Warning: If You Have An Older Vehicle, Choose Your Oil Carefully

If you own an older car, you might want to think twice about the oil you’re using.

In order to comply with federal requirements that key emissions control components on new cars such as catalytic converters last at least 120,000 miles (previously, it was 100,000 miles) automakers have been pushing for reductions in an oil additive known as zinc dialkyl dithio phosphate (ZDDP), which contains phosphorous (as well as zinc and manganese).

The problem for late model emissions-controlled cars is that the phosphorous in ZDDP has been linked with premature catalytic converter failure – or at least, premature loss of converter efficiency.

But the problem for older cars with flat tappet camshafts – which means pretty much all cars built before about the mid-1980s, when roller camshafts began to supplant the flat tappet design – is that oils with low ZDDP levels can cause rapid premature wear, even failure, of flat tappet camshafts. In a nutshell, the ZDDP cushions the high pressure point between the lifter crown and the camshaft lobe, acting as anti-friction, anti-wear barrier.

Running without the ZDDP is almost like running without oil — and with the same results.

Levels of ZDDP in commonly available mainstream motor oils – including big-name brands and high dollar synthetics – have been dropping since the new emissions longevity requirements became effective with the 2004 model year.

Unfortunately, many hobbyists and owners of older cars with flat tappet camshafts are unaware of the changing formulations – and the threat low-ZDDP oils may represent.

The situation is analogous to the days when lead began to disappear from gasoline. Engines that had been designed to burn leaded fuel (especially high-performance engines run at high RPMs) fell victim to premature valve recession caused by the use of unleaded fuel.


The first thing is to determine whether your vehicle is equipped with a flat tappet camshaft.

  • If it’s an American-brand car older than model year 1980 and the engine is either original or has been rebuilt to original specifications, the odds are virtually 100 percent certain that you have a flat tappet camshaft.
  • It’s also very likely you have one if your car is early-mid 1980s.

By the latter half of the ’80s and into the 1990s, roller-style camshafts were becoming the norm – and you are probably safe. But it’s important to be sure.

You won’t find information on the type of camshaft your vehicle has in your owner’s manual.

You’ll need to consult a technical service manual – or simply ask someone who is knowledgeable. The service manager at a dealership for your make/model of car ought to know – or should be able to find out.


There are still a few oils on the market that have adequate levels of ZDDP.

  • Shell Rotella T which is a conventional (mineral-based) oil that was originally formulated for diesel engines. Rotella T still contains 1,200 parts per million ZDDP, according to Shell – which is as much as five times the amount found in other oils. Don’t sweat it that Rotella was/is “for diesels.” It’s also an excellent choice for older, non-emissions controlled engines with flat tappet cams that need their ZDDP. Rotella’s also modestly priced and readily available at most any auto parts store. Shell also markets a synthetic version of Rotella that offers even more protection – as well as longevity and a 5W-40 viscosity for those who operate their vehicles in colder climates. Standard Rotella comes in a heavier 15W-40 blend.
  • Another choice – in a full synthetic – is Amsoil which carries a line of oils with ZDDP in popular viscosities such as 10W-40 and heavier 20W-50.
  • Redline oil is also still fine for older engines with flat tappet cams. Unfortunately, both Amsoil and Redline can be hard to find at your local store; but if you plan ahead, you can order a case from any one of multiple suppliers online and just keep a stash on hand.

Another option is additives.

GM used to sell an over the counter Engine Oil Supplement (EOS) that was just what the doctor ordered – and for only about $12 per bottle. Unfortunately, GM stopped making the stuff and it’s now very hard to find.

Luckily, Competition Cams does offer something similar – its Engine Break-in Oil Additive. Comp cams used to recommend this for initial break-in but now recommends that it be added with the oil at every oil change.

Here’s the skinny from Tech Bulletin 225:

While this additive was originally developed specifically for break-in protection, subsequent testing has proven the durability benefits of its long term use. This special blend of additives promotes proper break-in and protects against premature cam and lifter failure by replacing some of the beneficial ingredients that the oil companies have been required to remove from off the shelf oil.

So there you have it.

If you own an older vehicle, you’d be well-advised to give some thought to your next oil change – and what kind of oil you’ll be pouring into the crankcase.

This is a guest post by automotive columnist Eric Peters, check him out on the web at www.ericpetersautos.com.

