Subject: Re: [TR] Engine oil

From: "Randall" <[email-masked]>
Date: Tue, 16 Jul 2013 07:27:01 -0700

> I have a query 
> here..........what is ZDDP?

Zinc Dialkyl Dithio Phosphate (or something like that anyway).  You've heard
all the hype about oil additives that "bond with the metal" and form a
"barrier against wear" ... Well, ZDDP really does that.  I don't claim to
fully understand it, but in the presence of bare steel, the ZDDP breaks down
and leaves a microscopically thin layer of phosphate on the steel.  Once the
steel is coated, the process stops and the rest of the ZDDP doesn't do
anything until it finds some bare steel again (or gets flushed out when you
change oil).

However, if the normal oil film breaks down and allows metal-to-metal
contact, the phosphate layer acts as a solid lubricant to reduce wear.  In
addition, it is what wears away first and then gets replenished from the oil
(if there is still ZDDP available in the oil).  

The most common place for this to happen is the tip of the cam lobes, on
engines (like our Triumphs) that don't use a roller bearing between the lobe
& lifter.  Frequently known as "flat tappet", even though they aren't really
flat.  

Unfortunately, the zinc & phosphorus atoms are poisonous to the catalytic
converters used to reduce exhaust emissions on modern cars.  So the US EPA
got together with the oil makers and persuaded them to drastically cut back
on the ZDDP content in the oils, so the catalytic converters would last
longer.  IIRC the stated goal was to push the expected life of the emissions
control systems out to 200,000 miles instead of the current 100,000.

The new oils do still have some ZDDP, just much less (roughly half as much
as before).  At least in theory, as long as the ZDDP isn't all gone by the
time you change oil, then more won't help (and may have some bad effects,
too much is worse than too little).

-- Randall 

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