Another look at the ZDDP discussion

Question:

I have a 1964 Thunderbird with a 390 cid engine. After the engine started missing terribly, a trip to my mechanic revealed lifters so worn that you could see the springs inside. Obviously, the camshaft was a total loss as well.

My mechanic states that this excessive wear was due mostly to a lack of zinc in the newer oils. The engine was rebuilt and the re-builder recommended adding Lucas TB Plus engine break-in oil with each oil change.

After reading your September article on ZDDP (zinc dialkyl-dithio-phosphate) I am still confused. Is this additive really needed for a rebuilt engine?

More importantly, will putting the additive into the oil do any harm? I am a belt and suspender kind of guy. I only

drive the car during the warmer months, not in our sometimes brutal winters when it is stored in an unheated garage.

Answer:

While I have no doubt that your camshaft was worn to the point where it didn’t work anymore, I question your mechanic’s conclusion that the destruction of the cam was “mostly due to a lack of zinc in newer oils.” How does he know what caused the cam to fail? Lots and lots of camshafts failed long before the quantity of ZDDP in engine oil was dramatically reduced and I’m sure that lots and lots more will fail in the future for reasons unrelated to the diminished amount of ZDDP.

I am certainly not saying that your cam didn’t fail because of the absence of ZDDP because it may have. I am saying that, practically speaking, it’s extremely difficult to know.

If you want some added peace of mind, use a motor oil such as Valvoline Race and Pennzoil GT Performance, which are designed primarily for racing and other heavy duty applications and have about twice the concentration of the zinc-based additive.

If you want to go a step further, put in an additive such as STP, Mechanics Brand Engine Tune Up, or K Mart Super Oil Treatment, all of which contain ZDDP among other things.

As I’ve stated previously, I consider this a waste of time and money in most instances and am comfortable running all of my vintage cars without any oil additives. Where feasible, I do use synthetic oil (Mobil 1) but if I believe a switch to synthetic will lead to leaks I stick with conventional oil, without any additives.

The fact that the engine oil additive business has a long history of deceptive practices, false claims, and trouble with the law does nothing to inspire any confidence in their products in my mind.

(See http://www.ftc.gov/opa/1999/05/duralub2.shtm for a brief explanation of why the Federal Trade Commission went after the manufacturers of several well known engine treatment products.)

In my many years of experience, I have never seen a single engine failure that was actually caused by some shortcoming in a major brand engine oil.