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21 Responses to “Warning: If You Have An Older Vehicle, Choose Your Oil Carefully”

  1. John Ricketts says:

    How about Vavoline VR 1 Racing oil which is priced reasonally and is available at autozone,discount,napa and many other locations. This oil is available in most popular weights and has zinc? John

  2. Wayland Smith says:

    I don't know about the zinc content but my 82 302 in an F-100 has well over 500,000 miles without an over haul using VR 1 and STP. Try putting anything else it it, I'll break your arm.

  3. Ron Sheehan says:

    Castrol racing oil 20W40 has what we need too, but it's almost $5.00 a quart

  4. Rae says:

    I don,t quite understand , but is my 89 crown vic flat or roller?

  5. Daniel Taylor says:

    I have a 1977 GMC Vandura with 88,000 miles on it. I used Quaker State 10W40 up until 80,000 miles. Now I use 10W40 Valvoline Max Life.

    Does MaxLife have enough ZDDP to protect my flat tappet camshaft? The MaxLife is suppose to keep seals and gaskets from deteriorating.

    It is like damned if I do, damned if I don't!

  6. jim bourke says:

    I have a 50 Plymouth in super shape. original engine, and have used 30 valvoline for many years. It smokes a little but rings are over 25 years young. Should I be using oir with ZDDP in it. I bet not many of us have ever heard of it;;;;;;;;

  7. How about Synthetic oil, does it have the same issues? Castrol Syntec for example.

  8. Al says:

    Look at the oil bottle. If it has a Starburst symbol that says "for gasoline engines" then the oil is an ILSAC rated rated oil with low ZDP and friction modifiers for improved economy. Fine for the latest model passenger car engines but not fine for older engines. This is true of conventional oils and synthetics. If it has the ILSAC starburst avoid it if you have an older engine or motorcycle. Period.

    The options are very simple. Any of the diesel rated oils such as Rotella (shell), Delo (Chevron) or Delvac (Mobil) are excellent oils that meet all API gasoline and diesel specifications, have much more ZDP in them than the ILSAC rated oils and do NOT have friction modifiers. 15W40 Rotella/Delvac/Delo is readily available in most any store and is an excellent choice for most any engine.

    Cams/lifters are not the only thing to worry about. Distributor drive gears are problematic when ZDP is reduced as well as rocker arm pivots, spur gear oil pumps and older style timing chains. ANY engine older than the early 90's is probably better off using the Rotella or Delo or Delvac.

    Newer engines have been redesigned with roller lifters and roller rockers as well as roller timing chains, gerotor oil pumps and the distributor drive gears are no longer required…so they are perfectly happy with the ILSAC oils rated "for gasoline engines."

  9. Just me says:

    Wrong totally wrong. One of THE reasons motors last longer now is oil improvments. Modern oils will help if you use the proper grade… hands down. As a mater of fact the
    I pull oil samples and test them BEFORE changing oils and can add additives as needed. Also test them on fleets and before buying equipment. I also worked for custom oil blender…Check the specs guys your perpetuating a myth.
    An ASE Master tech… http://www.cadillacforums.com/forums/northstar-pe
    The Starburst Oil Myth — The latest myth promoted by the antique and collector car press says that new Starburst/ API SM engine oils (called Starburst for the shape of the symbol on the container) are bad for older engines because the amount of anti-wear additive in them has been reduced. The anti-wear additive being discussed is zinc dithiophosphate (ZDP).

    Before debunking this myth, we need to look at the history of ZDP usage. For over 60 years, ZDP has been used as an additive in engine oils to provide wear protection and oxidation stability.

    ZDP was first added to engine oil to control copper/lead bearing corrosion. Oils with a phosphorus level in the 0.03% range passed a corrosion test introduced in 1942.

    In the mid-1950s, when the use of high-lift camshafts increased the potential for scuffing and wear, the phosphorus level contributed by ZDP was increased to the 0.08% range.

    In addition, the industry developed a battery of oil tests (called sequences), two of which were valve-train scuffing and wear tests.

    A higher level of ZDP was good for flat-tappet valve-train scuffing and wear, but it turned out that more was not better. Although break-in scuffing was reduced by using more phosphorus, longer-term wear increased when phosphorus rose above 0.14%. And, at about 0.20% phosphorus, the ZDP started attacking the grain boundaries in the iron, resulting in camshaft spalling.

    By the 1970s, increased antioxidancy was needed to protect the oil in high-load engines, which otherwise could thicken to a point where the engine could no longer pump it. Because ZDP was an inexpensive and effective antioxidant, it was used to place the phosphorus level in the 0.10% range.

