OK I could NOT let this one go.
Let's get a few things straight here and separate fact from fiction and fact from opinion. Here are a few facts.
1. We have an OLDER designed engine. Doesn't matter if you have the M127, M129, or M130. These are fuel-injected variants of the earlier Mercedes-Benz M180 which had a carbureted fuel system. The M180 engine first appeared in 1951 as a 2.2L. Got it? OLD DESIGN.
2. These engines, like others of the era, feature "flat tappets" and not "roller cams" found on later engines from many if not most manufacturers. Do your own research and form your own opinions but the key take-away here is flat tappets feature SLIDING surfaces. Sliding surfaces require more lubrication.
3. Because oil formulations TODAY are different than they were in 1963-1971, data you would find about recommended oils in factory literature really is obsolete. Those oils do not exist any longer. We can only work with what is available today.
Now here comes the well known information that has been around for 20+ years:
1. Late 1980s: The US EPA and auto manufacturers began to reduce the levels of phosphorus (and thus ZDDP) in motor oil to protect the new generation of catalytic converters that were being installed on all new vehicles. API SG Standard (1988): ZDDP levels began to be restricted.
2. Early 2000s: The Crisis Point: This is when the engine rebuilding community began to see widespread problems. API SL Standard (2001) and API SM Standard (2004): These standards severely restricted ZDDP levels (to a maximum of 800 parts per million, or ppm) to ensure long catalytic converter life.
3. The Result: The very low ZDDP in these modern oils, when used in freshly rebuilt engines with flat-tappet (or pushrod) camshafts, led to catastrophic failures—specifically, the rapid wear and destruction of the camshafts and lifters during the critical break-in period.
I didn't make the above up and this isn't my opinion. These are well known and documented facts. So, what was the response? Simple. Engine builders and classic car enthusiasts quickly determined that the lack of ZDDP (a crucial anti-wear additive for metal-to-metal contact areas like flat-tappet cams) was the cause of the failures. They began to formally recommend and require the use of oil additives (like ZDDP supplements) or special high-zinc racing oils for older engines, particularly those with flat-tappet designs (generally pre-1980s or 1990s).
Summarized, the need for ZDDP became an urgent issue for engine builders after the year 2001, when modern oil standards dropped the ZDDP content below the level required for their traditional, high-friction, flat-tappet designs.
Now you be the judge, and do your own research with the technical papers on the subject. There are plenty if you dig deep. Some are available in the SAE database, by Google or other searches, or from the AERA (Engine rebuilders association).
Now let's talk about the moniker "special oil". Nearly every manufacturer of motor oil has an oil designed for older engines like ours. Some of the better known brands that have formulations with higher ZDDP levels (not for catalytic converter cars but older cars like ours) are Valvoline, Amsoil, PennGrade, Driven Oil, Lucas, Royal Purple, Shell Rotella, Mobil Delvac, Mobil 1.
Now let's talk about VISCOSITY. We all know multi-grade oils come with two numbers: the cold or W viscosity followed by the hot or higher number.
Plenty on the subject in any number of places. A 10W-40 typically is rated for the following: A 10W oil is generally suitable for cold-start ambient temperatures down to about −20 C to −25 C (around −4 F to −13 F). I don't know about you but I surely don't use my Pagoda in such freezing temperatures. The 40 weight means it maintains viscosity at 100C or 212F. This is surely a fine choice in viscosity.
But what about a 15W-50? (Note: this is the only choice in street oils in the Mobil 1 line with higher levels of ZDDP). The SAE requires a 15W oil to meet a specific maximum viscosity limit for cold-cranking performance at −20 C (−4 F). This ensures the oil is thin enough to allow the engine to turn over and start in cold weather. Personally I still don't use my Pagoda when it's much below freezing so there's nothing wrong with the 15W as opposed to the 10W, except if you live in and run your car regularly in arctic conditions. What about that 50 rating? Well, that again determines the oil's viscosity at standard operating temperature which is 100 C (212 F). While I'm sure other oils make similar claim, for the oil I use, Mobil 1 15W-50, they say the oil is formulated to withstand the extreme heat of high-RPM engine operation and is designed to protect critical engine parts in temperatures up to 260 C (500 F)
Now a couple of things I can tell you with certainty: our cars run hot. Our engines turn at high RPM. The redline is 6500 RPM, and typical highway cruise in a 4-speed or automatic could very well be either side of 4,000 RPM. That's nearly TWICE what a modern car may operate at.
Another thing to consider about viscosities is the overall condition of your engine. The specifications for oil, even if outdated, were presuming a new car, not one 60 years old with 150,000 miles on it. An engine with a lot of wear might very well benefit from a higher viscosity oil.
So, some facts here. Some places to research. Feel free to formulate your own opinions.
What's MY opinion? When I saw a technical presentation on Mobil 1 in the early 2000s, it sounded good to me, so that's what I chose. Easy to find, and priced like most other synthetics. I've chased their higher ZDDP formulations, and today their oil with the higher ZDDP content happens to be 15W-50. If they had it in 10W-40, I might have chosen that--but they don't. Since I've used Mobil 1 for more than 20 years now, I'm just sticking with it. I guess one would have to have a reason to change--such as reformulation, unavailable, or a much higher price. But, it's been stable in all respects for some time now.
