Why would ATF transmission fluid turn from light red to dark brown after only 5000 miles of use on a 1996 Toyota Corolla?

Answer 1

just like any other oil heat, dirt, metal on metal will change color. I see its a 96, so it has some miles on it this should be normal. This condition is NOT normal after so few miles. It is an indication that the fluid has overheated and is scorched. There is a fluid cooling malfunction. At this point a fluid change is highly recommended. ATF that turns brown or dark-red may be common but it is NOT normal. ATF should remain light-red as it is when it is new. On older, "high-mileage" transmissions, I think material from worn clutches causes this problem, only when there is a lack of maintenance (fluid changes). Not normal hmmm, so my only question would be when you changed the trans fluid was it a flush or a drain and fill. Flush I can see it will not be normal, but if you just droped the pan and filled 4 quarts or so it WILL change the color.