Is anyone aware that dexron VI automatic transmission fluid CANNOT be mixed with ANY other transmission fluid? I have heard that this fluid when mixed with another fluid will eventually, over a short period of time, ruin your transmission because of the reaction of the different additives in the two different fluids. Is this true?
From a GM tech bulletin:
Although DEXRON-VI (fig. 1) was introduced into production starting with 2006 model year vehicles (see bulletin 04-07-30-037D), there are still some misunderstandings about it. Here are some facts to help clear up these misunderstandings.
Since GM introduced the first service-fill specification for automatic transmission fluid (ATF) in 1949, it has been necessary periodically to upgrade the specification as part of a continuous improvement strategy. The upgrading process ensures that available service fill fluids are of an appropriate quality for use in transmissions that have been designed around the improved factory fill fluid performance.
IMPORTANT: As with previous upgrades, DEXRON-VI fluids are designed to be backward compatible with earlier transmission hardware. But more important, earlier type fluids are NOT FORWARD COMPATIBLE with transmissions that were designed to use DEXRON-VI.
DEXRON-VI can be used in any proportion in past model vehicles equipped with an automatic transmission, in place of DEXRON-III (for instance, topping off the fluid in the event of a repair or fluid change). DEXRON-VI is also compatible with any former version of DEXRON for use in automatic transmissions.
TIP: Simply topping off the fluid is adequate, but a full drain and replacement is preferred, to obtain the full benefit.
In theory this can cause issues. Let me explain why.
Dexron standards were created by GM. They lost the "Patent" to Dexron-VI in 2006. Now anyone can create their own "Blend" of Dexron-VI. Just like motor oil, you have different chemicals and blends of synthetic oils with different detergents in them; Transmission fluid can presumably be treated the same way. Dexron-VI has a much lower viscosity right out of the bottle than other ATF or Dexron ATF's. When working with an automatic transmission, you have solenoids that actuate the shifting of gears. If the viscosity of the fluid you use is too great, or too low it will cause the transmission to fail because the hydraulic properties and lubricity change. If you mix an oil with another oil and emulsion occurs between the two oil's detergents it can create something of a secondary chemical reaction; You could definitely have an issue if this occured. When you take two chemicals and mix them inside of any moving component with heat, you will have a "science experiment" going on inside your Engine/ Transmission. The additives on Dexron-VI are probably specific to GM transmissions and hence why if you mix it with other fluids, they don't get along.
Just as a side note, Honda/ Acura and Toyota are very much like this. Their specific automatic transmission fluids are designed to work for the transmissions that the engineers built it for. If you put off brand or "General" ATF in the transmissions, they will fail immediately or quite quickly because their properties don't fall within the engineered specification.
2I think you need to re-look at this as it was Dexron-III which they do not have anymore. Dexron-VI is all GM. It was originally assigned to Roy Fewkes who heads GM Fluid Approval Committee. It now belongs to GM Global Technology Operations LLC, which is a subsidiary of GM. It is designed to be completely backwards compatible. I've not heard of there being issues like the OP describes, but have not found any empirical evidence which supports or denies the premise.– Pᴀᴜʟsᴛᴇʀ2 ♦Nov 21, 2015 at 21:43
I stand corrected. Sorry the information about the origin of Dexron was from my memory. The rest of the information that wasn't pertaining to the history of Dexron should be valid information. My answer was more so to support the validity of the OP's concern. To give a perfect answer, a chemist would actually have to test this in a lab =( Nov 22, 2015 at 14:03