Engine Oil Mythology

-

d1970

TODAY IS A GOOD DAY TO HAVE A GOOD DAY
Joined
Sep 29, 2015
Messages
465
Reaction score
300
Location
Ontario, Canada
Interesting reading about motor oil

Engine Oil Mythology

Thanks to Bob Olree – GM Powertrain Fuels and Lubricants Group

GMPT – Fuels & Lubes

Myths are ill-founded beliefs held uncritically by interested groups. Over the years there has been an overabundance of engine oil myths. One was that the only good oils were oils made from “Pure Pennsylvania Crude Oil.” This one got started before the Second World War when engine oil was crude oil with very minimal refining, and crude oil from Pennsylvania made better engine oil than Texas or California crude. With modern refining, almost any crude can be made into good engine oil.

The next myth was that “modern” detergent engine oils were bad for older engines. This one got started after the Second World War, when the government no longer needed all the detergent oil for the war effort, and it hit the market as Heavy-Duty oil. These new detergent oils gave the pre-war cars, which had been driven way past their normal life and were full of sludge and deposits, a massive enema. In some cases bad things happened such as increased oil consumption – the piston rings were completely worn out and the massive piston deposits were the only thing standing between merely high and horrendous oil consumption. If detergent oils had been available to the public during the war, this myth never would have started.

Amazingly there are still a few people today, 60 years later, who believe that they need to use non-detergent oil in their older cars. Apparently it takes about 75 years for an oil myth to die.

Then there is the myth that new engines will not break-in on synthetic oils. Apparently there was an aircraft engine manufacturer who once put out a bulletin to this effect. Clearly the thousands and thousands of cars filled with Mobil 1 as factory-fill, which have broke-in quite well, should have put this one to rest. However this one is only 40 years old, so it has another 35 years to live.

All of these myths have a common theme; newer oils are bad. And this brings us to the latest myth – new “Starburst”/ API SM engine oils are bad for older cars because the amount of anti-wear additive in them has been reduced. This one has gotten big play in the antique and collector car press lately. The anti-wear additive being discussed is zinc dithiophosphate (ZDP).

Before debunking this myth we need to look at the history of ZDP usage in engine oil.

ZDP has been used for over 60 years as an additive in engine oils to provide wear protection and oxidation stability. Unfortunately, ZDP contains phosphorus, and phosphorus is a poison for automotive catalysts. For this reason ZDP levels have been reduced by about 35% over the last 10-15 years down to a maximum of 0.08% for “Starburst”/API SM oils.

Zinc dithiophosphate was first added to engine oil to control copper/lead bearing corrosion. Starting in 1942, a Chevrolet Stovebolt engine with aftermarket copper/lead insert bearing connecting rods was the standard oil test. The insert bearings were weighed before and after test for weight loss due to corrosion. The phosphorus levels of oils that passed the test were in the 0.03% range.

In the mid 1950s Oldsmobile got in a horsepower war with its Rocket engine against the Chrysler Hemi. Both companies went to high-lift camshafts and both got into camshaft scuffing and wear problems very fast. There were three solutions. Better camshaft and lifter metallurgy, phosphating the camshaft, and increasing the phosphorus level from ZDP up to the 0.08% range. Another outcome was a battery of industry wide “Sequence” oil tests. Two of theses tests were valve-train scuffing/wear tests.

Knowing that this higher level of ZDP was good for flat-tappet valve-train scuffing and wear, some oil companies dumped even more in thinking that they were offering the customer even more protection. However it was soon learned that while going above something like 0.14% phosphorus might decrease break-in scuffing, it increased longer term wear. At about 0.20% phosphorus the ZDP started attacking the grain boundaries in the iron, resulting in camshaft spalling.

Later in the 1970s, the ZDP level was pushed up to the 0.10% phosphorus range as it was a cheap and effective antioxidant, and increased antioxidancy was needed to protect the oil in Cadillacs pulling Airstream trailers from thickening to the point of not pumping. Recently, the need for this higher level of ZDP for protecting the oil from thickening has been greatly reduced with the introduction of more modern ashless antioxidants that contain no phosphorus.

Enough history, now getting back to the myth that “Starburst/API SM oils are no good for older cars. The argument put forth by the myth believers is that while these oils work perfectly well in modern gasoline engines equipped with roller

camshafts, they will cause catastrophic wear in older engines equipped with flat-tappet camshafts.

The “Starburst”/API SM oil standards were developed by a group of OEM, oil additive company, and oil company experts. When developing any new engine oil standard the issue of “backward compatibility” always comes up, and indeed the group of experts spent a lot of time researching this issue. Various oil and additive companies ran “no harm” tests on older cars with the new oils. No problems were uncovered.

The new specification contains two valve-train wear tests. One is the Sequence IVA Test which tests for camshaft scuffing and wear using a 2.4L Nissan single overhead camshaft engine with slider finger followers. The wear limits were tightened from the previous oil specification which contained a phosphorus limit of 0.10%. The second is the Sequence IIIG Test which evaluates cam and lifter wear. A current production GM Powertrain 3.8L engine with the valve train replaced with a flat tappet system similar to those used in the 1980s is used. The only reason that this test engine uses this older valve train design is to insure that older engines are protected. All “Starburst”/API SM oil formulations must pass these two tests.

