Too Much Zinc = Corrosion?

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I recently read someone's concern that too much zinc could cause <span style="font-weight: bold">corrosion</span> 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?
 
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Originally Posted by ka9mnx
o answer your question, yes.
Glad to know this. Thanks.
 
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About 30 years ago, I asked a chemical engineer with Pennzoil Products Co. why the racing oils only had API ratings of SD when the current spec was SG. I asked if they met SG. He said that they did, but wasn't submitted for approval because they didn't want people using it in passenger cars. The amount of zinc was around 1600 ppm, and that level had shown it could cause pitting and spalling when used in normal passenger car OCIs. So to discourage its use as such, it wasn't approved or labeled with the current spec.
 
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There's no application on Earth that needs more than 1400 ppm for regular use. NHRA Stock Eliminator and Super Stock Eliminator are among the most demanding on high ZDDP oils due to having flat tappet cams with extreme lobe intensity that makes you want to question the laws of physics. They do fine on oils in the 1100-1200 ppm range. There's 2 downsides to increasing ZDDP. 1. Increased corrosion risk. Concentrations too high can neutralize other corrosion inhibitors in the oil which can increase the risk of corrosion. ZDDP is also acidic and will interact with, or possibly hinder, overbased detergents in the oil. The threshold I've known for increased corrosion is ~3%wt (~1920 ppm Zn). 2. Increased friction. As ZDDP concentration increases, so does friction in boundary and mixed lubrication regimes (and full hydrodynamic regime in high stress oil films). Different types of ZDDP have different effects on friction, but that friction also drives reactivity. It's one of the reasons ZDDP and moly based additives like MoDTC and organomolybdenum complexes pair so well together as the higher friction from ZDDP tribofilms promotes the reactivity of moly additives to counter that friction. Hugh Spikes has white papers out on his studies of ZDDP, it's tribofilm formation in different base oils and environments, it's reactivity with surfaces and other additives, and the effect of concentration on the oil service life. If you do a google search for Hugh Spikes ZDDP, it'll turn up a lot of great reading material if you are as much of a chemistry nerd as I am.
 

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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
 
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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?
 
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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
Wasn't this also a issue in older engines with more lead and copper than what we see in today's engines?
 

SR5

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Here is a link to the Mobil 1 PDF that lists their zinc levels, It's dated June 2019, and I would trust Mobil to make and sell safe oils. For zinc, regular Dexos1 rated oils are 750 to 900 ppm. M1 0W40 A3/B4 is 1100 ppm Zn (Euro Oil) M1 TDT 5W40 is 1300 ppm (CK4 HDEO) and so is M1 15W50 which they say is suitable for flat tappet application. M1 V-Twin 20W50 motorcycle oil is 1750 ppm M1 Racing is 1850 ppm Given M1 V-Twin is a popular HD motorcycle oil that many use long term without issue, then this level should be safe. M1 15W50 (API SN & ACEA A3/B3 & 1300 ppm Zn) has always been my pick as a safe performance oil for the street.
 
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^^^ to all the posts above ^^^ and great posts! This is why, as a layperson, who doesnt know, I listen to the manufacturer of the engine and use the oil recommended and completely ignore the comments in some threads that say "wow that is some stout oil" :o) I do know, too much of ANYTHING is no good as the best anti ware component of oil is the oil itself.
 
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Originally Posted by alarmguy
^^^ to all the posts above ^^^ and great posts! This is why, as a layperson, who doesnt know, I listen to the manufacturer of the engine and use the oil recommended and completely ignore the comments in some threads that say "wow that is some stout oil" :o) I do know, too much of ANYTHING is no good as the best anti ware component of oil is the oil itself.
There's nothing wrong with this line of thought. The vast majority of car owners just take their car to a quick lube place whenever the sticker or OLM tells them to and don't even know what an API rating is. I imagine the OEM recommendations (and also engine design) are made with these people in mind. We are the select few who (arguably) over-analyze our maintenance routine. This being said, the OEM recommendation doesn't mean you can't do better. They're just covering their tail ends should somebody have an engine failure occur during the warranty period. I believe the least amount of ZDDP necessary is the ideal amount as more than that just increases the 2 issues I mentioned above without additional anti-wear benefits. There's also different types of ZDDP though which can come into play at the same concentration. ZDDP isn't a single additive, but actually a family of additives. Your last statement would be true if the entire engine operated in full hydrodynamic lubrication. However, pretty much only the rod and main bearings see full hydrodynamic lubrication and even that is debatable. Every other part of the engine sees mixed or boundary lubrication where the additive package is far more influential to wear protection than the base oil.
 

