Since you cannot completly drain the old fluid out I think it is not a good idea to mix the synthetic with the old Dexron. If you did a rebuild and started off with all synthetic there may be some benefits but to not be able to remove all of the old fluid and only add a small amount of synthetic probably isn't recomended by the maker of the synthetic oil. If the old fluid isn't burnt or discolored then it is best to just stay with Dexron. What is most important is not to overfill or underfill and NEVER overheat. Clean out any friction materiel and inspect for metal in the sludge and the chip magnet. Remember on an automatic you also have to check the gear oil level in the final drive. If you have enough miles on the car you may want to change that. David Teitelbaum vin 10757 --- In dmcnews@xxxx, Delorean17@xxxx wrote: > Hi List, > I am going to change my trans fluid soon and I was curious to know if > putting 100% synthetic Amsoil trans fluid in it will hurt anything. It is > fairly pricey but I have been very happy with their stuff in my other cars. > Before I go ahead and do this I just wanted to make sure I am not going to > hurt it. > > Thanks > > David > Grand Rapids, MI