Are More Recent API Oils always "Better"?

Question

The API ( American Petroleum Institute ) provides certifications for engine oil.

Such certifications range from SA for 1930's era vehicles up to the current standard SN. The above linked document from the API lists all grades prior to SJ ( introduced in 1997 ) as obsolete.

For SN it lists:

Introduced in October 2010 for 2011 and older vehicles, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85.

I see SJ grade oils still on sale at somewhat cheaper prices, and was wondering if there is any real benefit in using the newer SN oils in a vehicle that was originally designed with the SJ grade oils in mind?

I ask about benefit since it seems to be implied by the above document that the newer grade is reverse compatible with recent, older engines - say anything built in the last 20 years.

Answer 1

SJ is just a new and more developed type of oil, it has more additives and cleaning agents and such. Do you have to buy it for a car designed to take SJ? no. It is completely up to you whether or not you want the SN or the SJ oil. Just whatever you do, do not go any earlier than what your vehicle was designed for!

Answer 2

They are "better" in the engines they were designed for. They would be poor in the engines of 50 years ago with larger clearances and lower temperatures that burned leaded gasoline. As engines have evolved ,the oils ( and API oil tests) have evolved. I used to read test lab oil reports and many of the old additives were aimed at the bromine ( added with the tetra-ethyl lead) and higher sulfur of gasoline of 50 years ago. A present oil would be unsatisfactory under the conditions of 50 years ago.

Answer 3

Actually, when using a different type of engine than for which the recent oils are intended (for example OHV or air cooled engine without catalytic converter as opposed to water-cooled OHC with cat), it may not be such a good idea to use the "latest and greatest" oil.

For example, many old and/or small engines are OHV engines with pushrods and flat tappets. Most cars today have OHC engines (DOHC usually these days), with hydraulic lash adjusters. There is a concern that old oils used to have high levels of phosphorus and zinc additives for flat tappets, but the additives could damage catalytic converters so newer car oils have much lower levels of these additives, which could cause too much wear in those old OHV engines.

So for example I use Stiga 10W30 lawnmower oil in my OHV lawnmower, not a car oil. It would be very hard to find a 10W30 car oil, anyway, so with car oils you would have to substitute a 5W30 oil and it's only SAE30 when hot due to viscosity improvers which degrade eventually, so unless you change the oil yearly like you do with a car, the 5W30 oil could turn to a SAE5 oil or at least something less than SAE30! With 10W30, the risk of having too low viscosity when old oil becomes hot is less, because 10W30 has less viscosity improvers than 5W30.

My OHV generator wants 5W30 oil in climates that can be cold, and I already did the mistake of using a car 5W30 oil once. In the next oil change, I'm going to use 5W30 ATV oil by Honda intended for ATVs that commonly have OHV engines instead of OHC.

The Honda 5W30 ATV oil doesn't have the newest API specifiations (API SH, used in about 1995). Same for Stiga lawnmower oil (API SL, used in about 2003). Newest spec is API SP. I suspect the older oils cause less wear in the valvetrain for OHV engines than more recent car oils.