The reason you follow the manufacturers recommendations is to keep the manufacturers warranty. If you are not concerned with Ford's warranty any longer than do not worry about it.

Another user (NoMo) made an interesting statement about Amsoil in another thread that caused me to do additional investigation. Thanks to NoMo for putting me on this trail. Please follow me on this logic because it's important.

Amsoil makes four motor oils they claim are for use in Diesel engines. Three are fully synthetic (30 weight, 5W-30, and 15W-40) and one is a synthetic blend (15W-40). Let's forget about the 30 weight oil and the synthetic blend oil for this conversation, and we'll concentrate on the fully synthetic oils that some here are using.

I will post verbatim from some sections of the 2002 Duramax Diesel Supplement page 6-18 which is titled "What Kind of Engine Oil to Use". Next to a graphic of the API service doughnut is the following statement: "This donught-shaped logo (symbol) is used on most oil containers to help you select the correct oil. It means that the oil has been certified by the American Petroleum Institute. You should look for this on the oil container, and use only those oils that display the logo." There is also a NOTICE that says "If you use oils that don't have one of these designations either CH-4 or CG-4, you can cause engine damage which is not covered by your warranty." You can read it yourself in your own manual for verification.

These are clear statements! Use only the proper API Certified oil or your warranty won't cover any damage.

I called the American Petroleum Institute to find out if Amsoil fully synthetic diesel oil is API approved (I talked to Kathy in the Motor Oils Division). I was told that Amsoil has been issued API License Number 0995 but that DOES NOT cover any of their multi-grade fully synthetic diesel oils. NoMo pointed out that the Amsoil does not carry the API starburst or donught-shaped logo.

Amsoil fully synthetic diesel oils are not API approved and are not approved for the use in your Duramax. API told me that all oils submitted for certification are tested by both their labs and an independent lab before a license for certification is granted. They would not tell me if Amsoil has submitted their oils and they failed, or if they have never submitted their oils for testing.

Amsoil claims that their synthetic diesel oils are "Recommended for Applications Requiring the Following Specifications:" and list various API ratings, but that is not the same a being API Certified, and not approved for the Duramax. They are telling you that you should beleive them that it meets API specifications, but we really don't know if it does or not. We do know it's not Certified as such. The only API Certified engine oils listed under the Amsoil license are the XL-7500 and PCO (synthetic blend) motor oils.

API Licensing - Passenger Cars - What is it?

An API (American Petroleum Institute) license indicates that a specific motor oil formulation has passed the minimum performance standards as defined by a series of laboratory bench, physical, chemical and engine tests. These tests were selected and minimum performance standards were set by the API Lubricants Committee to address specific areas such as engine wear, deposits, fuel economy, emissions, etc. The committee is comprised of representatives from automobile, oil and additive companies.

Costs

The cost for running a test program for a single passenger car motor oil formulation is from $125,000 to $300,000, depending on if the formula passes the tests the first time through or requires multiple test runs or formula modifications to achieve a passing average. (That amount goes to $275,000 to $500,000 for a Heavy Duty Diesel licensing program on a specific formula.) Once that testing is complete and the formula has passed all of the minimum requirements, it can be licensed for $825 per year for non-members and $625 per year for members. There is also a small royalty fee per gallon sold for all gallons over one million. The length of time between new specifications is now approximately 2 to 3 years, which does not allow a great deal of time to recover testing costs.

Who Licenses What Formulas?

Additive companies, such as Lubrizol, Ethyl,, Infinium and Oronite, develop licensed formulas that they offer to oil companies to re-license. It is inexpensive to re-license one of these formulas, and the majority of oil companies choose to do this to avoid the costs associated with testing. This, however, tends to commoditize the market. The same chemistry is being sold under many brand names. Most of the major oil companies do have their own proprietary formulas developed, tested and licensed. All of AMSOIL INC.'s lubricant formulas are unique and proprietary.

Flexibility In Manufacturing An API Licensed Formula

API licensing was originally developed for mineral based oils, and it affords these oils more flexibility than synthetic oils.

