Engine oils since 2006 and flat tappet cams

Engine oils since 2006 and flat tappet cams

Since 2006, a new designation for petroleum based motor oil was introduced which has no "zinc di-chromate" additive. This additive has been in motor oils for more than 60 years and its anti-wear characteristics have been taken for granted by millions or motorists for generations. This is no longer the case.

The "new" oil has an API Service SM label on the oil bottle regardless of brand. This additive was present in previous motor oils designated SL, SG, and older. Since all modern engines (since at least 1996) have either been equipped with steel camshafts and/or roller lifters, the additive is not required. Also, even in the small amounts present, (approx. .12% by weight) the zinc di-chromate has an adverse effect on a vehicle's catalytic converter when burned in the combustion chamber.

Older vehicle owners beware!
This means most 5W30, 10W30 (regardless of brand name) and many 15W40 oils are lacking this crucial additive. For engines with "flat tappet" cams and lifters, the missing additive means the lifters are slowly but steadily wearing away while you are driving if you are using SM designated engine oils.

For the next few years, some 15W-40 oils (usually labeled "long-life" or "for diesel use") will still contain the zinc di-chromate. Look at the label however! If it says "API service SL or SG" it is safe to use in older engines, but if it says "API service SM" on the label, don’t use it in your pre-1996 engine unless you are running a roller cam or you have and OHC engine with a steel camshaft.

Currently (2008) most HD30 and 20W-50 oils still have the SG designation and still contain the additive, but in the case of the diesel compatible 15W-40 oils this is likely to change within 2 years as the new "clean diesels" come to market. All major brands: Castrol, Pennzoil, Quaker State, Valvoline, and all the major oil companies have adopted the SM designation for motor oil in gasoline engines, so if you have an older vehicle without a steel camshaft, read the labels on the oil you are purchasing.

A few manufacturers such as BMW, Bombardier, and Castrol's Syntec blend, have "long-life" 5W-30 and 10W-30 oils which have a molybdenum additive to provide an additional level of friction protection and these might be a reasonable substitute, however, only time will tell.

Synthetics don't care:
Because synthetic oils are not petroleum oil based, they have different (better) lubricating properties than conventional motor oils. It should be noted that the viscosity of synthetic oils is much lighter and these are generally factory installed and recommended only for engines since the late 1990s. Do not use them in older engines requiring 15W-40 or 20W-50 oils. Most synthetic oils are very low viscosity : 0W-20, 0W-30, 5W-15, 5W-20, 5W30.

The high-performance synthetics like Royal Purple have a viscosity of 10W-30 and have an API Service SL rating so they can be used as a substitute for the old conventional mineral oil based 10W30 oils.