transformed to other forms of the same element.

 

[The_Oz]

So MolaKule, If we take Havoline Synthetic 5W40 which has 2100ppm of Zinc, does it mean I will have 2100ppm of some-type of Zinc (not original Zinc) after 3000miles/5000kms? Regards, Oz

 

[Jay]

I've read that pour-point depressants in conventional oils are depleted by cold temperatures.

 

[MolaKule]

OZ, "If we take Havoline Synthetic 5W40 which has 2100ppm of Zinc, does it mean I will have 2100ppm of some-type of Zinc (not original Zinc) after 3000miles/5000kms? Let's say the virign oil has 2,100 ppm of Zinc Diaryldithiophosphate or Diakyldithiophosphate. I.E., ZDDP is an ester of zinc, sulfur, and phosphorous added to the oil. Minus the evaporation of a small fraction of the ZDDP and plating, you might have say 1,895 ppm of zinc at 3k miles. Now if you extend the oil past 3k, the ZDDP starts breaking-up into its separate components so it's effectiveness is reduced, because it need the sulfur atoms to help the zinc bond to the metal. So you will have zinc in the oil, but the zinc cannot rebond to the metal as it did before. When you add oil, additive replenishment takes place and replaces the bonded zinc, phosphorous, and sulfur atoms, so they can once again attach themselves to the metal. In additive chemistry, we say that ZDDP is a polar ester, because polar generally means it has an ionic affinity to metal. Charges of different signs (+, -) attract each other.

 

[widman]

MolaKule - love your posts. Thanks.....Good to know the reasons why I see the depletion in analysis.

 

[MolaKule]

Thanks, As an FYI, there are newer and more advanced anti-wear agents as well, other than ZDDP: 1. ZDTP (zinc bis[O,O diisopropyldithiophosphate], a longer lasting version of ZDDP, 2. phosphosulferized acrylates 3. a class called "Alkyamino Diisoamylphosprodithioates The last AW additive has been found to reduce wear scar diameters by 45%.

 

[dave in MD]

"So you will have zinc in the oil, but the zinc cannot rebond to the metal as it did before." Molakule, Do I understand this correctly? Using your example say you have the oil analyzed at this point you will still read 1,895 ppm of zinc, even though the zinc compounds cannot bond to the metal?

 

[TooSlick]

Dave, You really can't use additive levels in used oil analysis to tell how much life the oil has left. These additives will show up even after they have become inactive from performing their functions. If you want to look at how much detergent/dispersant is left, compare the TBN to the baseline value. Since ZDDP also prevents oxidation, you can get a very rough feel for how much is left by looking at the percentage of oxidation of the basestock. Generally what you focus on in spectrographic analysis are contamination levels, viscosity, total solids and degradation of the baseoil (oxidation/nitration/TBN depletion). TooSlick

 

[MolaKule]

Dave in Maryland, That's correct. TooSlick is correct except that the Mag and Calcium levels (detergent/Dispersants) can also indicate oil degradation. As TS said, "Generally what you focus on in spectrographic analysis are contamination levels, viscosity, total solids and degradation of the baseoil (oxidation/nitration/TBN depletion)." The levels of metallics in a used oil analysis from metallic AW and FM additives cannot always be used as an indication of continued effectiveness. The major exception is Moly and Antimony. If you see lower levels of Moly and/or Antimony in UOA (as compared to a clean oil analysis), this usually indicates that these metal sulfonates have been "uptaken" and have coated engine internals.