ZDDP - The Sequel
| 30 April 2009
I know many of us received a March newsletter that was ravaged by the Post Office but hopefully your copy wasn’t damaged too severely. If you were able to read it, you probably remember the Pony Tricks article about dodging bullets in your vintage Mustang. The last part of the article dealt with rapid camshaft wear related to low levels of ZDDP in API Service SM motor oils, the current API rating. The concern applied only to flat tappet cams (both solid lifters and hydraulics) like those used in the classic engines. Roller tappet cams were safe.
Sometimes I wonder if anyone reads Pony Tricks. Other times, many of you put my mind at ease when you comment about my articles. But damaged newsletters notwithstanding, I’ve never before heard as many comments as I did about the six paragraphs devoted to ZDDP. Many of you asked if reduced ZDDP was a real problem. Others asked what oil to use to get the needed protection. Still others wanted to know if there were additives that could be put in the oil to solve the problem. And so it went.
There was so much interest that I’m devoting this Pony Tricks to a sequel on the subject. I spent several more hours researching ZDDP with much appreciated help from club member Grady Wilson and his son Kevin. Thanks also go out to club member Woody Woodruff for his assistance.
You can blame reduced ZDDP on the Feds, specifically the EPA and, yes, it is a real problem. Actually, the reduction was a good thing from an emissions standpoint because there’s evidence that ZDDP in concentrations greater than 800 ppm slowly poisons catalytic converters. But what’s good for the environment is bad for engines with flat tappets. So if you have a classic pony with a flat tappet cam and no cats to worry about, you should think about ZDDP when you change the engine oil.
Here’s a brief explanation of how ZDDP protects the cam lobes and the bottom of the lifters. Without getting into all of the technical jargon, what you need to remember is that the high pressure and the sliding action of the cam lobe against the lifter displaces the engine oil. With the lack of oil, an alternate source of lubrication is needed to prevent accelerated wear caused by metal to metal contact. ZDDP is the stuff that does that. It dissociates under the pressure and temperature created by the cam against the lifters and bonds itself to the cam lobes creating a protective film that acts as the alternative lubricant. Reduce ZDDP below acceptable levels and you risk destroying your cam. Maintain adequate ZDDP and the cam will live a normal life. Simple as that.
Ok, how much ZDDP do you need? To set the stage, a couple of comments are in order including a quote from my previous article: . . . “in API-SM oils, the anti-wear additive called Zinc Dialkyl Dithio Phosphate, ZDDP for short, has been reduced below the minimum level needed for flat tappet applications.” . . . The concentration in SM oils is . . . “800 parts per million (ppm) . . . whereas the absolute minimum level required by flat-tappet cams is 1000 ppm, 1200 to 1300 ppm is much better.” . . . Some sources suggest that 1600 ppm is more reasonable for street engines.
In many online forums, there’s exhaustive discussion about petroleum based oils that still have enough ZDDP. You’ll see Shell Rotella-T, Valvoline, Kendall, Brad Penn, and other brands mentioned. But most of the comments date back to when the SM transition was taking place. Now it’s safe to say that your local auto supply or Wal-Mart carries only API SM oils for gasoline engines. Some of the containers will say that the SM oil inside is backwards compatible to service SL, SJ, and even SH. But if the additive package satisfies SM, the ZDDP is only 800 ppm, meaning it’s unsuitable for flat tappets.
In my previous article, I mentioned that SL and SJ were still available online but that’s no longer true. The online source is also exhausted.
There are synthetic and synthetic blend oils available with sufficient levels of ZDDP—Roush, Joe Gibbs, Amsoil, Mobil 1, and several others among them. But regardless of brand, if the synthetic is certified to API Service SM, it will have only 800 ppm , meaning it’s no more suitable than the mineral-based oils with 800 ppm. Besides, synthetics might not be the best choice for older engines where design tolerances were greater than those in newer engines, not to mention the still looser clearances related to wear. And in particular, high performance and modified flat tappet engines are better served by mineral oil formulations.
So you have decisions to make. For my part, I prefer to stick to mineral oils that have a good additive package. But is there anything commercially available that doesn’t require adding a can of ZDDP snake oil to the crankcase? I’m not a fan of aftermarket additives so I scoured the Internet as well as the shelves at local stores for a high quality oil with a satisfactory concentration of ZDDP. I already knew there was no point in looking for oils typically used in automotive street engines so let me tell you what I found when I looked for alternates.