    However, phosphorus is a poison for exhaust catalysts. So, ZDP levels have been reduced over the last 10-15 years. It's now down to a maximum of 0.08% for Starburst oils. This was supported by the introduction of modern ashless antioxidants that contain no phosphorus.

    Enough history. Let's get back to the myth that Starburst oils are no good for older engines. The argument put forth is that while these oils work perfectly well in modern, gasoline engines equipped with roller camshafts, they will cause catastrophic wear in older engines equipped with flat-tappet camshafts.

    The facts say otherwise.

    Backward compatability was of great importance when the Starburst oil standards were developed by a group of experts from the OEMs, oil companies, and oil additive companies. In addition, multiple oil and additive companies ran no-harm tests on older engines with the new oils; and no problems were uncovered.

    The new Starburst specification contains two valve-train wear tests. All Starburst oil formulations must pass these two tests.

    – Sequence IVA tests for camshaft scuffing and wear using a single overhead camshaft engine with slider finger (not roller) followers.

    – Sequence IIIG evaluates cam and lifter wear using a V6 engine with a flat-tappet system, similar to those used in the 1980s.

    Those who hold onto the myth are ignoring the fact that the new Starburst oils contain about the same percentage of ZDP as the oils that solved the camshaft scuffing and wear issues back in the 1950s. (True, they do contain less ZDP than the oils that solved the oil thickening issues in the 1960s, but that's because they now contain high levels of ashless antioxidants not commercially available in the 1960s.)

    Despite the pains taken in developing special flat-tappet camshaft wear tests that these new oils must pass and the fact that the ZDP level of these new oils is comparable to the level found necessary to protect flat-tappet camshafts in the past, there will still be those who want to believe the myth that new oils will wear out older engines.

    Like other myths before it, history teaches us that it will probably take 60 or 70 years for this one to die also.

    Special thanks to GM's Techlink
    – Thanks to Bob Olree – GM Powertrain Fuels and Lubricants Group

  10. Bob Whitney says:

    I asked and payed for a synthetic oil change at a local shop. How do I know that they used synthetic oil or did they charge me for synthetic and use regular oil?

  11. Still Concerned says:


    Why do the aftermarket cam companies such as Crane and Competition Cam and several oil companies also believe that decreases in the ZDDP level are causing flat tappet cam failures? Quotes from companies availabe per:

    Why are there a growing number of cam/lifter failures among professionally rebuilt vintage street/race engines using tried and true break-in procedures? If it's not due to oil issues, could there have been a metallurgy change in terms of where the cam billets or lifters are now coming from?

  12. Tom Harry says:

    Pace Performance offers a product called Zinc, Mfg. by Les Frickshun Products. Replace one qt. of an SM oil with one qt.
    Les Frickshun Zinc to boost ZDDP level to
    former SJ level (1500 ppm) We use this in
    our engine shop on all of our rebuilds. Or
    contact Les Frickshun Products at:

  13. […] the highest concentrations (at least for the moment) of zddp remaining. Is that luck or wisdom? Warning: If You Have An Older Vehicle, Choose Your Oil Carefully http://www.sae.org/events/pfs/presen…2005spikes.pdf “BACKWARD COMPATIBILITY” IN NEW ENGINE […]

  14. […] a urea injection system) Comp cams makes an additive for flat tappetcam break-in Whats New Warning: If You Have An Older Vehicle, Choose Your Oil Carefully __________________ "Sometimes I wonder whether the world is being run by smart people […]

  15. Steve says:

    I have an 86 iroc z w/305 lg4 engine. I don't know if it has a flat tappet cam or not. I have been told that STP has zdp in it as it's primary anti wear additive. I would like to hear from you about this please. If it is true, STP would solve the zdp deficiency..

    Steve L

  16. I take it these oils are not available at the average gas station?

  17. Tyler says:

    I am a college student doing research for a speech on the removal of zinc from oils and the affect it has on flat rockers and lifters. i keep seeing this SAE Tech Bulletin 770087 but when i go to the website it wants me to pay to look at it. no way am i paying. does anyone know where i can get this bulletin for free?

  18. […] Re: engine break in Interesting read. Warning: If You Have An Older Vehicle, Choose Your Oil Carefully […]

  19. Jerry Garfield says:

    Today’s engine oils are backward compatible. No need for additives or the use of diesel engine oils. Too much ZDDP damages engine bearings. I’m a GM retiree. We published this “Myth” and others, to GM dealers and car clubs were given permission to publish in 2005.