In order to comply with federal requirements that key emissions control components on new cars such as catalytic converters work (and can be warranted to work) for 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 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 (generally, stuff built before the early-mid 1980s) with flat tappet (vs. roller-type) camshafts is that oils with low ZDDP levels may accelerate wear and even cause premature failure, of flat tappet camshafts. In a nutshell, the ZDDP additives cushion the high pressure point between the lifter crown and the camshaft lobe, acting as an anti-friction, anti-wear barrier. The stuff is especially critical in just-rebuilt engines, during the initial break-in period.
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, almost eight years ago now. Unfortunately, many owners of older cars with flat tappet camshafts are unaware of the changing formulations – and the threat low-ZDDP (and even possibly no ZDDP) oils may represent.
The situation is analogous to the early 1970s, when lead (a lubricant and octane enhancer) began to disappear from gasoline. Engines that had been designed to burn leaded fuel – especially high-performance engines run at high RPMs – suffered 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 or truck older than model year 1980 and the engine is a V-8 or V-6 (or inline six) the odds are virtually 100 percent certain that you have an engine with a flat tappet camshaft.
By the latter half of the ’80s and into the 1990s, roller-style camshafts were becoming the norm – and if you have a car from that era or newer, you are probably safe using currently available oil formulations. 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 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.
What to use?
There are still a few oils on the market that have adequate (pre-2004) levels of ZDDP. These include Shell Rotella T – 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 marketed “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. Royal Purple is good stuff, too – and(at least in my area, Virginia) is usually available at your local major auto parts place.
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.
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. 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, FYI -