I bought a used 4L60E with 80k miles on it from a friend and have drained all of the old fluid from it. I intend to install it on my truck which I am putting back to stock. It will be my daily driver for a short period of time.

Would it be okay to refill it with Dexron VI fluid? I have a ton of this fluid sitting on the shelf and would like to put it to good use.

I believe GM now recommends using Dexron VI in all new and old transmissions to supersede Dexron III.

Thoughts?

 

Using the newer fluid should be OK. Using the older fluid when dextron 6 is required is a no no.

 

Should be fine. Dex 6 is the replacement. It's used in place of Dex 3 now.

How ever it is not backward compatible. You're not supposed to go from 6 back to 3.

 

Cheap Walmart dextronIII is want my builder always suggests to us.

 

He asked if the Dex6 he already had laying around was ok to use in a used transmission. Not what he should go out and purchase.

Dexron 6 is Gm's replacement fluid for Dexron III and will work just fine. Especially when he already has it.

 

80k on it shouldn't be a problem. This issue is more in changing the fluid at all than it is changing to Dexron VI. Old ATF loses its detergent properties over time. The detergents keep things clean by preventing deposits. After many heat cycles, or miles, or age, the fluid gets to a point where suspended particulates in it begin to deposit themselves into all the corners and cavities inside the valve body. That generally doesn't cause any problems because those chunks of deposit build-up stay put with the old fluid. However, when fresh ATF is introduced with full-strength detergents, it can cause those deposits to break loose and create fluid blockages. With only 80k on it this is not likely to be a problem, just be aware that this is always a possibility when fully replacing the ATF in any automatic.

 

Well I put the transmission in this weekend and topped it off with 11.5 quarts of NAPA Dexron VI and it seems to be working fine. The old fluid that came out of it was exceptionally clean, and there was very little "sludge" in the bottom of the pan.

 

This makes sense! Thank you!

 

So this would be a good reason as to why you should regularly change the ATF? how long of a time period is referenced by saying "old atf loses its detergent properties over time"?

thank
_Zblee

 

This is one of those subjects where you'll get five different opinions from five different people you ask. One of the specification targets with Dexron-VI was extending the service interval enough to "seal" it in the transmission. Some don't even have a dipstick anymore. I think for every truck it's going to be different depending on how its driven and what work has been done to it. Even the pan capacity is a factor. Torque converters with higher stall rpm will heat cycle the fluid more severely where performance clutch pack and recalibrated valve bodies will reduce heat and clutch material degradation. Fluid that has been overheated is less pink and more brown. It also smells more burnt then sweet. Old fluid is more murky than perfectly clear. ATF should look like cranberry juice, just thicker. Compare a drop of used fluid against new fluid on a white paper plate visually. Clean off the dipstick well before doing this so you're not seeing the deposits from the stick itself. The visual test can't tell you the status of the additives but it does give a sense of the fuild's health overall.
Generally speaking I've changed Dexron-III at 50k and VI around 75k. These are all transmissions with shift kits and performance clutch materials, and deep pans, but driven hard. I'd have to say a stock smooth-shifting trans will expire the fluid in fewer miles than what I am getting out of them realistically.
Get more opinions too; there is a lot of experience out there on this subject.