- How much ZDDPlus™ should I add to my oil?
One bottle of ZDDPlus™ will raise the ZDDP concentration level of SL or SM oil to the standards that were in place when SF (or earlier) oil was specified. (SL and SM is the current category available today).

- What if my oil already has some ZDDP?
ZDDP is most effective if the concentration is between 0.18% and 0.2% by weight. Tests have shown that concentrations above this amount, up to as much as several percent, have no effect except to prolong additive life. The current oils available today contain very little ZDDP.

- Can I use ZDDPlus™ with regular or synthetic oils?
Yes, ZDDPlus™ should be compatible with all conventional and synthetic oils intended for automotive use. Virtually all of these current oils have had some amounts of ZDDP for years, and it continues to be decreased in available oils.

- What is the shelf life of ZDDPlus™?
The shelf life of ZDDPlus™ is essentially the same as regular motor oil (many years), as long as a few conditions are met. The temperature should be kept below 120 degrees F and above 0 degrees. You need to keep it sealed until it is mixed with motor oil. ZDDPlus™ has a tendency to absorb moisture, not unlike brake fluid. Absorption of water will degrade its performance, although heating it above 100C until it is not cloudy will restore it.

- When should ZDDPlus™ be added?
Anytime, but the best time is when you get the oil changed. A single 4-oz bottle is the correct concentration for a 4- to 5-quart oil change. This will bring the oil back to SF specifications.

- How long does ZDDPlus™ last?
ZDDPlus™ is a sacrificial additive, meaning that in the process of working, it is depleted. ZDDPlus™ should last the life of a normal oil change as specified by the manufacturer of the car, but attention should be given to the categories of service known as "normal" and "severe" conditions. Severe includes stop-and-go driving and short trips, which result in shortened service life of not only ZDDPlus™, but most of the other additives in the oil.

- Why should ZDDPlus™ not be used in OBD (On Board Diagnostic) cars?
The key ingredient of ZDDPlus™ is ZDDP, which has been known to shorten catalytic converter life. Manufacturers have been redesigning engines for the last decade to minimize the need for ZDDP, in order to lower emission levels. One method is switching over to roller rockers.

- Why not just use diesel rated oils, since they contain higher levels of ZDDP?
Diesel engine requirements are much different than those of gasoline engines. The higher speeds and lower bearing surface-to-power ratios of gasoline engines require oil with higher shear ratings than most diesel oils. Diesels also have higher bearing clearances and that calls for higher viscosity oils. The additional detergents required for soot control actually reduce the effectiveness of added levels of ZDDP found in diesel oils. Also, newer diesel oils beginning in 2007 have greatly reduced their content of ZDDP.

- How does ZDDPlus™ compare to EOS?
Historically, EOS was the most concentrated ZDDP supplement available. It was intended to boost ZDDP levels of oils that already contained EP additives. EOS was packaged in a 16 oz bottle. It also sold for over $10 per bottle. ZDDPlus™ is packaged in a 4 oz bottle and contains TWICE the amount of ZDDP contained in EOS, since it is intended to be used with newer oils that contain little or no ZDDP. In the summer of 2007, EOS was discontinued, making it difficult to find today.

- What about the additives offered by the cam manufacturers?
Some of the "Break-in" or "assembly lubes" offered by cam manufacturers contain marginal amounts of ZDDP while others offer virtually none. In most cases these products are intended for initial run-in and rely primarily on other additives such as MDS (molybdenum disulfide). These products are seldom recommended for continued use and most are intended to be removed before the engines are put into service.

- What about off-the-shelf oil additives?
Automotive engines have always been designed and warranted to work properly with the current available oil at the time of manufacture. There has not been a single off-the-shelf additive shown to perform any beneficial function except financial gain to the additive seller. Unlike other additives that have never been recommended by manufacturers, ZDDPlus™ is a replacement for the long-used component of oil that manufacturers once required, but over the years have been forced to remove from the oil for the benefit of newer cars at the expense of older cars.

- What about the claims of the various additives?
The performance record of ZDDP is well established. The manufacturer of ZDDPlus™ (ZPlus, LLC) makes virtually no claims for ZDDPlus™, EXCEPT that it restores the EP (extreme pressure) function of the oil to the level originally required for your older car. Other additives make far reaching claims. If the claims attributed to most additives were even partially true they would have been part of the standard crankcase fill directly from the manufacturers like ZDDP has been for decades.

- Why haven't I heard more about this problem?
The general public, as a rule, has nothing to be concerned about. The people that need to be concerned are owners of older classic cars and performance cars. After the SF category, the amount of ZDDP has gradually been reduced as each new API category is introduced. Had ZDDP been removed completely after 1988 (SF), the scramble for an alternative would have been a big concern. But, since it happened gradually, the concerns were not so obvious.