Zinc Anti-Wear Agent Missing From Modern Motor Oil

Engine oils today are not the same as they were a few short years ago. If you have an antique or classic vehicle be careful which type of engine oil you use. The brand does not matter… it is the additives or lack thereof that you need to be aware of.

Most engines built in the 1970's… and before, have a flat tappet valve train. That means the bottom of the lifter wears on the camshaft lobe and the two surfaces are flat, (for the sake of this discussion) creating a common wear surface.

By contrast…Modern engines and some high performance engines use what are called roller tappets, the bottom of the lifter has a wheel that rolls against the camshaft lobe surface. Both surfaces are hardened in the modern engine applications so there is less wear and less friction.

Prior to the introduction of catalytic converters and emission rules… engine oil contained and additive package made up in part of zinc dialkyl dithio phosphate commonly referred to as the "Zinc" additive. Zinc was included as an engine oil additive to provide additional protection, to the bottom of the lifters, lifter bores, camshaft lobes, and between rod bearings and main bearings. Engine oils typically contained 1000 ppm of zinc additive by volume.

Zinc as an engine oil additive has been around since the 1930's and was originally developed to prevent damage to rod and main bearings from the coolant and engine oil lubricants of the day. Early day engine oil would break down and turn to carbon under high heat conditions. Engines also did not seal well in those days and cooling system leaks into the crankcase from leaking head gaskets were common. The Zinc additive provided an extra margin of wear protection.

In the early 1980's when catalytic converters became a required accessory the EPA determined that the Zinc additive package in the engine oil was causing the catalytic converters to fail early due to phosphate contamination, which was part of the zinc additive. Thus began the reduction of zinc anti-wear package in modern engine oil. Modern engine oil is far superior to the engine oil available prior to the 1970's. Engine technology has also greatly advanced within the last ten years eliminating some of the internal wear issues the older engines had. However….most flat tappet engines were built using the prevailing technology of the day.

Meanwhile…
With the introduction of the EPA 100,000-mile emission warranty requirement in 2004, the zinc additive package quietly disappeared from automotive engine oil altogether. That helped to extend the life of the catalytic converter and related emission accessories as required by the EPA. It was not a good deal for older flat tappet engines.

The "new" engine oil became known as "energy conserving engine oil." Our plan "B" of using diesel engine oils such as "Rotella", because of the zinc additive still being present, is in trouble also. All of the diesel truck oils are reducing or eliminating completely the zinc additive package due in part to the more strict emission standards.

Older antique engines that have a flat tappet valve train still need the wear protection that the Zinc additive provides. Any rebuilt engine definitely needs the zinc additive to protect the camshaft and lifters from scoring and scuffing. This is especially true if you are rebuilding an older engine. You can ruin a new cam and lifters in 60 seconds or less without the proper assembly lube and zinc additive included in the engine oil.

You can put back the Zinc additive package when you do a regular oil change and that will allow you to use the modern energy conserving oils in your older engine. You can order a Zinc replacement additive package from the Parts Counter pages.

The lesson here is do not buy energy conserving engine oil for you antique or classic car engine unless you also buy and use a zinc additive. Do your homework… and real labels carefully. Not all zinc additives will give you enough protection. Be sure ALL of the original ingredients are included in the Zinc additive you buy. See the parts counter pages for the complete list.

1000 ppm is the minimum acceptable level. You can tell if the ZDDP has been lowered or removed from the engine oil in question by the Service Designation on the label of the oil container. If you see Service SL or lower (SI, SJ, SK is lower) then ZDDP levels should be 1000 PPM or more. If you see Service SM or higher (SN, SO, SP, is higher) then the ZDDP additive package has been removed to meet current EPA standards.