What oil do you use?

Yes this theory (zinc) is followed by several here. While I have not used it, a lot of responses to threads like this suggest brad penn oils for classic cars.

 

I'd not characterize it as "extra ZDDP", but rather "historically normal levels of ZDDP" -- i.e., it's more that manufacturers have reduced the ZDDP levels in recent times for emission reasons. I've been using a 50~50 mix of Mobil1 10W40 (1000ppm ZDDP IIRC) and 20W50 (1500ppm ZDDP IIRC) to try to keep the ZDDP level up without raising the viscosity too much, but I live in a very warm location. However, I'm no expert, didn't stay in a Holiday Inn, and have no evidence to justify it

 

I use their 20w50 that has 1500ppm zddp IIRC.

 

Red line has sufficient zddp levels, and is widely viewed as a quality oil, with a good base stock. It is full synthetic. All oils certified to SM and later standards have reduced zddp. Redline does not API certify its oils, and so can use whatever formulation it chooses, and it has kept the zddp level to the level appropriate to serve the older engine requirements. eg. the 10w40 that I use (as per the owners manual spec for my Mondial 3.2) Redline does "recommend" that their oil is suitable for SM, SN, SL and CF specifications. But technically, as it is not certified, if you used it in a new car under warranty, a manufacturer might deny a warranty claim for an engine failure based on not using oem specced API certified oil. As I and many others swear by Red line for transaxle gear oil, it is not much of a stretch to believe in Red line as a quality oil.

 

Full Mobil-1 detail is here:
https://mobiloil.com/~/media/amer/us/pvl/files/pdfs/mobil-1-oil-product-specs-guide-2016.pdf

Here is another alternative:
Eastwood ZDDP Oil Additive 4 oz. | Motor Oil Additives | Eastwood

Too much ZDDP will kill your cat.

How much is too much? Using an additive is a guessing game!

Cheers,
Vincenzo
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The general rule of thumb is 1000ppm zddp is sufficient, as with all things more is not necessarily better. 1500ppm probably the max for the benefits, more than that towards 2000ppm and higher downside occurs, being the pitting/spalling of bearings and wear surfaces. It is a bit more complicated in that too much zinc causes the engine problems, and too much phosphorous potentially can damage a cat. Many of the Mobil oils would be fine. Redline I think is at the 1200 to 1300ppm level.

Zddp has been used for more than 50 years, so lots of data on what the right levels are for various applications. Deisel and heavy equipment oils with high pressure and loads remain reliant on this additive, at least for now but as chemistry advances and emissions standards are clamping down on the heavy equipment industry as well, these oils will probably also have reduced levels of zddp in due course as well.

The phosphorous only causes cat problems if the engine is burning oil and gets into a cat, where it coats the catalyst and reduces it effectiveness. That's the main reason oem's were asked to reduce zddp and allows OEM's to meet long emission warranties without worrying about engine wear causing emission failures during their warranty period.

I personally would not want to add zddp additive as going too high is not without consequence. Better to get the specs like the Mobil one chart, and pick an oil that is at the 1000ppm or higher level, and you are good to go.

Redline is a good oil, but pricey, and I no doubt have succumbed to the marketers and have become an oil snob. Like fine wine, whatever makes you feel good as long as the basic speccs are in order.