Motor Oil, ZDDP and Yesterdays Engine - Part 1

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Motor Oil, ZDDP and Yesterdays Engine - Part 1

Postby cubguy's dad » Sat Oct 17, 2009 8:38 am

It’s been all over the automotive blogs, chat rooms, discussion groups, and print publications for the last couple of years. The EPA has forced the reduction or elimination of ZDDP (Zinc Dialkyl-Dithio-Phosphate) from engine oil. This is not exactly the whole truth, the EPA mandates that the manufactures warranty the emissions on their autos for 7 years or 80,000 miles and one of these components is the catalytic converter and the exhaust system oxygen sensors. The Zinc is not necessarily the problem but the phosphorus given off by burning of ZDDP is certain death for catalytic converters and O2 sensors. Are there consequences for owners of vintage cars, trucks and tractors or is this just the latest version of ‘the sky is falling’. These were the questions that I looked forward to having answered upon attending the SEMATA conference this Fall 2009.

The SEMATA conference is a Bi-Annual meeting of secondary, post secondary Automotive Instructors along with members of the local SAE society and engineers that work for the Automotive Industry (the GM Tech Center is just down the street). “I know that motor oil is one of those HOT buttons that is always capable of starting a debate amongst us gear heads”. “Most gear heads have a particular brand of oil that they feel is the best, and will debate the merits at length with anyone who doesn’t concur with their opinion. But this latest issue over ZDDP is widespread and touches everyone addicted to motors designed more than 20 years ago”. (Macy) Why do we need ZDDP? This is the question I posed to several engineers and here was the answer. ZDDP is required to reduce wear in the 3 areas of sliding friction commonly found in internal combustion engines. Well, I thought I could name all 3: 1) The lifters and the camshaft 2) The rocker arm to valve contact area 3) The piston to cylinder wall contact area. Well, I was right on the first 2 put the piston to cylinder wall is not sliding friction but more of a shear friction. The third area of sliding friction is the timing chain and gears, I had to think about that but I could see where they were right. How many times have I replaced a timing gear and chain because it was “stretched” (steel does not stretch) but rather the pins and rollers were worn inside the chain along with the gear to roller face. The auto makers have responded to the need to reduce the zinc by designing engines that utilize roller lifters or overhead camshafts, roller rocker arms, timing belts instead of chains these engines have no or very little need for the protection offered by ZDDP.

“Historically, the newest API engine oil designations have always met the performance specifications of the previous ones, and so there was never an issue with using the latest technology motor oil in vintage engines, until now”(Macy). While ZDDP levels have been gradually reduced starting with SG oils in 1988, it is the latest SM designated oil with the nearly total elimination of ZDDP has raised the concerns of all vintage engine enthusiasts who fear the worst for their cams and lifters (Macy) Now I have to admit that I was skeptical of all this doom and gloom talk at first. The problems, which have been reported by several different individuals, concern the rapid wear and almost total destruction of the camshaft and lifters in freshly overhauled engines. “This problem has been blamed on ‘reproduction’ lifters (tappets) which are too ‘soft’ when tested on a Rockwell hardness tester. But now I’m starting to believe that this might have been the first appearance of a lubrication problem, and the new reproduction parts were the quickest and easiest place to lay the blame” (Macy). The cam and lifter breaking period is probably equal to if not more important that piston ring break in or seating. I personally have not experienced this since I use cam and lifter break in lube on new cams and lifters along with a high ZDDP break in oil. Since the benefits of ZDDP are especially important during the break-in period for camshafts and lifters, it makes sense to me that the excessive wear and destruction of parts will show up in recently overhauled engines that have the new SM engine oil installed without using a break in additive or oil, where in years past the engine oil contained enough ZDDP to protect the unwary user (Macy). I believe a fresh engine will see wear in these cam and lifter areas well before we see it in higher mileage engine that is already broke in.

