Oil weight and additives

[man114]

I hear in some markets they specify thicker oil than 5w20. I’d like to verify if it’s true. The reason being I’d like to add a small amount of ZDDP additive to the synthetic oil but it would slightly thicken the oil. I have my reasons for this. They’ve basically removed it to extend the life of catalytic converters. I call BS since my 83 Grand marquis had high ZDDP oils for years and is still on the original cats. It does help wear, I’ve tested it in a bunch of small engines.

If it extenuated the life of the engine I’d be well past any warranty anyway. I use it in a few other vehicles such as my 06 Fusion which still sounds better than most of those of a similar age and mileage.

[Top_Fuel]

...I’d like to add a small amount of ZDDP additive
...It does help wear, I’ve tested it in a bunch of small engines.

Have you ever had an oil analysis test done?

You may want to check out this thread. I probably have the most analyzed engine oil of any Mirage on the planet.

[Fummins]

I should do an oil analysis on a few of our cars one day. I'm curious how the high k car is doing. It's run 0w20 mobil for the first year or so then switched to klondike 0w20 for the last few. Change it every 12k kms/7450miles and use the mitsubishi filter.

[Loren]

ZDDP is almost a requirement for an engine with an old-school flat-tappet camshaft. But, for a modern engine that was designed to work with modern oil, you're wasting your money putting ANY kind of additive in the oil.

This is a really good read.

I'm with Fummins on this. Use the factory specified 0w20 synthetic oil and change it every 7-10k miles. I wouldn't hesitate to go 12k miles if I drove that much in a year.

[Eggman]

This is a really good read.

That is a good read indeed.

Over the years there has been an overabundance of engine oil myths. Here are some facts you may want to pass along to customers to help debunk the fiction behind these myths.

The Pennsylvania Crude Myth -- This myth is based on a misapplication of truth. In 1859, the first commercially successful oil well was drilled in Titusville, Pennsylvania.
A myth got started before World War II claiming that the only good oils were those made from pure Pennsylvania crude oil. At the time, only minimal refining was used to make engine oil from crude oil. Under these refining conditions, Pennsylvania crude oil made better engine oil than Texas crude or California crude. Today, with modern refining methods, almost any crude can be made into good engine oil.

Other engine oil myths are based on the notion that the new and the unfamiliar are somehow "bad."

The Detergent Oil Myth -- The next myth to appear is that modern detergent engine oils
are bad for older engines. This one got started after World War II, when the government no longer needed all of the available detergent oil for the war effort, and detergent oil hit the market as “heavy-duty” oil.

Many pre-war cars had been driven way past their normal life, their engines were full of sludge and deposits, and the piston rings were completely worn out. Massive piston deposits were the only thing standing between merely high oil consumption and horrendous oil consumption. After a thorough purge by the new detergent oil, increased oil consumption was a possible consequence.

If detergent oils had been available to the public during the war, preventing the massive deposit buildup from occurring in the first place, 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 many years for an oil myth to die.

The Synthetic Oil Myth -- Then there is the myth that new engine break-in will not occur with synthetic oils. This one was apparently started by an aircraft engine manufacturer who put out a bulletin that said so. The fact is that Mobil 1 synthetic oil has been the factory-fill for many thousands of engines. Clearly, they have broken in quite well, and that should put this one to rest.

The Starburst Oil Myth -- The latest myth promoted by the antique and collector car press says that new Starburst/ API SM engine oils (called Starburst for the shape of the symbol on the container) are bad for older engines because the amount of anti-wear additive in them has been reduced. The anti-wear additive being discussed is zinc dithiophosphate (ZDP).

Before debunking this myth, we need to look at the history of ZDP usage. For over 60 years, ZDP has been used as an additive in engine oils to provide wear protection and oxidation stability.

ZDP was first added to engine oil to control copper/lead bearing corrosion. Oils with a phosphorus level in the 0.03% range passed a corrosion test introduced in 1942.

In the mid-1950s, when the use of high-lift camshafts increased the potential for scuffing and wear, the phosphorus level contributed by ZDP was increased to the 0.08% range.

In addition, the industry developed a battery of oil tests (called sequences), two of which were valve-train scuffing and wear tests.

A higher level of ZDP was good for flat-tappet valve-train scuffing and wear, but it turned out that more was not better. Although break-in scuffing was reduced by using more phosphorus, longer-term wear increased when phosphorus rose above 0.14%. And, at about 0.20% phosphorus, the ZDP started attacking the grain boundaries in the iron, resulting in camshaft spalling.

By the 1970s, increased antioxidancy was needed to protect the oil in high-load engines, which otherwise could thicken to a point where the engine could no longer pump it. Because ZDP was an inexpensive and effective antioxidant, it was used to place the phosphorus level in the 0.10% range.

However, phosphorus is a poison for exhaust catalysts. So, ZDP levels have been reduced over the last 10-15 years. It's now down to a maximum of 0.08% for Starburst oils. This was supported by the introduction of modern ashless antioxidants that contain no phosphorus.

