In the last year or so loads of information has surfaced regarding engine oil and older flat tappet engines, which includes most engines built prior to the 1990s. Some of the information has been written by oil companies and you can also find different opinions even among the oil companies. This article is not intended to disagree with any of the information in print or recommend a brand name because there is plenty of oil available that has adequate ZDDP. Refer to the API ratings on the container and a description of ratings else where on this website or in one of numerous article written on the subject.

Zinc and Phosphorus (ZDDP) is an anti-wear component necessary in older engines. It has been reduced in most modern engine oils because of EPA standards and the reduced requirement for modern engines. Diesel and racings oils still have large quantities of ZDDP, both of which are formulated for a specific use. Racing oil can be expensive at $15.00 or more a quart.

Eight 4oz oil samples (four brands of oil and four different additives) were sent to Blackstone Laboratories, 415 E. Pettit Ave, Fort Wayne In, Ph 260 744 2380, www.blackstone-labs.com

1. First, to establish a base line, I started with a1980s vintage "Pennzoil" 10W/40 it contained 547 PPM Phosphorus and 716 PPM Zinc. This was one of the popular oils widely available and used in the 80s. It had adequate ZDDP content for flat tappet engines. View Report (PDF)
2. The next oil checked was the older version of "Shell Rotella" T, 15W/40; it contained 1133 PPM Phosphorus and 1276 PPM Zinc. Double the amount of the 1980s Pennzoil. View Report (PDF)
3. Next was the current "Shell Rotella" T, 15W/40. It contained 944 PPM Phosphorus and 1133 PPM Zinc. You can see that the ZDDP content has been slightly reduced, but not enough to worry about because it is still almost double the 1980s vintage oil. View Report (PDF)
4. Next was "Red Line" racing oil, 10W/40 it contained 1968 PPM Phosphorus and 1180 PPM Zinc. Again close to double the 1980s vintage oil. Very good oil for older engines. View Report (PDF)

   The four samples listed below are additives that can be used to boost ZDDP in an oil of your choice. Adding ZDDP could be the most cost effective solution.
   Caution - read all labels on any oil additive.

5. One company ZDDPlus has developed specially formulated for older vehicles. The additive ZDDPlus replaces the zinc and phosphorus which has been reduced in most modern engine oil. An updated analysis reveals that it contains 53980 PPM of phosphorus and 59190 PPM zinc. This product has been developed to protect the collector and classic vehicles engines. ZDDPlus can be added to an oil of your choice and will give more than adequate protection. It comes in 4oz bottles and can be purchased from some Thunderbird parts dealers. I recommend reviewing and read all the tech briefs. Especially interesting is tech brief # 6 which discusses the use of diesel oil and tech brief #8 discusses automotive and oil industry current views. View Original Report (PDF). [ View Updated Report (PDF), showing a significantly higher zinc level.]
6. The next additive analyzed was "Permatex Ultra Slick" it also comes in 4oz bottles and is primarily used as an assembly lube. It can be purchased or ordered from most auto parts stores that sell Permatex products. It contains 527 PPM Phosphorus and 713 PPM Zinc. When mixed with a six quart oil change it boosts the Phosphorus content to 10.76 PPM and the Zinc to 14.56 PPM. Certainly not enough if the basic oil used is low on ZDDP. View Report (PDF)
7. Comp Cam Engine Break-in oil contains 7940 PPM Phosphorus and 639 PPM Zinc. One 15 oz bottle added to a six quart oil change boosts the ZDDP content to 467 PPM Phosphorus and 375 PPM Zinc. Again depending on the basic oil falls short of the 1980s vintage oil. View Report (PDF)
8. "STP" oil treatment in the blue bottle contained 378 PPM Phosphorus and 553 PPM Zinc. One 15oz bottle added to a six quart oil change boosts the ZDDP content to 27.6 Phosphorus and 40.4 PPM Zinc which falls short of the 1980’s vintage oil, depending of course on the ZDDP content of the basic six quarts. View Report (PDF)

If you have a favorite brand of oil or additive that you would like to have checked for ZDDP content by an independent lab I highly recommend you send a sample to Blackstone Laboratories, contact information www.blackstone-labs.com currently a single sample analysis cost $22.50, pre-purchase of six or more $19.00 each.

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Gil