Oil for farm machines and lawn care engines was available in API SL (1000 ppm ZDDP) but I couldn’t confirm that any of it was approved for automotive applications. So that idea was scrapped even though the API rating suggested automotive approval.
Some brands of diesel engine oil had adequate ZDDP but other characteristics made them unacceptable. The detergent and dispersant additives required for diesels increase the temperature at which ZDDP dissociates thus making it less effective in gasoline engines. Secondarily, the viscosity was usually higher than desirable for street engines fueled by gasoline. Therefore, my second option was scrapped. By the way, the Internet forums are full of praise for diesel oils as a possible solution for the ZDDP dilemma. Remember that forum comments are frequently opinions that may not be based on facts. Be cautious.
I was striking out so I looked at 4-cycle motorcycle oil. There are some stout oils available for the two wheelers. They have very good properties for the high revving, high output engines, including sufficient ZDDP. But (yeah, there’s a “BUT”) motorcycles have a common sump for the engine and transmission, meaning the oil has to be suitable for the engine, the (wet) clutch, and the transmission. The wet clutch configuration can’t tolerate friction modifiers in the oil because modifiers eventually clog the clutch surface causing slippage and clutch failure. Automotive oils have modifiers so the motorcycle oils weren’t a fit. So much for my third idea.
Wow, this was getting depressing but before throwing in the towel, I decided to look at racing oils to see if they could save the day. After all, racers beat the you know what out of their engines but, costly as they are, they certainly don’t want them to fail. That means they use high quality oil, some of it with a high concentration of ZDDP. But here we go again; the oils weren’t suitable for street use. Usually, the viscosity was too high but there was another important difference. Racing oils lack the aggressive additive packages found in oils formulated for every day use. In general, racers change oil frequently so they don’t need to worry about such things as additives to handle corrosion and other additives to keep contaminants in suspension. Both of those considerations are important on the street so racing oil was another candidate for the “not acceptable” column.
Enough was enough. It was time to turn my thinking to the snake oil additives. As much as I hated the idea, I reluctantly came to the conclusion that the most logical approach was to buy high quality SM oil and add ZDDP to it. That meant the research would begin all over again, only this time the goal would be to identify a good additive.
Break-in oils and additives for seating new cams were readily available from cam manufactures where 1800 to 2000 ppm (even up to 2200) ZDDP was commonly thought to be the right concentration. But additives for the street were harder to sort out. I looked at it this way: The oil generations preceding API SM had 1100 ppm ZDDP or more and when using those oils, a wiped cam was almost unheard of unless the manufacturer had botched the heat treatment. That said, I set my sights on 1200 to 1300 ppm, maybe up to 1400, as a steady diet after break in.
I’m not going to discuss the maze of oil additives on the market but I’ll say that one of the best seemed to be ZDDPlus made by ZPlus, LLC in Burlington, NC. You can get a real education about ZDDP if you take the time to read the information on their website. Of course, some of it’s probably self serving because they’re trying to sell a product. Nevertheless, the presentation is excellent. Check it out and then make up your own mind. You’ll find it at:
http://www.zddplus.com/.
One of the most compelling things on the ZPlus website was a comparison between ZDDPlus and other well known additives including STP, zMax, Marvel Mystery Oil, Castrol Tection, and GM’s discontinued EOS. Another feature was a table that showed how much ZDDPlus to add for a given concentration of ZDDP. That information would let you pick your own level of protection without the usual instruction of adding one can per oil change as many other products tell you to do. Finally, I liked the names of some of the businesses selling the product. It’s marketed by respected concerns such as YearOne and, especially, Eastwood. On the Eastwood site (http://www.eastwoodco.com/) search for ZDDPlus. On the YearOne site (http://www.yearone.com) do the same thing.
I think my parting thought is an obvious conclusion. If you take good care of your flat tappet engine, it will be much less likely to let you down. A major component of that level of care is proper lubrication of the camshaft. In addition to declining performance and eventual failure, a wiped camshaft puts a lot of iron fines into the engine oil. It goes without saying that abrasives like iron fines aren’t good for any part of the engine. So if you kill your cam, you stand a good chance of needing a complete rebuild, not just a new cam and lifters.