I have read several threads about the lack of zinc in modern oils and whether it hurts the 2.8 or 2.5 engine. What is the latest opinion on this for a stock engine? Should a zinc additive be used?

some people run Rotella diesel motor oil. It has a lot of additives and grafites... down side is that it will stain the block when it leaks. i don't care about an ultra clean block, so that's what i run..... I'm sure someone on here has some kind of data to suggest I'm either an idiot or a genius. either way, we'll learn something new today.
Ron

the ZDDP is an EP (extreme pressure) lubricant, just like molybdenum in chassis grease for balljoints.

It is useful where there is a high pressure (large force on a small area) metal-on-metal contact.

The highest pressure metal-on-metal interface in the engine is at the cam lobe/lifter of a flat-tappet engine.

I'd be most concerned about having ZDDP in ALL 2.8 engines and 1984 2.5s. 1985-1988 2.5 engines have roller lifters and ZDDP is less important in those applications because there's a rolling element.
That said, I put it in all my OBD1 cars, it's cheap and easy since it's in the STP oil treatment and that stuff is often on sale for less than $3/bottle.

Why not the OBD2 cars? ZDDP (and manganese) poison the catalyst and I hate check engine lights.

Why not the OBD2 cars? ZDDP (and manganese) poison the catalyst and I hate check engine lights.[/QUOTE]

What about catalyst in OBD 1 vehicles? Really that much different?

quote Originally posted by Kevin87FieroGT: What about catalyst in OBD 1 vehicles? Really that much different?

The "catalyst efficiency" code on OBD2 cars is very picky. It will fail on cats that are still working well enough to easily pass a tailpipe test.

I don't know if there's any data on how much difference it really makes to their life span, but healthy levels of ZDDP used to be standard in the 80s and 90s, and catalysts lived long enough. The cat for a Fiero isn't very expensive as long as it lasts a decent number of years. But on a newer car, they're horrific.
Nowadays the EPA requires manufacturers to guarantee the cat for something like 100-150K miles. That was a good motivation to cut back ZDDP which they no longer needed as much of.
Just don't go crazy with it and you should be fine. In the 80s/90s it used to be around 1200-1500ppm Phosphorus. Not that I'm saying we need 1500, but it was common back then. If we judge against that standard, it would take real effort to find anything that's too high. Most modern oil can't go over 800ppm. Valvoline VR1 is 1300ppm, and I think Quaker State Defy is around 1000-1200 depending on viscosity. I don't know the number on Rotella but it's fine, it's not anything crazy.

I don't suppose ZDDP plays any role in making a catalyst break up into pieces, does it? I'm assuming that's caused by overheating. A bad cat is one thing, but blowing chunks through the muffler ticks me off.

[This message has been edited by armos (edited 02-12-2014).]

quote Originally posted by f85gtron: some people run Rotella diesel motor oil. It has a lot of additives and grafites... down side is that it will stain the block when it leaks. i don't care about an ultra clean block, so that's what i run..... I'm sure someone on here has some kind of data to suggest I'm either an idiot or a genius. either way, we'll learn something new today. Ron

I use Rotella in are MX race bikes where the 4-stroke bike rev up over 10k rpms and it works great. So I'm sure it would be great for the car. In fact Fiero will get it the next oil change (unless I'm to lazy like last time and just go to a quick lube, lol.)

Quaker State high mileage oil claims to have zinc, irrc.