Enough history. Let's get back to the myth that Starburst oils are no good for older engines. The argument put forth 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 facts say otherwise.

Backward compatability was of great importance when the Starburst oil standards were developed by a group of experts from the OEMs, oil companies, and oil additive companies. In addition, multiple oil and additive companies ran no-harm tests on older engines with the new oils; and no problems were uncovered.

The new Starburst specification contains two valve-train wear tests. All Starburst oil formulations must pass these two tests.

- Sequence IVA tests for camshaft scuffing and wear using a single overhead camshaft engine with slider finger (not roller) followers.

- Sequence IIIG evaluates cam and lifter wear using a V6 engine with a flat-tappet system, similar to those used in the 1980s (fig. 5).
figure 5

Those who hold onto the myth are ignoring the fact that the new Starburst oils contain about the same percentage of ZDP as the oils that solved the camshaft scuffing and wear issues back in the 1950s. (True, they do contain less ZDP than the oils that solved the oil thickening issues in the 1960s, but that's because they now contain high levels of ashless antioxidants not commercially available in the 1960s.)

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 probably take 60 or 70 years for this one to die also.

- Thanks to Bob Olree – GM Powertrain Fuels and Lubricants Group

I added some formatting to the text.

Very interesting about the slight change in phosphorous percentage. How would an individual owner be able to discern the minute difference in percentage?

[Loren]

I can't answer your question about phosphorous levels. Not something I've ever worried about.

When the world suddenly started using 5w30 (and now 0w20) weight oils, though... I did a lot of research on that topic. I grew up in the era where 20w50 Castrol GTX was considered the ultimate engine oil. 5w30 just did not compute!

In particular, I ran across a very well-researched and well-written (but, very long) article a few years ago. Unfortunately, my link to that article is now dead. Ah, but wait... I've managed to find it again: Motor Oil 101

Bear in mind that I'm NOT taking the time to re-read it right now, so don't ask me questions, just read it! Below are some notes I posted to a Miata forum when I initially read this in 2014.

Cliff's notes:

• Oil FLOW is more important than oil PRESSURE. Thinner oil will deliver less pressure, but MORE flow. More flow = better lubrication and more effective cooling of the oil-lubricated parts.
• For daily driving you should be using a 0WXX oil. No ifs, ands or buts. The "0W" = oil that is as thin as possible (but still about 10x as thick as would be optimal) at start-up, which is when most engine wear occurs. Do it.
• The second part of the oil weight number represents it's viscosity at normal engine operating temperature.
• What weight oil should you use? The weight that delivers 10psi per 1,000 rpm in your car at the normal operating temperature. For most daily driven street cars, this will be a 20 or 30 weight oil. You don't need a heavier oil than that unless you're thrashing the car on a race track (not a 60-second autocross run, but a 20+ minute track session) and getting the oil temperature above its street normal range.
• Higher oil temp = thinner oil = lower oil pressure. This might not be bad... remember, lower pressure = more flow... and more flow is good! It's only a problem if your resultant oil pressure at operating temp and RPM is less than 10psi per 1,000 rpm. If you're racing and your oil pressure is consistently lower than it should be, THEN you should be running a heavier oil. If it isn't, then you don't.
• Higher oil pressure does not equal better lubrication. Generally, the opposite is true... lower pressure (as long as it meets the minimum) means better flow, better lubrication, and better cooling.
• Not from this article, but remember that anytime you max out your Miata oil pressure gauge at 90 psi (of course, only 90-94 have a "real" oil pressure gauge from the factory), you're bleeding excess oil pressure (and thus some potential oil volume) through the pressure relief valve. Choose the correct weight of oil to give you adequate pressure and maximum FLOW.
• Also not from this article, but 20 weight oil has been proven (and apparently even listed as acceptable in the Australian owners manual) to work well even in older NA Miatas. Don't be afraid to try a 20 weight... and as mentioned above, there's no reason to NOT make that a 0W20. (only reason to not do it would be if you want to run cheaper conventional oil which may be only available in 5W20) Try it. Worst case, if your engine burns or leaks oil, it might use more of it. Otherwise, it's going to provide the best possible lubrication and engine cooling properties available.
• Also also not from this article... keep in mind that "what the owners manual says" is only relevant to what was commonly commercially available at the time the manual was printed (and/or when the engineers last reviewed it). The owner's manual of an older "inexpensive" car likely wouldn't take synthetic oil into consideration. So, just because your owners manual from 1995 says "use 10W30" doesn't mean that it's not appropriate to use a 0W20 oil. Any 20 weight oil would have been pretty exotic at that time, and 0W probably wasn't even available. Forget the conventional "car guy" wisdom of decades past. Thicker oil is NOT better for your engine. Thinner and preferably synthetic oil is best. As thin as will still get the job done (see above). You'll notice that for long runs of the same car/engine, the oil recommendations will change to match the best commonly available oils... and the trend is for oils to get thinner and thinner as oil technology improves. You want the lightest oil you can get away with, and the NEWEST API spec (currently SM) that you can get, regardless of what your manual says.