Again, if the oil isn’t getting to the converters then it’s not an issue regardless of the ZDDP level. You stated that the engine burns “no appreciable oil”.
looking for 20w50 with cat friendly ZDDP
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No API rated oil would harm his cats.
However, VR1 is not an API rated oil.
The two above that I copied from the Valvoline website are both API rated oils.
But his question was about Amsoil Premium Protection 20W-50 that he already has.
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BrendanC
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HPL PCEO 20w-50 is what i would use. API SP additive package.
changed annually
changed annually
Interesting, I wonder why the API EOLCS Directory says the 20W-50 has an API SN license? It also says the 10W-30 variety is API SL.
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I don't know.
The PDS for both conventional and synthetic VR1 don't mention any API rating.
Also, I have looked at the conventional jugs at Walmart and there is not API remarks on the label, including the API donut.
And on both oils version say that are not catalytic converter friendly - which means not really a street oil. Also that oil smells horrible.
VR1 20W-50 conventional
https://sharena21.springcm.com/Publ...3793b338/def13d07-04ba-ed11-b81d-48df3793b338
VR1 20W-50 synthetic
https://sharena21.springcm.com/Publ...2d889bd3/3207a799-e29c-e711-9c10-ac162d889bd3
OVERKILL
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In this grade, the API rating doesn't matter in terms of "catalyst protection", as there's no restriction on phosphorous on the non-RC grades.
They are licensed.
It could be. However, it's not written anywhere on the bottle for either grade 10W-30 or 20W-50, including their PDS.
It says Exceeds API service SL but no API donut on the bottle.
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Huh. Maybe you should notify the API because they say it is actually licensed.
This may be the tip of quite a quandary and you’re at the forefront.
The GM 502 and the Mercruiser variant have hydraulic roller cams. No need to worry about getting ZDDP levels of yesteryear. The ZDDP formulation in modern API oils will be more than adequate for this engine. Feel confident with any xW-50 oil.
I'd personally be happy with a 5W-50. Amsoil or HPL would get my vote.
I'd personally be happy with a 5W-50. Amsoil or HPL would get my vote.
I forgot about the Amsoil 5w50, but I am not comfortable running that wide of a spread on these engines. I have been in contact with Amsoil Tech support and their 15w40 SS Diesel oil has SN across the board, while the 5w30 has SN+.
This is Google Gemini from Kendal websites- which indicates I should be looking for at least SN level API.
Recommended API Levels for Catalytic Converter Protection
This is Google Gemini from Kendal websites- which indicates I should be looking for at least SN level API.
Recommended API Levels for Catalytic Converter Protection
- API SP (Current - 2020+): Offers the highest protection, designed to prevent catalytic converter poisoning and reduce phosphorus levels, while also handling Turbocharged Gasoline Direct Injection (TGDI) engine needs.
- API SN Plus (2018-2020): Also highly acceptable, introduced specifically to protect against catalytic converter damage and low-speed pre-ignition (LSPI).
- API SN (2010-2018): Good protection; limited phosphorus to 800 ppm to extend catalyst life.
OVERKILL
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This is why we don't use AI.
The limit of 800ppm on phosphorous was implemented with API SM, this is why ILSAC grades (xW-30 and below) with phosphorous levels above that (like many Euro oils, which have both catalysts and GPF's BTW) are API SL still.
There is ZERO difference in "regulated" catalyst protection between something with API SM and API SP or SQ, they have the SAME LIMITS on phosphorous, in the ILSAC RC grades.
However, as I stated earlier in the thread, the grades you are looking at aren't subject to the RC limits, so they could have 1500ppm of phosphorous and still be API SP or SQ. This is why Mobil 1 Supercar 5W-50 can have 1,100ppm of phosphorous and still be API SP:
Chevron Delo XSP 15w-40. It's SN+ as well as CK4. I did a VOA on the 5w-40 version and the Zn was 729. Run it in my son's GMC Canyon.
Like others have said though, if you're not burning oil then there's not going to be harm to your cats. I run HPL's HDMO CC 5w-40 in my 6.2 gasser and it has Zn of 1247 with no issue.
Overkill- do not blame AI on this, rather you do not agree with the source, and your attachment does not clarify things. Perhaps my question was not comprehensive enough in this case. What I asked Google Gemini was "what API level is required to provide protection for catalytic converters", and I may have cut off API ratings older than SN. So if there is any fault, it is mine. As a software engineer, I am sympathetic to the shortcomings of AI in general- hopefully I can retire before it puts me out of a job 
That said, I did not see Mobil 1 15w50 listed, so I went out searching and found it is SP rated, so that becomes a candidate for me. So far I think there are options with Mobil 1, Chevron, HPL and one other I cannot recall. I did look at Amsoil Dominator 15w50 and that has very high levels of zddp, and Amsoil Tech Support said it was not recommended for my application (marine, cats, normal service intervals).
