Hi.
I have a different perspective to many posts here. I have the view that many gallons of good and serviceable oil are replaced unnecessarily, in both engines and transmissions. The major reason that ATF degrades is due to overheating of the fluid. Once the ATF has been overheated it can't recover, so my approach would be to prevent that occurring. The major source of heat input is the torque converter providing torque multiplication from the engine output to the gearbox input, as this process is inefficient, the energy not transferred causes the oil to heat up. So during acceleration, and towing, torque converter action will at its greatest. Later Auto gearboxes have lock up torque converters so when in this state there is 1:1 torque transfer and no slipping to generate heat.
The ATF to engine coolant heat exchanger in the bottom of most radiators can never cool the ATF lower than the coolant temperature. On a hot day towing up a hill the temperature difference and the heat transfer capacity can reduce if the radiator cant dissipate the heat from the coolant, from the additional loads on the cooling systems: hotter engine, AC condenser, warmer ambient temperature to start with.
Instead of wasting money and gallons of oil on frequent oil changes, I would be fitting an additional external ATF cooler. This will assist to keep the ATF below the temperature point where it starts to oxidise, and then cause the other consequential effects: varnish formation, lubricity breakdown, hardening of seals, loss of viscosity and associated loss of clamping force for clutches, then slipping clutches etc. Once these have occurred the damage is done and no amount of frequent oil changes will resolve this.
As to oil that is discoloured (mostly from suspended particles), but not burnt oil, and there is a difference; I am happy to leave it. Automatic transmissions have the advantage over engine oil, in that combustion deposits are not present. Discoloured oil is OK as it's performing the functions that are needed including: lubrication of sliding surfaces, preventing corrosion, dissipation of heat, flushing away worn and liberated particles, hydraulically applying clutches and bands, transferring kinetic energy in the torque converter etc. The filter should be sized to prevent particles that are large enough to cause shuttles, spools and solenoid valves to not operate from being supplied to the galleries.
As to the Aisin advertisement to recommend 2 year / 20,000km changing ATF, well they have a vested commercial interest don't they. There will be a sales and marketing strategy to transfer revenue from someone else's pie graph into the Aisin revenue pie graph and increase their EBIT. I note the advertising flyer has the usual marketing words, like: reduced, longer, better, more responsive, improved feel to try and obtain emotional engagement and buy in. At the end of the day, marketing is marketing, its purpose is to influence behaviour of the target audience.
For those owners that choose many infrequent oil changes, just tell me which oil brand you use, and I will buy shares in that company and encourage you (marketing) to change it even more frequently than you do now, it can't hurt surely?. We both win, you get a warm fuzzy feeling in your stomach and my bank balance increases.
It's the heat that kills the oil's vital properties.
