I have a 2004 Toyota Avalon XLS, automatic transmission with 166k on it. I have never swapped out the transmission fluid at sound advice from loved ones with self-maintained vehicles that have aged well over the decades. I recently noticed the shifting doing two things at a frequency of about once per week: (1) not engaging as quickly as it used to when changing, and (2) getting stuck and revving up the RPMs unexpectedly. So, I figured it was time for a change (NOT a flush). My boyfriend lovingly offered to do the job for me, as he had done it before on his Previa without a problem. I did not hover over him and only came into the garage when he said the job was done. We started up the car and it would not shift into gear. We ran the car for maybe about 10 minutes, occasionally shifting through the gears. Still, no motion in the ocean. We took a step back and I asked him to show me what he did. When we got to the step of him adding the transmission fluid, he showed me that he funneled all 4 quarts of transmission fluid into where the engine oil goes! SO…we ran the car with an OVERFILLED engine oil compartment (likely at a 1:1 oil:ATF ratio) and an EMPTY transmission.
What kind of damage am I looking at due to the empty transmission and overfilled oil?
How best do we clean the oil compartment? Change it several times in short succession? Use an additive?
Thanks all for your help!