Re: Can't get my wj outta 4lo?
Zinc is used in all engine oils. It is in fact not only Zinc, but Zinc DialkylDithiophosphates or ZDDP. Its an anti wear additive, because it reduces the metal to metal contact of the engine parts. Newer oils have less zinc, because zinc can do harm to the catalytic converter.
Older engines need more Zinc then newer generation engines, so it probably is an advantage for the 4.0 engine, but will reduce the life of the catalytic converter.