Are zinc and phosphorus sacrificial?

[ccdhowell]

I've been thinking about this for a little while. I've used Torco T4MXR in a couple of my race quads for 2+ years now. Over that time I've done several used oil analysis with zinc and phosphorus varying by several hundred ppms(zinc low of 936 and high of 13,26 ppm). Now I have used Torco in these engines exclusively since they were new so I'm not getting any readings skewed by switching from another oil.

So my question is, why the variance in zinc and phosphorus over time? Is it because they are sacrificed when two surfaces go metal-to-metal? Would lower zinc and phosphorus numbers in my situation indicate that I have been more abusive to my engines over that oil run? Or is it just an expected variance in sampling? Or perhaps a change in oil formulation over time?

 

[toneydoc]

That is REALLY deep thinking. Yes,racing is abusive to your engines. Why do you think that the NASCAR fellas rebuild and replace after a single race. Abuse and wear of parts.

You could very well have a variance due to sampling. And oils do change in their mixes.

How are the engines doing these days? Any problems? If not, count your lucky stars and keep the pedal to the metal. I hope you are winning from time to time.

 

[CATERHAM]

The AW element of the ZDDP molecule is phosphorus (P) which plates on metal surfaces at moderately high engine temp's.
But while the P is worn away in boundary lubrication, I don't think it's sacrificial as it is constantly being replaced as long as the engine substrate temp's are sufficiently high enough.

 

[edhackett]

It's more complicated than that. It takes breakdown components of the ZDDP that contain both P and Zn and the S to form the anti-wear film. It is sacrificial in the extent that the ZDDP is decomposed to form the film and is constantly refreshed. Eventually there are no "reactive" molecules left. UOA won't show this as the Zn and P are still there, just in non-useful form.

Here's a good paper on the subject(download the PDF):

http://www.springerlink.com/content/v6u82p85wr4237p2/

Ed

 

[ccdhowell]

toney, very little trouble considering the abusive nature of cross country racing, but I am obsessive with maintenance. Yeah, I place well sometimes, my last win came in the first race last season. Luckily I play the consistency card, I won my class championship in 2010.

CATERHAM, assuredly the engines reach a sufficiently high temperature during a 2 hour race, so the molecules would regenerate from their "lesser" parts?

ed, I can't download the pdf, don't want to pay for it. What do you mean by "reactive" molecules? Seems that if the molecule still exists as a phosphorus, etc. molecule that it would be reactive. Are you saying that these AW molecules will shear into two or more different elements? Difficult to believe, but inside of a wet clutch 450 quad engine at full song is a terribly harsh environment so I wouldn't discount it.

 

[edhackett]

My employer apparently has a subscription. I can't get it here at home. I'll post some relevant parts on Tuesday.

In short, yes the ZDDP molecule shears. At low temperatures the ZDDP does form a cushion, better than nothing, but not by much. The real protection comes once everything gets up to temperature. When metal to metal contact occurs the ZDDP reacts(shears) into various molecules that then react with the iron to form a hard anti-wear coating. Only specific breakdown products can form the film. Once the Zn and P have reacted to form compounds that are not able to form that film their anti-wear properties are lost.

If you have seen the references here on this site that claim used oil protects better than new, that is the result of bench tests that illustrate this action. The used oil contains the byproducts of the ZDDP shearing that are more readily able to form an anti-wear film. The first reaction has been done to some proportion of the ZZDP molecules. These tests don't really apply to everyday engine operation as they were performed on clean metal. Your engine has the anti-wear film in place from the previous oil.

Another thing regarding ZDDP is that more doesn't give you better protection. An oil that has enough to reach the threshold of protection offers all the protection that can be used. Engines that have, for example, flat tappets and high pressure valves springs rely heavily on an anti-wear additives such as ZDDP. Oils that have higher concentrations maintain the above threshold levels as the ZDDP is "used up" by the metal to metal contact.

Ed

 

[ccdhowell]

Thanks ed, that info is new to me, didn't actually see it happening like that. Just always assumed the ZDDP molecule remained intact and protected as an intact molecule. I would be interested in more from this article if you can post it.