Moreover, when it comes to an engine without full flow filtration - detergents are not your friend - as they are designed to suspend dirt so that it is captured by a filter. Absent a filter one needs non-detergent oil that will deposit dirt in the pan prior to it entering the sump pickup.
Detergent oil will keep your engine cleaner by keeping
sludge from coating the engine. See
BITOG: How does Detergents and Dispersant's work in oil?Detergents serve two principal functions.
First, they lift any deposits from the surfaces from the surfaces of the engine to which they adhere to and then chemically combine to form a barrier film, which keeps the deposits from coming out of suspension and coagulating. Detergents form two kinds of barrier films. On small particles, (generally less than 0.02 microns in size), detergents form an absorbed film which slows down coagulation of the particles. On much larger particles, (ranging from 0.5 to 1.5 microns in size), detergents cause the particle surfaces to acquire an electrical charge of the same sign so they can repel each other.
Secondly, detergents neutralize any acids formed by the combustion of the fuel by chemically reacting with the acids in order to form harmless neutralized chemicals.
Dispersants are polar additives that are used to disperse sludge and soot particles for the purpose of preventing agglomeration, settling and deposits. Dispersant's envelops particles and keep them finely divided. Dispersant's are polymeric and ashless compounds. These compounds are based on long chain hydrocarbons, which are acidified and then neutralized with a compound containing basic nitrogen.
See
Selection of the Right Motor Oil for the Corvair and other Engines (Bottom Line Recommendation 10)
Forget the myth that you can’t put high detergent oils in older engines or engines that have been using poor quality oil. I do it every day! 50% of this market is API SF or lower, frequently without thermostats. They are full of sludge. Some drain plugs come out looking like a cork, with an inch or so of thick sludge on the end. No matter what the engine, I put in a 10W-30 high detergent CI-4 oil and instruct the customer to come back when it thickens up, or the following week if he doesn’t want to check it himself. Once it no longer thickens up quickly we move on to 15W-40 and add a 1200 mile engine cleaner. At the end of that cycle we move to whatever oil the engine should have.