That said, I did not see Mobil 1 15w50 listed, so I went out searching and found it is SP rated, so that becomes a candidate for me. So far I think there are options with Mobil 1, Chevron, HPL and one other I cannot recall. I did look at Amsoil Dominator 15w50 and that has very high levels of zddp, and Amsoil Tech Support said it was not recommended for my application (marine, cats, normal service intervals).
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I'd keeping using the AMSOIL Premium Protection 20w50. Your trying to fix an issue you yourself admits does not exist which is burning oil. Why not use what's been working good for you?
I do not like the Quicksilver brand, although the 25w50 is a very new product. The 25w40 that is recommended is very expensive for a semi-synthetic blend.
Here is the problem- marine engines run at 50-75% load at cruise, and even the best are going to burn a quart every 50 hrs or less. That is like burning a quart of oil every 3000 miles. From an oil cost perspective, one or two quarts per year at this rate is certainly acceptable, but if the premise of slowly poisoning the cats is correct, I could be in a cat replacement situation every 3-5 years. Retail price of these cats is around $6500 per engine without labor, and I have two engines. So running a high zddp engine oil could be a costly mistake long-term. There has been a lot of "your overthinking it" and perhaps I am, but a mistake for me in this situation could be very costly- thats why I am trying to investigate carefully.
OVERKILL
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My attachment does provide some necessary clarity, let me try to make this simpler:Overkill- do not blame AI on this, rather you do not agree with the source, and your attachment does not clarify things. Perhaps my question was not comprehensive enough in this case. What I asked Google Gemini was "what API level is required to provide protection for catalytic converters", and I may have cut off API ratings older than SN. So if there is any fault, it is mine. As a software engineer, I am sympathetic to the shortcomings of AI in general- hopefully I can retire before it puts me out of a job
That said, I did not see Mobil 1 15w50 listed, so I went out searching and found it is SP rated, so that becomes a candidate for me. So far I think there are options with Mobil 1, Chevron, HPL and one other I cannot recall. I did look at Amsoil Dominator 15w50 and that has very high levels of zddp, and Amsoil Tech Support said it was not recommended for my application (marine, cats, normal service intervals).
- You are concerned about catalyst protection, which, for the RC (Resource Conserving) grades (xW-30 and below) is achieved by restricting the maximum amount of phosphorous to 800ppm.
- Phosphorous, if it makes its way onto the catalyst substrate in sufficient quantity, poisons the catalyst.
- How phosphorous gets onto the catalyst substrate is through oil consumption. Ergo, if your application doesn't meaningfully consume oil, then little phosphorous is making its way into the catalyst.
- The limit on phosphorous is only applied to lighter grades of oil (the Resource Conserving grades, where the focus is on reducing fuel consumption), which are more likely to be consumed, and thus expose the catalyst to phosphorous.
- You are looking at grades (xW-40 and xW-50) that are NOT subject to the limits imposed on the RC grades. There is no limit on phosphorous for the grades you are looking at. This means that the API level of the lubricants you are looking at will have NO BEARING on their catalyst protection level, because they are EXEMPT. This is why the answer from AI is completely off the mark, an API SP or SQ 20W-50 could have DOUBLE the amount of phosphorous present in a 5W-30, and still be compliant, because it's not subject to the same restrictions.
This is why I shared the table from Mobil, which clearly shows that despite having 1,100ppm of phosphorous, Mobil 1 5W-50 is able to be API SP, because the RC designation doesn't apply to the grade. Ergo, your focus on the API level as being indicative to the amount of catalyst protection the product provides is misguided, because that would only be helping you out if you were looking at RC grades, xW-30 and below.
Does that help?
That is a huge help- but steers me back to the original question should not be "what API level" but "what level of phosphorus is harmful given average oil consumption, on a 10w+ or higher oil". But its not an AI error, rather an error in my question. Is this a correct question for my use case ?
I’d also bet that it’s “expensive “ for good reason. It’s a marine specific oil. If you’re going to bat down even the manufacturer’s recommended oil, then don’t post for help then challenge the others here offering suggestions. Catalytic converter issues due to zinc are the result of worn out oil burning junk. Converters never “clogged” due to zinc 25 years ago with well maintained engines (non oil burning).
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