In addition to the protection offered by these two valvetrain wear tests and the new testing which was conducted on the formulations containing lower levels of ZDP, a review of the knowledge gained over the years in developing previous categories also indicates that no problem should be expected. The new “Starburst”/API SM oils contain about the same percentage of ZDP as the oils that solved the camshaft scuffing and wear issues back in the 1950s. They do contain less ZDP than the oils that solved the oil thickening issues in the 1960s, but that is because they now contain high levels of ashless antioxidants that were not commercially available in the 1960s.

The oil’s ZDP level is only one factor in determining the life of an older camshaft or a new aftermarket camshaft. Most of the anecdotal reports of camshaft failures attributed to the newer oils appear to be with aftermarket camshafts. Breaking in extremely aggressive aftermarket camshafts has always been problem. The legendary Smokey Yunick wrote that his solution to the problem was to buy multiple camshafts and simply try breaking them in until he found one that survived break-in without scuffing.

Despite the pains taken in developing special flat tappet camshaft wear tests that these new oils must pass and the fact that the ZDP level of these new oils is comparable to the level found necessary to protect flat tappet camshafts in the past, there will still be those who want to believe the myth that “new oils will wear out older engines.” Like other myths before it, history teaches us that it will take about 75 years for this one to die also.

February 13, 2007
 
Very interesting read. I will continue to add a little zddp to each oil change to be safe. I think my next build will be a roller cam anyway.
 
While i agree with the reading I believe there is a difference in oil for older engines. Optimally you want a oil with high zinc and phosphorus ppm. You can take a look at mobile ones site. There is noticeably more zinc and phosphorus in their 15w50 than in their 5w20. Most of the lighter weight oils are lower on the content because newer engines dont need as much as older engines and the emission issue plays a role as well
 
Last edited:
i have raised the zinc argument before and you cannot find anybody who isn't convinced it is necessary for flat tappet cams.
It has become a tremendous money maker.
 
i have raised the zinc argument before and you cannot find anybody who isn't convinced it is necessary for flat tappet cams.
It has become a tremendous money maker.

Sure. Just as Sulfur isnt ''necessary" in diesel fuel for a diesel engine to run but it sure helps.
im sure the older engines would run just fine on a oil with a lower zinc and phosphorous ppm but i believe it helps in longevity concerning wear.

Just as is when the gas had lead in it. now its all lead free, sure it runs off of it with no issues but there were benefits to the lead.

but along with everything the epa changes it constantly and thats what really determines whats available to use
 
Great article, although it's a bit dated.
I don't buy the bullcrap statement that GM (or Ford for that matter) doesn't know how to build cars or engines that a lot of people have the opinion of on here.
I am also surprised that with today's modern technology, that a flat tappet cam should need to be broken in. (Even though i know it does).
What would be cool is if you could buy a matched cam and lifter set that was already broken in from the manufacturer.
Another point to make here is that with modern machining practices, the finish on the cylinders is much more refined as well as piston ring technology has come a long way to allow modern synthetic oils to be used in engines from first start up without ''break in issues'' for the cylinders.
Try that with a rough finish and cast iron rings, and the engine would never break in properly.
That's one of the reasons that a lot of people are against using synthetic oils in older engines.
Kinda makes you wonder about how good synthetic oils really are if they are ''too slippery'' to allow an engine to break in using old machining practices.........
I use a zinc additive when using dino oil in my older cars too, it's not worth it to me to take a chance.
 
Great article, although it's a bit dated.
I don't buy the bullcrap statement that GM (or Ford for that matter) doesn't know how to build cars or engines that a lot of people have the opinion of on here.
I am also surprised that with today's modern technology, that a flat tappet cam should need to be broken in. (Even though i know it does).
What would be cool is if you could buy a matched cam and lifter set that was already broken in from the manufacturer.
Another point to make here is that with modern machining practices, the finish on the cylinders is much more refined as well as piston ring technology has come a long way to allow modern synthetic oils to be used in engines from first start up without ''break in issues'' for the cylinders.
Try that with a rough finish and cast iron rings, and the engine would never break in properly.
That's one of the reasons that a lot of people are against using synthetic oils in older engines.
Kinda makes you wonder about how good synthetic oils really are if they are ''too slippery'' to allow an engine to break in using old machining practices.........
I use a zinc additive when using dino oil in my older cars too, it's not worth it to me to take a chance.

Not sure if full synthetic oils would do well in a older un touched engine but my engine builder who built my 340 reccomended mobil 1 full synthetic and says he does for all his engines. its nice to have a engine builder with full synthetic in mind when they are bulding it. but really on a rebuilt engine you should be able to use either. as long as you use proper break in oil it should be fine.
 
Not sure if full synthetic oils would do well in a older un touched engine but my engine builder who built my 340 reccomended mobil 1 full synthetic and says he does for all his engines. its nice to have a engine builder with full synthetic in mind when they are bulding it. but really on a rebuilt engine you should be able to use either. as long as you use proper break in oil it should be fine.
Absolutely.
Great to hear your engine builder is on board for the full synthetics in your new build and is doing the machining to accomplish it.
An older broken in already engine in good shape would do great with synthetics, but, a worn out engine or one that was prepped the old way wouldn't break in properly until the first couple of oil changes with dino oil.
It's all about cylinder prep and the style of rings used.
Yes, i have seen first hand the results all of the way around, and i'm convinced that synthetics are the way to go if everything's right.........
 
i'm sure full synthetics are superior...but i have seen many engines go well over 500k
on regular dino oil.
 
-
Back
Top