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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.
 
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Originally Posted by MolaKule
When moisture and high temps enter the picture, this molecule can degrade into acids which can eventually overcome the acid-fighting base chemicals.
Does the potential corrosion also occur as the oil sits in the sump and on engine parts while the vehicle is not being used?
 
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Originally Posted by MolaKule
Borates, polymer esters, and other specialty chemicals are also included to help reduce wear.
I used to look for, and use, oils with high Boron content for my flat tappet cammed 4.9l with the reduction of Zn. I thought high Mo content would also help but later discovered it was a friction modifier. I don't bother any more because of the mild cam lift/profile and spring pressure of these engines.
 

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Do oils high in molybdenum counter some of the side effects of high zddp/phosphorus ppm?
NO, no countering effect because the Moly is a Molybdenum Dithiocarbamate which contains sulfur atoms as well. Like ZDDP it too is a Multi-Functional additive and can serve as a secondary or tertiary anti-oxidant, as well as a Friction Modifier. Below is the molecular structure of moly or Molybdenum Dithiocarbamate:

Chemical Sstructure-of-molybdenum-dithiocarbamate-MoDTC.png
 
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Originally Posted by MolaKule
Quote
Do oils high in molybdenum counter some of the side effects of high zddp/phosphorus ppm?
NO, no countering effect because the Moly is a Molybdenum Dithiocarbamate which contains sulfur atoms as well. Like ZDDP it too is a Multi-Functional additive and can serve as a secondary or tertiary anti-oxidant, as well as a Friction Modifier. Below is the molecular structure of moly or Molybdenum Dithiocarbamate:
What about organic moly compounds that don't contain sulfur such as Vanderbilt's Molyvan 855?
 

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Originally Posted by viscous
Originally Posted by MolaKule
When moisture and high temps enter the picture, this molecule can degrade into acids which can eventually overcome the acid-fighting base chemicals.
Does the potential corrosion also occur as the oil sits in the sump and on engine parts while the vehicle is not being used?
Another good question: Unless the oil is heated again to allow more acids to form, no. The most likely scenario is that rust will form on any surfaces where the oil film has disappeared, but if an oil film does remain the anti-rust component in the additive package should protect it. First off, let's recognize that these acids we are talking about and the acids that DO form are weak acids. But these weak acids over time do affect metals and have an affinity for attacking metals in the form of corrosion effects. Corrosion - General Definition: the wearing away due to chemical reactions, mainly oxidation (see oxidation-reduction, oxide). It occurs whenever a gas or liquid chemically attacks an exposed surface, often a metal, and is accelerated by warm temperatures and by acids and salts. Normally, corrosion products (e.g., rust, patina) stay on the surface and protect it. Removing these deposits reexposes the surface, and corrosion continues. Some materials resist corrosion naturally; others can be treated to protect them (e.g., by coating, painting, galvanizing, additizing, or anodizing). From one paper: [i]...It is postulated that higher acid concentrations led to the lowest continuing corrosion rate because fine particles precipitated during the rapid initial attack, and the resulting film on the metal was relatively less permeable to the corrosive fluids... So corrosion is Rate dependent whereas the initial acid formed does the most damage and the damage (continuing damage) drops off afterwards.[/i]
 

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Originally Posted by ka9mnx
Originally Posted by MolaKule
Borates, polymer esters, and other specialty chemicals are also included to help reduce wear.
I used to look for, and use, oils with high Boron content for my flat tappet cammed 4.9l with the reduction of Zn. I thought high Mo content would also help but later discovered it was a friction modifier. I don't bother any more because of the mild cam lift/profile and spring pressure of these engines.
Think of the Borates as cold temp anti-wear components in the additive while ZDDP is the high temp anti-wear additive component.
 
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Great thread. I use HPL HD, which per RDY4WAR's VOA is quite beefy. Although it is very High SAPS, this oil is advertised as having excellent anti corrosive properties. There must be some cancelling out going on here, with the add pack/base stocks involved. I use Costco gas with its 10% ethanol, and consider corrosion prevention to be an issue.
 
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