does any one know if Dexron iii can be replaced with Dexron iii h?

 

Yes. All of the Dexron fluids are backwards compatible. The current Dexron is VI, which can also be used in place of III. With the Dexron fluids, you can go with a higher humber, just not a lower number. Back in the days of Dexron III, they started adding letters to the end just meaning an improved fluid. They are all compatible, as long as you don't use a number less than what OEN calls for. (Don't use Dexron III if the vehicle calls for Dexron VI)

 

Try to get a name brand Dexron though like Valvoline... Some of the store bought brands do not make it quite right. Dexron IV can be used in P38 rovers, but if you can find Dexron III, it is preferable. I had Dexron IV in mine and it caused grinding noises in the transmission (later it became apparent that it was a slurping noise from the pump). Putting Dexron III into it made the noise go away.

 

Dexron VI is a synthetic blend, while III is conventional. GM says VI is twice as durable as previous versions, etc, but I still run Valvoline Dexron III in mine.

For whatever reason, GM skipped over Dexron IV and V and went straight from III to VI. There is a Mercon V (Ford) and a Type IV (Toyota) though.