Isiy ok to mixed transmission Fluid - regular & synthetic on 2004 Toyota 4Runner

Hi, My Mechanic used four QTs of Coastal DexMerc Auto transmission Fluid and two QTs Coastal Synthetic Blend Mercon V Auto Trans Fluid when he serviced the transmission in my 4Runner 2004 (6 Cyl) SUV. Wll that cause problems to my transmission? I have always heard you should not mix regular with synthetic. Please advice... Thanks

by in Tucson, AZ on May 23, 2010
1 answer
ANSWER by on May 23, 2010
This was not a 'smooth move' by your mechanic. Why did he do this, did he run out of one? I would ask for the correct fluid and all quarts of that fluid ASAP. Synthetic fluid has a different chemistry. Most modern vehicle REQUIRE a synthetic ATF, so I would say that your mechanic preformed poorly! Most of the literature requires that Toyota factory type IV fluid be used in your truck. When I service a Transmission like this, I ALWAYS use the factory fluid!! For example, if you don't use Honda fluid on a Honda, the seals crack and you have to completely OVERHAUL the transmission. I view a Toyota in the same class. If a factory puts out its own trans fluid, they do it for a very good reason, that being, the component requires a special fluid!!