The Mazda 3 maintenance schedule does not state the Auto Transmission Fluid Change interval. So, is it determined by inspecting the oil and see whether it needs replacing? The dealer recommends changing at 48k . I know that lot of people recommend changing at 48k. I wonder how they got this number. 48K seems to be a very low mileage to change trans oil. In other cars, I changed at 100k but again they are from different manufacturers.