So now that this ZDDP thing could be a real problem, what can we do about it? My question was “How much ZDDP is adequate for a older flat tappet cam engine”? Most engineers agreed that for older engines 1200 PPM (parts per million) zinc is the minimum amount needed for sliding wear protection. Engine oil prior to 2001 had 1200 PPM (parts per million) ZDDP. In 2001 the zinc was reduced to 1000 PPM and in 2005 the zinc levels were reduced to the current 800 PPM. These are typical zinc levels and are not a function of the oils API rating. API does not specify the zinc content just oil performance specifications. “There are a number of possible “fixes”, but deciding on the best one is going to fall back on personal taste, providing even more fodder for oily discussions among motor heads” (Macy). One quick solution that’s been suggested is to use diesel motor oil that contains enough ZDDP to fend off the premature cam & lifter wear. But diesel motor oils carry completely different API ratings which begin with the letter “C”, and they also contain additive packs which were designed for the diesel’s unique characteristics (Macy), and the viscosity ratings of 15w-40 may not be totally appropriate for use in gasoline engines depending on your local climate. You also can't automatically assume that just any diesel oil contains enough ZDDP to provide adequate protection One diesel oil Shell Rotella T 15w-40 (API CJ-4) has about 1200 PPM zinc additive. This is 50% more zinc than the current (API SM CJ-4) engine oils which typically contains about 800 PPM zinc. For many vintage engine owners Shell Rotella T is the oil of choice.

In the wake of all the fears over potential engine damage, oil supplements containing ZDDP are showing up in catalogs and store shelves in a big way. Each will claim to have just what your car needs, and only time will tell if they solve the problem or amount to nothing more than modern day snake oil. Without a performance rating system such as the API designations for oil, there is really no way to substantiate the claims of the manufacturers’ marketing departments until your engine lives another 10,000 miles or so without self destructing. I’m not willing to let my engines be the experimental test bed for these additives, but please be sure to let me know how it all works out in yours (Macy)
Another option is the specialty oils for classic and vintage cars that are starting to appear on the market. All of these list ZDDP as an ingredient, but they all appear to be available only in multi-grade weights (viscosity) such as 10W-30 and 20W-50 so far and are priced at more than I would like to pay.

The fourth and final option is to find some single weight gasoline engine oil that still contains adequate levels of ZDDP and meets an earlier API rating than SM. You’re probably not going to walk into the nearest Auto Zone or Pep Boys and find this oil on the shelf, but it is still available if you do a little bit of digging. You should also know that the days of buying your classic engine oil for under $3.00 a quart are over, but the $5 something it will cost is no different than buying the ‘cheap’ oil and adding a $10 supplement to it.(macy)

I did a quick search on the NAPA auto parts web site (, and with a little luck I found that I could search the engine oils by API ratings, brand, or by weight. You have to get pretty deep into the web site before this becomes available, so I’ll give you a road map to find it. From the NAPA home page, select browse Parts PRO SE Catalog. Then every time you see “Browse by Category”, select the following options in this order; Chemicals & Car Care Products, Oil Grease & Lubricants, Motor Oil – 1Qt/1Liter Universal. From there you’ll be able to search for appropriate vintage car motor oil, and read all of the specs associated with it.(Macy)

I was able to find many straight 30W and 40W oils that could be used, NAPA still carries SL, SJ, and some SH oils in their own NAPA brand, as well as from Pennzoil, Quaker State, and Valvoline. “You may have to get the part numbers from the web site and then have your local NAPA store order a full case (12 qt) for you if they do not carry it, but the peace of mind will more than make up for the small effort required to obtain it” (Macy).
A check of the local NAPA Store also found Valvoline VR1 racing oil with SL, SJ, SH ratings available in both SAE30W and SAE40W on the shelf. “When I looked I was happy to see “ZDDP additive provides tough anti-wear protection” on the outside of the case, and a similar statement on each bottle” (Macy) While this issue and the debate it has caused are far from over, I can rest easier knowing that a solution I’m comfortable with is still available, at least for now (Macy)

The GM zinc additive part number 1052367 is again available, however it is now called engine assembly lube (was called oil additive) and the pint bottle that used to sell for $9.00 is now closer to $24.00 dollars. My local GM dealer has some in stock but he does not sell very much of it anymore (I can see why). There are some on line sources that have it for less I am told.

To sum up the API designations do not necessarily tell the whole story on the ZDDP content of the oil. Some SM oils will still contain some ZDDP, and some of the earlier designations may not contain enough to protect our early design engines. So the bottom line is that you should use the API ratings as a starting point in your search, and then if the oil bottle does not specifically mention ZDDP and the protection it provides for camshafts and lifters, place a call to the tech line shown on most bottles and confirm that you are getting what you think you are (macy)

Macy, Mark. "ZDDP and Me." Macy's Garage. 12052008. Mark Macy, Web. 22 Jan 2010.

Comments and concerns are always welcomed

Experiance is knowing what NOT to do the next time.......
1937 John Deere A (Big John)
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