DF Sales&Marketing
Oil Tech Moderator
In the broadest sense, gas and diesel engine oils have the same anatomy or makeup. They are formulated from the blending of base oils and additives to achieve a set of desired performance characteristics. From this simple definition, we start to diverge when examining the lubricant required performance for each engine type.
emissions and the catalytic converter/dpf system
A catalytic converter is a housing that contains porous metal filler located between the engine and muffler in the exhaust system. Its role is to convert toxic emissions coming from the engine to stable byproducts before they enter the atmosphere. Some of the byproducts of combustion (lead, zinc and phosphorus) can severely cripple the converter’s ability to perform this job. Therein lies the first major difference between the oils. Diesel engine oils have a higher anti-wear (aw) load in the form of zinc dialkyldithiophosphate (zddp). The newer catalytic converters (dpf systems) are designed to be able to deal with this problem, while the gasoline systems are not. This is one of the main reasons you don’t want to use a diesel engine oil in your gasoline engine. If your automobile was built prior to 1975, there is a good chance it does not have a catalytic converter, and thus the above statements do not
apply.
viscosityviscosity is the single most important property of a lubricant.
Typically, diesel engine oil will have a higher viscosity. If we were to put this higher viscosity in a gasoline engine, several problems might arise. The first is heat generation from internal fluid friction. Heat affects the life of an oil. A good rule of thumb is that for every 10-20 degrees c you increase the temperature, you cut the life of the oil in half. The second problem is the low-temperature pumpability of this higher viscosity. During cold starts, the oil May be very thick and difficult for the oil pump to deliver oil to the vital engine components in the lifter valley. This most certainly will lead to premature wear, as the components will be interacting without the benefit of lubrication.
additive levels
Diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts.
So how do you know if an oil has been designed for gasoline or diesel engines? When reading a label, the designation will either start with an “s” (spark ignition) for gasoline engines or a “c” (commercial or compression ignition) for diesel engines. This can be also designated in the “api donut” on the label.
to recap:you will find that some oils meet both the “s” rating for gasoline engines and the “c” rating for diesel engines. To meet the “sn” rating for gasoline engines, you will not find the lower viscosity oils, such as 0w20, 5w20, 5w30, and 10w30 to also carry the “c” specification, which as explained above, and is the diesel specification.
swepco, an exception:
Now, not to confuse you but: the “cj-4" diesel specification in some brands can meet the specifications for both the “sm” and the “sn” gasoline service applications. For example: swepco 308 premium cj-4 plus diesel engine oil meets and exceeds cj-4 diesel specifications, and it also exceeds the api sm, sn specs as well. It is available in an energy saving 5w40, semi-synthetic blend formula as well as 15w40 mineral oil formula.
I do not recommend sm, sn and cj-4 oils for use in engines requiring sl/ci-4 or earlier gasoline and diesel engines. According to the American petroleum institute, they are made to be “backwards compatible” with previous grades, however that does not mean they are the best to use in the older, “historic, high performance, and even “daily drivers” especially for those which have flat tappet cams. In those cases, we highly recommend swepco 306 supreme formula engine oil (api sl/ci-4) for the best protection and longer engine component life.
swepco …solutions to keep it running
emissions and the catalytic converter/dpf system
A catalytic converter is a housing that contains porous metal filler located between the engine and muffler in the exhaust system. Its role is to convert toxic emissions coming from the engine to stable byproducts before they enter the atmosphere. Some of the byproducts of combustion (lead, zinc and phosphorus) can severely cripple the converter’s ability to perform this job. Therein lies the first major difference between the oils. Diesel engine oils have a higher anti-wear (aw) load in the form of zinc dialkyldithiophosphate (zddp). The newer catalytic converters (dpf systems) are designed to be able to deal with this problem, while the gasoline systems are not. This is one of the main reasons you don’t want to use a diesel engine oil in your gasoline engine. If your automobile was built prior to 1975, there is a good chance it does not have a catalytic converter, and thus the above statements do not
apply.
viscosityviscosity is the single most important property of a lubricant.
Typically, diesel engine oil will have a higher viscosity. If we were to put this higher viscosity in a gasoline engine, several problems might arise. The first is heat generation from internal fluid friction. Heat affects the life of an oil. A good rule of thumb is that for every 10-20 degrees c you increase the temperature, you cut the life of the oil in half. The second problem is the low-temperature pumpability of this higher viscosity. During cold starts, the oil May be very thick and difficult for the oil pump to deliver oil to the vital engine components in the lifter valley. This most certainly will lead to premature wear, as the components will be interacting without the benefit of lubrication.
additive levels
Diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts.
So how do you know if an oil has been designed for gasoline or diesel engines? When reading a label, the designation will either start with an “s” (spark ignition) for gasoline engines or a “c” (commercial or compression ignition) for diesel engines. This can be also designated in the “api donut” on the label.
to recap:you will find that some oils meet both the “s” rating for gasoline engines and the “c” rating for diesel engines. To meet the “sn” rating for gasoline engines, you will not find the lower viscosity oils, such as 0w20, 5w20, 5w30, and 10w30 to also carry the “c” specification, which as explained above, and is the diesel specification.
swepco, an exception:
Now, not to confuse you but: the “cj-4" diesel specification in some brands can meet the specifications for both the “sm” and the “sn” gasoline service applications. For example: swepco 308 premium cj-4 plus diesel engine oil meets and exceeds cj-4 diesel specifications, and it also exceeds the api sm, sn specs as well. It is available in an energy saving 5w40, semi-synthetic blend formula as well as 15w40 mineral oil formula.
I do not recommend sm, sn and cj-4 oils for use in engines requiring sl/ci-4 or earlier gasoline and diesel engines. According to the American petroleum institute, they are made to be “backwards compatible” with previous grades, however that does not mean they are the best to use in the older, “historic, high performance, and even “daily drivers” especially for those which have flat tappet cams. In those cases, we highly recommend swepco 306 supreme formula engine oil (api sl/ci-4) for the best protection and longer engine component life.
swepco …solutions to keep it running