I just had my transmission fluid changed in my Buick Lacrosse CXL, they used an STP brand of fluid and said it was Dexron III. I am reading that GM recommends Dexron VI for this car. Is it ok to use DEXRON III? Will it damage my transmission?
Depending on what year your LeCrosse came out will dictate what is specified for your vehicle. GM specified Dexron VI for all 2006-newer automatic vehicles. If yours is a 2005, it should be fine.
With that said, it is absolutely NOT okay to use Dexron III (Dex3 - or any other Dexron) in place of Dexron VI (Dex6) fluid. Dex6 is a high-performance synthetic blend ATF. Dex6 came out in 2006 and can be used in older vehicles which specifies Dex3/4, but the other way around is not true. Dex6 is a bit thinner fluid and will handle heat better than Dex3. Will Dex3 kill your transmission? Probably not, but if you have a warranty on the vehicle, you will surely void the part which covers the transmission. You'll also most likely cause unexpected wear issues in the tranny, especially if the vehicle is used for towing.