Oil Supplement - EOS

A piece of interesting information from a chemist friend......



ZDDP (also referred to as ªzincº or ZDTP) is the acronym used for

zinc dialkyldithiophospate. ZDDP is used in motor oils to inhibit

oxidation of oils and to reduce engine wear. We are concerned here

primarily with its antiwear properties. Surprisingly, the exact way

in which ZDDP prevents wear is not known. One thought is that

when part of a modern motor oil, ZDDP plates out on the engine's

iron surfaces, including bearing surfaces and cam surfaces. If a

surface gets very hot, as happens when there is a large amount of

friction, the weak sulfur (or thio) bond is broken. This causes zinc

or zinc phosphate to be plated out on the bearing surface so that the

zinc or zinc phosphate becomes a sacrificial metal or salt. This

means the plated-out zinc or zinc phosphate is worn away rather

than the bearing surface. It's easy to see why it is desirable to have

ZDDP in a motor oil.

However, ZDDP does have some undesirable properties.

Surprisingly, it increases friction, not a good thing for a motor oil.

In addition, because it plates out on surfaces and the residual

phosphorus leaves an ash, too much ZDDP can foul spark plugs. Thus, as with most additives found in modern motor oils, the use of ZDDP must

be balanced by the amount of other additives. In the case of ZDDP,

it is especially important to have neither too much nor too little

detergent in the oil. Finally, too much ZDDP can attack the

boundary grains of iron. (I have also read in several places but

cannot confirm that excess ZDDP can produce sulfuric acid as it

breaks down.)

So what is the history of ZDDP in motor oils?

ZDDP was first used in motor oils developed for aircraft engines

around 1942. Oils with a phosphorus level in the 0.03% range (or

300 ppm phosphorus by weight) were able to pass a corrosion test

introduced in 1942. Many of these engines were air cooled, run at

high rpm's and at high loads, i.e., conditions fairly different from

how our flathead engines were designed and operated. Around

1947, ZDDP was commercialized for automotive use.

In the mid-1950's, the phosphorus level from ZDDP was increased

to about 0.08% to deal with the friction caused by the use of highlift

camshafts, which increased the potential for scuffing and wear.

At this time, new tests of valve-train scuffing and

wear were developed by the automotive industry.

Also about this time, the industry discovered that more ZDDP was

not better. Although using more phosphorus reduced scuffing at

break in, longer term wear increased at phosphorus levels above

0.14%. In addition, at levels of about 0.20% phosphorus, the

ZDDP attacks the grain boundaries of iron, which can result in

camshaft spalling.

Oil thickening emerged as a problem in the 1960's with the higher

heat of high-load engines, e.g., those in muscle cars. Oils were

oxidizing and thickening to the point that engines could no longerpump it. In response, more ZDDP was added to motor oils as an

inexpensive antioxidant, raising levels of phosphorus to about 0.10%.

However, it has been found that ZDDP causes problems with the

longevity of the catalytic converters used for emission control in

modern cars. It poisons the catalytic converters and the residual ash,

caused by ZDDP combustion, clogs them. With cars lasting much

longer, the US Environmental Protection Agency began restricting the

amount of ZDDP in motor oils. The eventual goal is to have catalytic

converters last for 150,000 miles by 2009. Ironically, the long lives of

modern engines, caused in large part by modern motor oils themselves,

meant that the oils had to be reformulated. This reformulation has

occurred over several years. Since modern cars have roller lifters or

tappets, lower levels of ZDDP are not a problem for them. Most of our

flathead engines have been operated since 2001 using motor oils with

lower levels of ZDDP.

Using data supplied by the oil industry, we can list the approximate

recent levels according to year.

API Designation Year Percent Phosphorus

SH 1996 0.120

SJ & SL 2001&2004 0.100

SM 2005 0.080

The level of ZDDP in motor oil with the API designation of SM is

about the same as was used in the latter part of the 1950's. Our

flathead engines are not experiencing reduced levels of ZDDP. Instead

they are experiencing higher levels than were present in motor oils

when the engines were new.

In addition, it is not true that older engines have not been considered in

the reformulation. Because backward compatibility is important, the oil

industry has developed other types of antiwear and antioxidant

additives to compensate for the lower amount of ZDDP in motor oils.

These additives are now being used in current motor oils. It appears

that these additives are based upon boron and/or molybdenum.

