stp oil additive with zddp, and high mileage,good?

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I never cared much for STP Oil Treatment myself. It is basically thick oil with some chemical additives, and according to VOAs here it has a low amount of ZDDP. Newer vehicles require thinner oil and STP basically will just slow down oil consumption in an oil burner. Even in an oil burner a person might be better off just using thicker oil, like 20W50.

The one time I noticed a difference with STP was with a small car and the STP they used to have for small four cylinder engine cars. The car really did seem to run better.

I did not know they even still made STP.
 
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Originally Posted By: Mystic
I never cared much for STP Oil Treatment myself. It is basically thick oil with some chemical additives, and according to VOAs here it has a low amount of ZDDP. Newer vehicles require thinner oil and STP basically will just slow down oil consumption in an oil burner. Even in an oil burner a person might be better off just using thicker oil, like 20W50.

Absolutely. If you want a thicker oil, buy a thicker oil. If you want more ZDDP, buy an oil that has more (which is probably going to be thicker, too).
 
Question. If too much zinc can cause corrosion, why is zinc used as sacrificial anodes to protect marine metals such as aluminum and steel? Zinc would be the least noble metal of any metal found in an engine. What about the phosphorous that accompanies zinc, or the dithiophosphate compound? I have seen cam surfaces with rust pocks on them where the mechanic called it zinc poisoning. Furthermore, zinc corrosion seems to be magnified in a marine environment, or at least that is what I have been told. I am by no means a chemist, but know enough to sound dumb. My boat with over 2500 hours on it had zero internal corrosion on a teardown and it has seen 1600PPM zinc oil since day one. I have gone as far as 220 hours on an OCI as well.
 
Maybe Mola will read this and share his insights. As for the "limits" I place on ZDDP content, I'm probably being conservative. But, there is a point of diminishing returns even before spalling occurs, if I recall correctly.

As for zinc anodes to protect from corrosion versus spalling inside an engine, an aqueous solution is totally different from the environment inside an engine.
 
Originally Posted By: Michael_P
Question. If too much zinc can cause corrosion, why is zinc used as sacrificial anodes to protect marine metals such as aluminum and steel? Zinc would be the least noble metal of any metal found in an engine. What about the phosphorous that accompanies zinc, or the dithiophosphate compound? I have seen cam surfaces with rust pocks on them where the mechanic called it zinc poisoning. Furthermore, zinc corrosion seems to be magnified in a marine environment, or at least that is what I have been told. I am by no means a chemist, but know enough to sound dumb. My boat with over 2500 hours on it had zero internal corrosion on a teardown and it has seen 1600PPM zinc oil since day one. I have gone as far as 220 hours on an OCI as well.


Cathodic protection is due to an electro-chemical effect and can hardly be compared to surface interactions in tribology.

Here is a good explanation of cathodic protection and sacrificial anodes:
Cathodic Protection

But you're right Michael, it the concentration of phosphorous and sulfur in the ZDDP molecule.

Zinc Dialkyl Dithiophosphates or ZDDP (or Dithiophosphoric Acid, O,O'-Isobutyl Amyl Ester, Zinc Salt ) is an ester which is used as an Anti-Wear agent and an Anti-Oxidant agent (a multifunctional additive) in oil additives and is composed of the elements of zinc, phosphorous, and sulfur.

When concentrations get above approx. 1200 ppm, and when under high moisture conditions and extremely high temperatures, there is the potential for the ZDDP molecule to split apart (via hydrolosis) and form acids attacking the metals as acids of sulfuric and phosphoric acid.

Marine oils, both gear lubes and PCMO's, as well as classic car and HDEO oils, have a higher level of anti-corrosion agents which tend to combat any acid attack. Most Marine engines also tend to run cooler, only to expel moisture at WOT when hot.
 
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Great explination MolaKule. Thanks.
So would a higher TBN combat this or are anti corrosion agents needed for this?
 
The tbn is primarily deterrmined by the calcium or sodium detergents.

Quote:
Detergents (Surface Protective Additive): metallo-organic compounds of sodium, calcium, magnesium, boron phenolates, phosphates and sulfonates such as alkylbenzene sulfonic acids, alkylphenol sulfides, alkylsalacyclic acids; Lift deposits from surfaces to keep them suspended.


The corrosion inhibitors include some additional agents that include Metal Deactivators and Rust inhibitors:

Quote:
Metal Deactivator (Protective Additive): ZDDP, ZTDC, Moly TDC, Antimony TDC, family of diphenylamines and amides, and olefin sulfides, heterocyclic sulfur-nitrogen compounds; inhibits corrosive effects of oxygen with metals and decreases metal interaction with oxygen compounds to reduce oxidation of oil.

Rust Inhibitor (Surface Protective Additive): Barium sulfonates, amine phosphates, phosphordithioates, sodium thizoles (for coolants),


Chemistry of Additives
 
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