Does anyone know if ZDDP by-products poison catalysts? In other words, once the original ZDDP in an oil has been depleted - converted into Zn phosphates and other particles suspended by detergents - can the level of ZDDP in the used oil be increased back to the original concentration of fresh oil without poisoning the catalyst? What if the ZDDP by-products are removed by fine filtration or centrifuge type separation?

Bob K., the only time that I know of that ZDDP or any of its by-products hurt catalysts is if the engine is consuming an abnormal amount of oil. This is not to say that if you have an engine that by design, uses a certain amount of oil between changes that that wouldn't lead to posioning after a period of time.

If the engine doesn't consume any noticeable amount of oil (meaning that from change to change, you do not have to add a drop of make up oil), then the poisioning issue is a non issue, and I would not hesitate to use any oil with a higher level of ZDDP than what the API service designation calls for.

I have an '07 Pilot, which of course, specs a 5w20 viscosity and an SM API rating. I'm currently running a 0w30 racing oil from Maxima, that is SG rated, but contains enough ZDDP to do a half a dozen additive packages of the SM level. I'm not concerned though, as from day one of driving it off of the showroom floor, she hasn't consumed a drop.

According to Wikipedia, the fount of all knowledge, the answer is a definite yes if the oil leaves the engine and gets into the exhaust.

http://en.wikipedia.org/wiki/Catalytic_converter

"Common catalyst poisons are lead, sulfur, zinc, manganese, silicon and phosphorus.

Zinc, phosphorus and sulfur originate from lubricant antiwear additives such as ZDDP; sulfur and manganese primarily originate from fuel impurities or from additives such as Methylcyclopentadienyl Manganese Tricarbonyl (MMT), respectively."

But I would think there would be a big difference in poisoning rates between inorganic ZnPO4/sulfates from spent ZDDP and organometallic Zn-S-P bonds in fresh ZDDP. Just as is the case with the sulfur compounds in jet fuels poisoning the platinum electrodes of fuel cells (use desulfurization beds to protect fuel cell), the electrochemically active sulfur in ZDDP would form sulfide compounds with the platinum surfaces of the catalysts. So if the ZDDP is oxidized, its by-products would not have the capability to react with/poison the catalyst. If this was the case, you could make periodic ZDDP adds to keep wear rates minimal/maximize fuel efficiency at a level friendly to the catalyst over the life of the oil

I think there is a significant temperature difference beween fuel cells and the combustion cylinder and active surface of a catalytic converter. I suspect all the ZDDP is a degradation product by the time it sees the catalyst.

The thermal energy both in the combustion chamber and at the catalytic converter surface should break the organometallic chemical bonds in both normal ZDDP and spent ZDDP. If the S / P / Zn in normal ZDDP causes problems, then the spent ZDDP should also cause problems as well.

The total load of S / P / Zn on the catalyst is probably more important than the chemical form of the elements in the engine oil. As you said, if the spent ZDDP can be physically removed from the oil so it is no longer able to be sent to the catalyst, then the S / P / Zn load after you top up the additive should be within acceptable limits for catalytic converter life.

According to what I've read, ZDDP's detrimental effect on catalysts is far from proven. Moreover, the potential effect depends on the condition of the engine and the quality of the oil. Higher quality oils don't deteriorate in the presence of heat so quickly which means less engine wear and less engine wear reduces the exposure of the cat to combusted oil. For example, I installed my oil 37K miles and 3.75 years ago and I've burned all of about 6 oz during that time. Regardless of the level of ZDDP in the oil (I don't have a clue how much it really has.) I just can't see that my cat would be impacted.

But to protect the engine, you are going to have to disregard OEM recommendations about using the new SM oils with thin viscosities like 0W20 and 5W20. This is a difficult issue because the warranty is an issue for many. Strange how something that was intended to protect the consumer has been turned against them. For my part, I'll choose a really good oil as opposed to the warranty.

http://www.machinerylubrication.com/article_detail.asp?articleid=518

This message has been edited. Last edited by: Houckster,