In addition, two tests (also known as sequences) of motor oil, while not

using flathead engines, do use engines with valve trains that do not

contain roller followers (i.e., the engines had followers with sliding

friction, just like our flatheads). Sequence IVA uses a single overhead

cam engine with slider finger followers to test for camshaft scuffing

and wear. Sequence IIIG uses a V6 engine with a flat-tappet system to

check cam and lifter wear.

So What's the Problem?

There have been many reports of catastrophic failure of valve trains in

the last three years or so. Most of these appear to have occurred in

newly rebuilt engines with overhead valve engines equipped with flat tappet lifters, i.e., not equipped with roller tappets. However, as you

might expect, most of these engines had much stiffer valve springs than

found in our flathead engines. Over about the same period that ZDDP was being reduced in

motor oils, many U.S. suppliers of flat-tappet lifters reduced

capacity or closed production. As a result, many engine

rebuilders of high performance engines turned to lifters made by

off-shore companies. Reportedly these valve train components

too often used inferior metallurgy, poor finishes and improper

radii. (They were, however, affordable and available.)

Some other engines did not have catastrophic failure but instead

suffered non-catastrophic failure. Their valve train components

simply wore at an alarming rate. Reports for this type of failure

occurred in older pushrod, air cooled Porsches and motorcycles,

which is not really a surprise when you consider that ZDDP was

originally developed for air-cooled engines. Air-cooled engines

can have more stresses due to the fact that, compared to watercooled

engines, their operating temperature is more variable and

engine tolerances are often larger to account for more thermal

expansion.

The article I mentioned at the beginning of this article had a

chilling story of a 1946 Cadillac with a flathead engine. The

bronze gear failed very quickly when operated with a SM oil.

However, attributing this to the lower ZDDP levels in the SM

oil is incorrect for several reasons. First, the sample size was

simply too small to draw conclusions, i.e., there were too few

tests of too few bronze gears. Second, most commercial oils in

1946 didn't have ZDDP. If reduced ZDDP is a problem,

certainly all 1946 Cadillac engines would have failed quickly.

Finally and most convincingly, ZDDP does not act as an

antiwear additive for bronze metals. Remember it acts only on

metals containing iron. Something else had to be responsible

for the bronze gear failure. In my opinion, the bronze itself is

suspect. The machine shop that made the gears did not follow

the specs for the original bronze gear. Instead, they ªfound

material that they felt would be satisfactory.º I suspect those

materials were not satisfactory.

What does this mean for our flathead engines?

Unfortunately, there is more opinion than hard data on this

subject (and that includes this article). This makes it especially

important to check what facts we do have:

Fact: The motor oils used by our flathead engines when they

were new did not have ZDDP. Our engines lasted a long time

while using oil with no or low ZDDP.

Fact: While ZDDP is reduced in current motor oils, it is still

about the same level that was present in the mid-1950's, when

the heavier valve trains of overhead valve engines required it.

And those levels of ZDDP solved that problem.

Fact: Most of the catastrophic failures of valve trains occurred

in newly rebuilt engines with flat tappets during a period when

many cams of suspect quality were supplied by off-shore

manufacturers.

Fact: Despite several years of use of the newly formulated oils,

there have been no wide-spread reports of failures of valve

trains in our flatheads, in contrast to what you would

expect if there were a severe problem with these oils.

Fact: The oil industry strives to make oils backward compatible

and there are two sequences with engines somewhat similar to

our engines in terms of flat tappets. All of the current oils with

the SM designation must pass this test.

Continued on next post......

"A little does good" springs to mind. From the time unleaded fuel has been used exclusively here thee has been a product available at Service stations, and elsewere, know as Valvemaster. this is a phosphorous based substance which is designed to take the place of lead in protecting the valves and seats, leaving a microscopic surface residue which acts as a lubricant. It is designed to be used at a maximum doasage of one shot per 40 litres of petrol, and seems to perform it's job pretty well. What is not know of course is if any harm can come bynot using it, but that is probably another story. However, what has been established, is that some people with older cars have taken the attitude "If a little does, a lot must do heaps better". WRONG. Over-use of this additive has the same effect as the old super-leaded fuels, which left ash and residues on the valve faces, seats, stems and guides, leading to valve sticking and burning. In this layman's view, the oils supplied by the trade are quite capable of lubricating our old engines in far superior manner than the oils which were in use when our cars were originally manufactured. Now I'm going to sprinkle peanuts all over the front lawn to keep the tigers away.