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Motorcycle oil additives Part 2: ZDDP

Posted by: Erik Bjornstad

The market for oil additives targeted at motorcycle owners is littered with magic formulations all claiming to be the latest and greatest thing.  Motorcycle owners are willing to spend a lot of money on their bikes.  But nobody wants to feel like they're being taken advantage of. Unfortunately, in the field of oil treatments, a lot of that goes on.

Choosing_the_Right_Type_of_Fuel_for_Your_MotorcycleRecently, we discussed one of the popular magic ingredients in oil additives, PTFE (Teflon). We talked about how, despite grand claims by the additives makers, PTFE doesn't really bonds to metal surfaces and turn your engine into a non-stick frying pan.  Dupon (the makers of Teflon) even tried to refuse to sell it to these additive makers, but lost a lawsuit which forced them to continue to sell, based on the legal principle that you can't refuse to sell something to someone just because you think they'll misuse it.  Now, let's look at another one of the popular secret ingredients in motorcycle oil additives and see if it's everything it's cracked up to be.

Zinc-Containing Oil Additives For Motorcycles

There is another popular oil additive ingredient called ZDDP, the primary ingredient in the second (of four) main class of oil additives for motorcycles.  ZDDP is well known within the lubricant industry for being an excellent extreme-pressure additive. For years, virtually all motor oils contained some level of ZDDP content, because it was one of the best known compounds of its kind for providing extreme protection.  Some time seven or eight years, the EPA started putting pressure on the oil formulators to reduce the amount of ZDDP in standard motor oils. The reason for this was the P in ZDD'P' - P stands for phosphorus. Experiences out in the field found that older engines which experienced any kind of blowby where the oil leaked into the combustion chamber - these engines now had phosphorus finding its way to the catalytic convertor. Phosphorus and catalytic convertors do not mix at all. So the EPA found catalytic convertors being damaged or deactivated by the phosphorus in the oil.  The industry did push back some and was able to preserve a lower level of ZDDP in the oil.  But if the EPA had its way, it would be gone entirely. 

And so now, here we are. These days, all motor oils contain some level of zinc, typically betwen 0.10 and 0.20 percent. Oil additive formulators know that older motorcycle owners well remember the days when men were men and motor oil had lots of zinc in it. Hence why you see so many oil additives with marketing languaged aimed at this group. The classic car market is also like this - just google something like 'classic car oil additives' and you'll see pages of oil additives boasting about boosting the zinc level in the oil and how excellent that is.

If zinc and ZDDP are such great additives, is there anything bad to say about them? There were plenty of negative things to say about Teflon, so what about zinc?

First, we have to couch any further comments in the repeated truth that the ZDDP compound IS a really good wear protector. It's not like Teflon which doesn't do what's expected. So it becomes an issue of necessity.  As a bike owner, do you really need to spend $20 or $40 however much it is for an awesome new oil additive with lots of zinc therein?  

To properly answer the question, we have to consider a few things.

First, ZDDP works when it is activated by metal-to-metal contact.  When this happens, it turns the ZDDP into a friction-fighting compound on the metal's surface - "activates it", so to speak.  But most motorcycles under normal operating conditions don't have much metal-to-metal contact. So this means that for the 99.99% of the time the engine isnt undergoing this catastrophic situation, the zinc is merely a bystander in the oil.

Second, when it comes to zinc, more isn't always better. Too much zinc in the oil is associated with spark plug fouling and valve deposit formation. Some additional ZDDP provides benefit, but you don't need to spend a bunch on some super-charged additives with tons of zinc, as it may do more harm than good.

Also keep in mind that some of these additives with newer versions of zinc in them are labelled with warnings about being eye irritants. So if you see that warning label, use safety goggles when using the product.

You may be interested in these other posts about motorcycles:

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This post was published on November 25, 2014 and was updated on November 25, 2014.

Topics: Motorcycles