Using diesel oil...will it damage my catalytic conv?

Long term, it will not help the cat, but will not kill it in a well maintained car.

The Diesel oil is higher in zppd, which is harder on cats.

This does not mean it will kill the cat, like say using leaded fuel would, but its not ideal.

Older cars, I know more about air cooled Porsche 911's than I do 308's, do need zppd. Zppd is good for flat tappet cam shafts, so it is a necessary evil.

Hopefully someone can tell you if the 308's need it.

 

Yes, it will damage the cat. How quickly will depend on the zinc/phos in the oil and the amount of blowby in the engine. If you have to add oil fairly frequently then you can expect cat life to be much shorter. There are a lot of studies re the ZDDP issue. MY PERSONAL CONCLUSION, after reading a lot of data data from oil companies and car/engine manufacturers is that any oil with more than 800PPM of zinc/phos is adequate. Many "normal" oils have that. For example, Mobil 1 0W40, which I now use, contains 1100PPM.

My advice is to do the research and do whatever you are comfortable with. But DON"T use data from somebody trying to sell you an additive - like ZDDP - as part of your decision. Unless you are knowledgeable in oil formulation, leave the additives on the shelf; let the oil engineers blend the oil. If you are convinced that you need the levels of some of the racing oils - around 1800PPM - then I would use them and just replace the cat as needed or remove it for normal operation and replace it when emission inspection is required.

FWIW - the oil you are talking about is much heavier than Ferrari's recommendation, which, as of the mid/late '90s, was 5W40 for all V8 engines, regardless of year.

 

John, have you applied and received your Collector Plates? If so, you do realise you will have gone through Aircare once, so after that, if the cats have suffered, it's not much for you to worry about.

If you're wearing regular plates, then you'll have to go to Aircare every year and that may affect it.

 

If the car is not consuming massive amounts of oil (which, basically ends up going through the exhaust system as vapour), then the cats should last.

 

What's a catalytic converter?