Originally Posted by RDY4WAR
Originally Posted by MolaKule
Originally Posted by viscous
I recently read someone's concern that too much zinc could cause
corrosion in the engine and/or accelerate oil oxidation resulting in thickened oil. The oil in question is Schaeffer Supreme 9000 Full Synthetic Racing Oil 5W-50. Is this a valid concern?
It's not the zinc that causes corrosion, it's the high levels of ZDDP which is a tri-molecular ester that contains atoms of phosphorus, sulfur, and zinc. When moisture and high temps enter the picture, this molecule can degrade into acids which can eventually overcome the acid-fighting base chemicals.
Base Definition in Chemistry
Mola, in your expert opinion (or fact), do you believe the alkyl groups attached to the molecule have an effect on the acidity/corrosion? Speaking to emissions systems as well here as you hear/read about less damage to emissions systems using primary alkyl ZDDP even though the phosphorus and sulfur content of the additive is the same. This would lead me to believe that the characteristics of the alkyl groups has an effect on the corrosive properties of the additive and possibly the same would apply in the engine... or am I off-base there?
The ZDDP molecule is a Multi-Function compound to a. reduce wear and b. as a secondary anti-oxidant.
I think there are at least two issues here: 1. the dosage level of ZDDP with respect to the amount of available anti-oxidants and base elements to fight acids, 2. the
volativity of the ZDDP molecule.
If the dosage level of the ZDDP is greater than the available anti-oxidants and acid fighting base elements then the acids eventually win out. While the alkyl groups can certainly reduce or resist the ZDDP molecule's breakup into acids somewhat, their main goal is to reduce volativity.
High dosage levels of ZDDP in racing oils is usually associated with low levels of acid fighting base elements given to us by the detergent compounds which is why racing oils are to be changed after each race.
Medium levels of ZDDP are found in diesel oils but these oils are highly dosed with combinations of anti-oxidants and various combinations of detergent compounds to reduce acid buildup.
Lower levels of ZDDP are found in modern daily driver engine oils to reduce catalytic poisoning, but ZDDP is not the only Anti-wear compound available. Borates, polymer esters, and other specialty chemicals are also included to help reduce wear. Reduced volativity of the ZDDP molecule is very important here.
Consideration of application requires a balanced formulation to reduce wear while keeping acid buildup to a minimum over the life of the oil.
Definition of alkyl group for non-chemistry readers;
The alkyl group is a type of functional group that has a carbon and hydrogen atom present in its structure. The general formula for an alkyl group is CnH2n+1, where n represents a number or integer. A functional group is a group of atoms that are easily identified in a given compound.