Mineral oils comprised of group I and Group II petroleum basestocks may use a simple program called basestock interchange for added flexibility in manufacturing and purchasing. Interchange means that by completing the proper paperwork and running a few minor engine tests an oil company can choose to buy these petroleum basestocks from many different suppliers. This ensures adequate supply and competitive pricing. However, basestock interchange for Group III and V synthetic basestocks is not allowed. For example, if a formula was tested with an ester (Group V) basestock from a specific supplier, then anyone blending that formula must buy only that supplier's ester. Complete engine testing would need to be performed on the formula using another supplier's ester before an oil company could buy it from that alternative supplier. This additional testing is normally not performed because of the associated costs. This inflexibility makes it very difficult for synthetic lubricant manufacturers to negotiate prices with synthetic basestock suppliers.

There is also something called viscosity grade read-across. Fortunately, this applies to both petroleum and synthetic basestocks although the better cold temperature performance of synthetics makes it more difficult to achieve in some situations. (That's another whole story.) What this means is that if you properly formulate the lubricant for which you have run all of the API tests, there are guidelines that allow you to use that same formula to make 0W-30, 5W-30, 10W-30, etc. viscosity motor oil.

Finally, there is a rule for substitutions in the CMA (Chemical Manufacturers Association) code of practice that allows a small degree of flexibility for all formulas. It allows a company to change the percentages of components in the formula by varying amounts from the original formula with limited testing and paperwork requirements. For example, if the licensed formula used 10% of a certain V.I. improver, you would have the ability to utilize from 9% to 11% of the same V.I. improver for your formula.

Key Limitations For API Licensed Formulas

Phosphorous content - .10% maximum
(API SL; 0W-20, 5W-20, 0W-30, 5W-30, 10W-30 viscosity grades, only)

NOACK volatility - 15% maximum



The prevalent sources of phosphorous in motor oils are additives called zinc dithiophosphates (ZDTPs). Currently, these versatile additives act as oxidation/corrosion inhibitors and aid in the ability of a lubricant to reduce wear. The automobile manufacturers, however, have demanded that lubricants contain a maximum of only .10% phosphorous. Their reason is that some manufacturers believe that higher phosphorous content levels will poison the catalytic converters on their cars before they reach 150,000 miles, which is the number of miles that their vehicles will be required to pass EPA emission standards. There has not been total agreement within the automotive and lubrication industry about whether phosphorous levels over .10% actually do harm catalytic converters in the long run. What they have failed to make allowances for is the NOACK volatility of an oil.

The maximum allowable NOACK volatility percentage for the new SL/GF-3 passenger car motor oil specification is 15%. Most of AMSOIL motor oils are in the 5% to 8% NOACK volatility range. Studies have shown there is a correlation between NOACK volatility, oil consumption and the amount of phosphorous from motor oil that will end up in the exhaust gasses. Therefore, oils with higher levels of phosphorous but with low volatility, such as AMSOIL motor oils, present no more risk to catalytic converters than low phosphorous oils with higher NOACK volatility. This has also been demonstrated for years in actual application through state mandated exhaust gas testing on our Dealers' and customers' high mileage vehicles using AMSOIL synthetic motor oils. State inspectors are continually amazed at the low emissions levels generated by vehicles using AMSOIL products. So much for poisoning catalytic converters.

AMSOIL INC. has determined that the reduced wear and extended drain intervals achievable with phosphorous levels higher than the API limit of .10% are real benefits for the consumer, and pose no risk to catalytic converters. AMSOIL motor oils, except for the API licensed XL-7500 5W-30 and 10W-30 viscosity grades, all have greater than .10% phosphorous levels, and therefore, cannot be API licensed.

Why Some AMSOIL Synthetic Motor Oils Are API Licensed And Some Are Not

1. Full API licensing puts AMSOIL INC. in an inflexible position. Not only would we find it necessary to buy formula components from specific vendors and be at the mercy of their pricing, we would not be able to make any major improvements to the lubricant formulas for 2 to 3 years, without new testing and the associated costs. To solve this problem, the API must establish basestock interchange guidelines for synthetic basestocks just as they have for other basestocks, as well as develop interchange guidelines for other components too.

2. Full API licensing would impose strict phosphorous limitations on our motor oils. This limitation is the main reason most AMSOIL motor oils are not API licensed. AMSOIL INC. currently disagrees with this limitation and feels strongly that the reduced wear and longer oil and additive life achieved through higher levels of properly balanced phosphorous content is more important than the arbitrary API phosphorous limit that does not give any consideration to the NOACK volatility level of an oil. When chemistry is developed that will provide superior engine wear protection with reduced phosphorous levels, or Noack volatility considerations are put in place, then the phosphorous level will become a non-issue.