To all, I have a '79 D100 truck, slant six, 3 on tree, 108,000 miles. The EPA forced the removal of Zink from motor oil. Zink, or ZDDP as it is known, is needed in flat tappet motors, and I have read, all motors prior to 1989. I am also a Studebaker fan, and get their publication, Turning Wheels. There have been extensive articles about ruining cams and other parts in Studies, Fords using modern oils. Two products, ZDDP Plus and ZBoost offer enough ZDDP to cover the problem, plus Valvoline VO 20-W50, and a few classic cars oils @ 15-w40. In the June 2010 Turning Wheels Co-operator pages, it mentions that if you have a catalytic converter, you can only use between 600-800 ppm ZDDP, or it will clog up the converter. Most of these additives are between 1200-1600ppm. My questions: Does the slant six in '79 have flat tappets? Do I buy a can of ZDDP Plus and only use half the can as not to cause problems with my converter?
I need an oils change, but won't do one until I find out something.I don't want 20-w 50. I use 10-w40, but am willing to go with 15-w40, if I have to. If it is easier, you can e-mail me at nut661@sbcglobal.net. Thanks.
Tony Keeler, Indianapolis

Hi D100, and welcome to the forum. Take a look at this recent link, apart from showing that we are active participants in discussions, and don't necessary agree on things all the time, there is also some references to ZDDP. The problem related to catalytic converters is the newer demand that the life expectancy of a cat should be a minimum number of miles (don't remember the figure), and there are many additives that will kill the cat over time, zink, phosphorus and sulphur among others. Lead is the biggest killer, that is why we use unleaded fuel today. As our guru Dan says, the API standard states that there is a backward compability for motor oils, and the question is if all the horror stories about low levels of ZDDP are correct. ZDDP will eventually kill your cat over time, but I don't exactly have the impression that the shortened life of a catalyzer because of ZDDP has been a great theme for discussions! I have been in contact with Red Line oil about the contents of ZDDP in their oils, as I don't have a cat in my car! (I have been getting the impression that Red Line is a very expencive oil in USA compared to many others, over here they're ALL priced beyond hilarious!) Anyway, they recommend 10W30 for the slantsix, and they have formulated their synthetic motor oils with sufficient amounts of ZDDP (~1200 ppm). If you live in a climate zone with cold winters, do as many on the forum does, use a good synthetic oil, Mobil1 0W30 or 5W30 seems to be a favorite, or stick to the 10W40 you use now. The synthetic oils have a built-in multigrade effect, remember that the lower, first number describes how the oil behaves when cold, the second how it behaves when hot, so don't be afraid to use an oil starting with 0 or 5, it will just flow better when cold! The matter of oil viscosity and synthetic or not has been a subject in many posts in the forum. I think there is a general concensus that a good synthetic coupled with the correct type of oil filter with an internal standpipe (important!) will make your slantsix happy for years to come. If you use a ZDDP additive, you will have to balance the amount you use against the lifetime of your cat. With no concern for a cat in my car, I'll personally stick to the ZDDP for a while yet, until experience with the new additives can be evaluated over some time and tell me otherwise.

We have an article section that you should read through, and in each section in the forum there is a FAQ (frequently asked questions), where you'll find many links to important subjects. We have a very nice search function that will let you find answers to most of your questions, there are more than 100.000 posts in the engine section alone! Don't hesitate to ask, there is no such thing as a stupid question, but there is of course a lot of stupid answers outside this forum!

Olaf.

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Aspenized

The EPA has NOT forced the removal of "zink" from engine oils. It is actually the phosphorus (Zinc dialkyldithiophosphate - ZDDP) that has been limited to 600-800 ppm in Starburst oils (oils that meet ILSAC GF-4).

Older engines with flat tappets should be using a Heavy Duty Engine Oil instead and these engine oils have plenty of phosphorus for anti-wear. Although the latest API CJ-4 rated oils are limited to 1200 ppm of phosphorus, they typically contain 1000-1200 ppm, which is sufficient for most slant sixes.

All you need in your engine is a 30-grade (0W-30, 5W-30, 10W-30) dual-rated (like API CJ-4/SM) HDEO and skip the additives. The valve spring pressure in OEM valve trains is low enough that Starburst oils should also work fine but HDEOs offer more engine wear protection. There is no need for you to reformulate an API-certified oil.

And welcome from Niagara.

Hi Frank. The 'heavy duty engine oil' and oils that meet the API CJ-4 standard are motor oils for diesel engines. There is a reason these oils are not suitable for petrol engines. The diesel engines produce soot and other hydrocarbon by-products that dictates far more detergents in the motor oil, to keep these particles suspended in the lubricating oil. This in turn can decrease the wear reducing capability of ZDDP by increasing the decomposition temperature of ZDDP. The high detergent content will lower the surface tension of the oil, and can actually increase the wear in bearings in a high rpm (relative to diesel) petrol engines. Diesel engines have bearing surface areas and clearences that take this into consideration. Oil with metallic based detergents will also risk building a deposit layer on valves and in the combustion chamber on a petrol engine.
The API standards will change with the development of more environmentally friendly engines, and the diesel engines and petrol engines in the near future will probably use the same motor oils. Till then, I think it is best to use an engine oil for a petrol engine in our slantsixes. If your oil of choice does not meet your standards, use a ZDDP additive.
Olaf.

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Aspenized

You may want to read this Olafla.

It is true that diesel oils are not recommended for gasoline engines. However, diesels commonly use mixed fleet (or dual-rated) oils and most HDEOs have both a C-rating and a S-rating. If the donut on the label has an API rating like CJ-4/SM or CI-4/SL, it is perfectly suitable for use in both gasoline and diesel engines.

Thank you for the link, Pierre. The input about GM's work to have a global rating for the engine oils in all engine factories underlines what I said about the future. Regarding the use of HDEO by Porsche, I have seen that before in other related matters, but I think they are the exeption rather than the norm. Frank, you are right about the dual-rated oils, but I have seen papers on the subject that still recommends a careful approach to motor oils primarily designed as diesel motor oils when used in petrol engines. The development of better lubricants changes the picture rapidly, so yesterday's reservations may not be valid today. I still prefer an exellent synthetic like Red Line, Royal Purple, Mobil1 or similar for my engines, I think it's cheap insurance, no matter the cost of some quarts of oil a couple of times a year.
Olaf

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Aspenized