Regarding the Use of ATF as a so-called engine cleaner:
In the early days of ATF when it contained an ester called, "Sperm Whale Oil," and a naphthenic base oil, Group I mineral motor oils at the same time had little or no detergency additive.
When added to the poor Group I mineral base oil it did do some cleaning because it 1) was thinner than the old motor oil, 2) the naphthenic base oil and Sperm Whale Oil made a it a mild cleaner.
Today's ATF has only 4.2% of the detergency as do current motor oils and little to no naphthenics. Saying it differently, current Motor Oils average 24 times the detergency of current ATF's.
Naphthenic base oils have poor Viscosity Indices and tend to oxidize quicker than do Group II through IV base oils, which is why Naphthenics are rarely used, except as "solvers," and only in very low amounts.
Naphthenics HAD to be used back then in ATF's in order to bring the Sperm Whale OIL into solution.
Furthermore today's Synthenic ATF's contain less than 5% of any type of ester and average about 1%, depending on the formulation.
Sperm Whale Oil was actually the "Liquid Waxy Ester" derived from the spermaceti organ of the Whale's head.
Liquid Wax Esters today are synthesized (reacted) using bio-acids and selected alcohols.
If you need an effective engine cleaner due to sludge buildup or ring coking, use any of the current products containing a mix of solvents and run up to temp, shut off engine, and then change oil and filter.
LCD Inc, LC20, is a good slow engine cleaner that both softens and "solubilizes" carbon.