Paul (Conanski) always recommends using ZDDP additive when you replace the came or rebuild a flat tappet engine. It is recommend at time of build, and at every oil change performed.

My question is, why only after replacement? Why shouldn't, and more importantly haven't, we be doing it on original stock engines? What changes that mandates it? (Just to clarify, this isn't a challenge to the recommendation, it is a desire to understand the why.)

 

When all this came about a few years ago, I spoke with and after discussing this in detail with Ron Eskenderian (yes, Isky Racing Cams), I add one bottle of ZDDP per oil change to my 65 Mustang, and I add 1/3 of a bottle to my mod motors as well (1997 Cougar Sport 4.6 & 2006 Lincoln Mark LT 5.4)- IIRR it is a 9 oz bottle.

 

The ZDDP additive plates the metal with a sacrificial coating that wears down. That is why it is much more important when a new component is installed. Not just for break in, but for use at every oil change. I would also use it in any older engine with a flat tappet camshaft especially if you have a higher lift cam or increased spring pressure. A good one is the Rislone ZDDP additive at O'Reilly and other stores I think. It is under $10.00 per bottle and shows to boost the zinc and phosphorus up to where it was with the older oils.

 

I use a bottle of STP oil treatment every oil change. Viscosity improver, increased thermal stability and ZDDP. Good stuff.

 

Actually no boost in ZDDP Zinc in the STP oil treatment. In fact it will lower your ZDDP level depending on what oil you are using.

 

I would like to see the proof of that, because I'm pretty sure it says "increases ZDDP" right on the bottle.

 

To flip your statement around, I'd like to see proof that STP does what it claims. There are too many snake oil salesmen around, and that includes major companies. They make statements which are technically correct, but wrong in actual real world application.

To see how that can be the case, let's examine STP's claim. If you add STD to an oil with zero ZDDP the claim is in fact a true statement. However, if you add STP to an oil change in conjunction with an oil that has a greater percentage of ZDDP by volume than the STP product, you are in fact reducing the amount of ZDDP in the resulting mix.

The key piece of information missing is what is the percentage of ZDDP by volume for STP and for common motor oils.

 

True, it may not do either.

 

I have tested both the regular STP Oil Treat and the High Mileage product at Polaris Labs. Anyone can buy a product and have it tested fairly inexpensively, under $20 in most cases if you are curious on your own. The STP is between 300 and 500 ppm of Phosphorous and Zinc. Below are a couple of test results on STP. As an FYI regular passenger car motor oil is going to be 600 to 800 ppm of Zinc and Phosphorous. That is todays motor oil, it used to be 1600 to 1800 ppm for the older vehicles. Racing and diesel oil is higher.

 

Therefore, the end result of adding STP to regular passenger car motor oil is to reduce the total amount of ZDDP in the final mixture. The interesting thing is that STP doesn't claim their product increases ZDDP, it only states that it _contains_ ZDDP. As I pointed out in another thread, marketing folks frequently make truthful statements which get interpreted to mean, or lead one to believe, things which are not in fact true.

 

Interesting. So what additives actually increase ZDDP levels?

 

Since ZDDP is the actual additive itself, you would want a product that has a higher percentage of ZDDP per volume of fluid than what ever oil you are using.

Sometimes it's easier to understand a concept when view from an extreme point of view. So let's work it through that way. Start with two jugs with a 50/50 mixture of water and antifreeze in each one. To one jug add add a quart of water with a couple of drops of antifreeze. To the other jug add a quart of antifreeze with a couple drops of water. Which jug has more antifreeze in it? Which jug has higher ratio of antifreeze to water?

The second jug does because what you added to it had a higher concentration of antifreeze than the initial amount of fluid.

 

Other products are much worse like Lucas Oil Stabilizer, it has no Zinc or Phosphorous so it will reduce / dilute what you have in your motor oil significantly.

 

Rislone makes a ZDDP product that bumps up regular oil to around 1500 to 1800 ppm of Zinc and Phosphorous. That product can be found in stores. I know there is a product online called ZDDP Plus which claims the same. Some people also run a racing motor oil as it is higher in ZDDP content.

 

That is exactly correct. The Rislone site show their product would be 13000 to 15000 ppm of Zinc and Phosphorous. It takes that high concentration to boost the levels.