DEXIII or DEXVI in higher mileage 4l60e

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Hello everyone, Im new here on BITOG and have a question about which fluid to run in my 1997 4l60e transmission. I know the factory fill was a DEX3, but Ive been thinking about switching over to a DEX6 or similar synthetic fluid (Mobil 1). The Truck has 160,000 miles on it, and i did a fluid and filter change on it about three years ago with Castrol dex/merc fluid. Ive been searching around here the last few hours and found plenty of info, I just cant seem to make up my mind. Ive read that the DEX6 is a lighter viscosity oil than the DEX3. Ive also read that Mobil 1 syn. is closer in viscosity to DEX3. I would think that i want to stay as close to the viscosity of a dex3 as i can because that's what the truck is used to. Ive also stumbled upon people recommending the use of Valvoline Maxlife ATF in an older transmission like mine. I just dont want to change to synthetic or DEX6 fluid and have the trans go south. Please someone steer me in the right direction.

Should i make the switch or should I stay with good old dex/merc?

What fluid does everyone recommend i use?
Thanks

-Kyle
 
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Well since Dex3 isn't supported and/or licensed then I would go with an inexpensive Dex 6. With the mileage a pan drop and refill with a Supertech Dex6 for example should be excellent. I did this over the summer to my friend's 95 Delta88 and it didn't have any issues with the lighter fluid. His transmission shifts great!. The Supertech should be at least a blend and I think this would be an excellent choice.

All of the FWD W-body guys seem to have had good luck with Dex6 in the 4T65. Many of them being around 100k. The Olds I mentioned had 100k on it.
 
Kyle
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The proper fluid to use here is DEXRON VI which replaces the no longer licensed DEXRON III. You are correct, Dexron VI is indeed lighter to start with than the Dexron III. But remember that the Dexron VI is more shear resistant than the old stuff. The dex III will shear to or below what the Dexron VI starts out life as, and the Dexron VI maintains its virgin viscosity for much much longer.

I have personally used Dex VI in many Dex III spec'd transmissions and can say that every one of them shifted a lot better and the fluid has held up quite well in contrast to the Dex III. To get the full effect, do a cooler line flush to get the most Dex VI in there. Good luck!
 
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Thanks for the advice guys, What do you think of Valvoline dex6 in my application? Would a full synthetic be preferred? or is there a reason to stick with the semi-synthetic DEX6's? Also just thought id add that ill be installing a deep pan that holds an extra quart of fluid and also has a drain plug
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You can use any DexronVI.
Or, if you're on a budget, you can use and Dex/Merc equivalent.
And, Mercon-V would be an upgrade to the Dex/Merc and cheaper than DexronVI.

If you use the DexronVI, just stick with a name brand fluid and don't worry about whether its synthetic, blend, or not.

At 160k, the trans can go south if you sneeze. So, pick a fluid, keep driving, and don't worry about it.
 
So after some more reading I think Ive narrowed my decision down to either Valvoline Max life dex/merc Or Valvoline DEX6. Any opinions? I know some of you have to be running 4l60e's.
Sorry if this is a newbie type of question/Thread BTW.
 
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I have Valvoline Dex6 full syn in the Regal and M1 Dex3 was before that. Between the two the largest difference is downshifts under hard acceleration. The Dex6 is alittle faster/snappier.
 
we have a fleet that includes 5.3 Silverados with the 4L65-E, a slightly upgraded version of your trans.

We switched EVERYTHING GM to Dex VI. It is a noticeably superior trans fluid for almost anyone, a very tough spec to meet.

I use the Valvoline as it is full synth, but any brand will be a terrific upgrade for you.
 
Here's a question that I thought would be relevant... if just doing a pan drop and only replacing 5 quarts or so, is it still worth it to replace w/ dex VI? will it run nicely with the old dex/ merc that's in there? asking because I have a 4l60e too.
 
I did just that. Replaced my pan and put dex VI in. Felt nice, though there is some shift characteristics that have changed which I cannot place... For GM ATs, Id do it. For other makers ATs that spec dex III, Im not as sure.
 
Originally Posted By: JHZR2
I did just that. Replaced my pan and put dex VI in. Felt nice, though there is some shift characteristics that have changed which I cannot place... For GM ATs, Id do it. For other makers ATs that spec dex III, Im not as sure.


This is exactly what im afraid of... Even with the miles this tranny has it still shifts nice and firm. I dont want to change to DEXVI and have it shift any different. Most threads ive read state that it changes shift characteristics (softer shift) but yet everyone recommends it...
 
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