Well guys and gals, I really hate posting a new thread - however - today I went to my local NAPA store to purchase oil for the CX9. I told him I wanted Royal Purple (which I have used since the 5000 mile mark). He asked me what was the make model, and year of the car. I looked at him like he had fallen off a pumpkin truck. Well, today was my introduction to API classification "SN." He insisted that I could not use the SN designated oil in my 2010 for the following reason: Zinc Dialkydithiophospate (ZDP) is an additive that protects the engine from wear, reduces oxidation, which in itself reduces oil thickening, ring deposits, and varnish. The difficulty is that it reduces catalytic converter life, which the manufacturers are on the hook for until 120,000 miles. (does anybody hear footsteps here?) "SN or GF-5, if you like controls the amount of phosphorous in a couple of different ways, but the big picture is that it reduces engine wear protection in the process (according to this gentleman's training on the subject)
So, I didn't buy Royal Purple, or any other oil. I came home and hit the Internet. One of the first things I learned is that it cost oil companies upwards of $160,000 to have their oil certified. That was an important bit of information, because smaller companies, Royal Purple, for instance, may not have the bucks to pay to have every viscosity in a particular oil tested. I also learned if the oil fails even one part of the test, it has to be completely retested.
Continuing to dig in on this question, confuses the issue. In some otherwise worthy information, backwards compatibility with the older GL-4 is affirmed. However other reputable sites don't mention it. Royal Purple's (RP) web site didn't help much because they have developed an oil that is labeled in such a way to lead one to think the product is approved as an "SN" oil but it's actually not. (Very disappointing coming from a Texas company, whose roots were well founded - even to its name) RP shows two 5W-20 oils, and plainly they state one is for cars still under warranty - duhh? The other is OK for the rest of us with old clunkers? There are other major brands that do not help - one founded by a former USAF pilot - claims their product meets all specifications - but isn't certified. Even Mobil 1 says they meet or exceed - but not that their certified.
Sorry to say I don't have the confidence in my dealership to ask people who may not understand the question as well as even I do, if the new SN is totally backward compatible without damage to internal parts that may not be satisfactorily protected in the long haul. I actually wonder if anyone has that answer yet - but I know there are some great resources on this thread. We all need to know this answer, and even more so going forward.
If anyone is really educated in this field, (IMHO's won't really be too helpful here) please enlighten us.
Before someone jumps up and starts talking about oils always being backward compatible, drift on over to the Petroleum Quality Institute of America's site, and see the graphs of older classifications that will actually harm our engines. I was surprised to read many of them are still in the racks at your automotive store.
So, I didn't buy Royal Purple, or any other oil. I came home and hit the Internet. One of the first things I learned is that it cost oil companies upwards of $160,000 to have their oil certified. That was an important bit of information, because smaller companies, Royal Purple, for instance, may not have the bucks to pay to have every viscosity in a particular oil tested. I also learned if the oil fails even one part of the test, it has to be completely retested.
Continuing to dig in on this question, confuses the issue. In some otherwise worthy information, backwards compatibility with the older GL-4 is affirmed. However other reputable sites don't mention it. Royal Purple's (RP) web site didn't help much because they have developed an oil that is labeled in such a way to lead one to think the product is approved as an "SN" oil but it's actually not. (Very disappointing coming from a Texas company, whose roots were well founded - even to its name) RP shows two 5W-20 oils, and plainly they state one is for cars still under warranty - duhh? The other is OK for the rest of us with old clunkers? There are other major brands that do not help - one founded by a former USAF pilot - claims their product meets all specifications - but isn't certified. Even Mobil 1 says they meet or exceed - but not that their certified.
Sorry to say I don't have the confidence in my dealership to ask people who may not understand the question as well as even I do, if the new SN is totally backward compatible without damage to internal parts that may not be satisfactorily protected in the long haul. I actually wonder if anyone has that answer yet - but I know there are some great resources on this thread. We all need to know this answer, and even more so going forward.
If anyone is really educated in this field, (IMHO's won't really be too helpful here) please enlighten us.
Before someone jumps up and starts talking about oils always being backward compatible, drift on over to the Petroleum Quality Institute of America's site, and see the graphs of older classifications that will actually harm our engines. I was surprised to read many of them are still in the racks at your automotive store.
Last edited:
