4l60e which fluid? heard bad about synthetics

[apollo18]

hey guys! have a 2003 4l60e in my hummer h2. it has 240,000 km on it on the original transmission. i dont remember the maintenance history for the tranny between 2003-2015 i have no clue but i know around 2015-2016 ish? my mexchanic did a pan drop and put in some fresh fluid but i dont know if it was dexron iii or dexron 6. so now i want to switch out the fluid all 16 quarts or whatever thru the coolers lines but dont know what fluid to use. ive heard the saying that you should never switch to synthetics later on because it leaks, but i also read the 4l60 doesnt like synthetic as it is too slippery. i was reading on the ls1 tech forum and all the tranny builders say to stick with conventional dex 3. so for the pan drop my mechanic did 4-5 years ago i have no clue what fluid he used for the 5-6 quarts, it could have been dex 3 or dex 6 no clue. 

 

so i want to run conventional dex 3 which seems easy to find as theres so many dex/merc fluids, but my problem is that i have read that dexron 6 is a synthetic and if my truck has dexron 6 synthetic in it, then i dont want to cause a problem by switching from dex 6 to dex 3. i dont know what fluid the truck has in it, it could be dex 6 fully or it could be a mix of both, or it could be all dex 3.

 

 

so all im trying to ask is if there is any possibility for something to go wrong if my tranny had synthetic dex 6 in it and i run conventional dex 3 now. the truck was originally recommended to use dex 3 when it was released but i always hear how people say not to use synthetics later in life because it ends up blowing thru seals/leaking so i dont want something to happen like that if i switch to conventional dex 3

 

 

thanks!

 

[davester]

I would put a DexIII fluid in it, as I was told on another forum that, while Dex VI is supposed to be a replacement for DexIII, not all seals used prior to DexVI being developed work well with it, and so it may leak when switched to DexVI.

 

I believe both DexIII (at least the later versions/revisions of it) and DexVI are synthetic.

[Jsdirt]

Dex 6 is backwards compatible, but, I would run what the factory fill was at the time. I don't trust these new formulations to protect the way the old stuff did. These days auto manufacturers don't give a crap about longevity, and put fuel mileage and emissions above all else - so with that in mind, I, personally, steer clear of the new formulations in older equipment.

[Black02Silverado]

You can go back to dexron III with no issues.  It is my understanding it has been discontinued so not sure where you can get it.  I have not looked for it.  The closest to dexron III that I know of is AMSOIL's ATF.

 

I switched my 2002 silverado over to dexron VI at 100,000 with no issues.  But then I did switch it over to synthetic dexron III, AMSOIL's ATF back when I purchased it with less than 10k on it at the time. Then I did a pan drop at 70k again with AMSOIL's ATF which is dexron III,  so at or around 100,000 miles I did a complete exchange out of the dexron III and used AMSOIL's dexron VI.  No issues at all and the UOA I sent off came back great. I even tow a 4klbs trailer monthly.

 

So I would think all would be fine with moving up to a complete exchange of dexron VI. 

 

 

[Jsdirt]

Good to know. Thanks, Nick. 

[txab]

Over 100k on Dex VI in a 4L60E. No issues whatsoever. We've still got GMT800 trucks in our fleet that have Dex VI or Amsoil for fill, also with no issues

[apollo18]

just wanted to ad! i called my dealerships and i found out that i had a full fluid exchange done 100,000 km ago and they put in dex 6, so that means the 4l60e is running fully or primarily dex 6.

 

so should i stay with dex 6 then? since its lasted the last 100,000 km perfectly fine on dex 6. current tranny km is at 245,000km

 

or its all good if i just find a dex/merc fluid that is suitable for gm dexron iii. since the license for dex 3 expired, i found a couple conventional fluids i was thinking of running..

https://www.peaveymart.com/Multi-Purpose-ATF-Fluid-757L-P25935.aspx

which is a dex/merc fluid

https://www.canadiantire.ca/en/pdp/motomaster-dexron-iii-mercon-automatic-transmission-fluid-0281502p.html

or this which is "for vehicles that require dex 3"

 

i think valvoline even makes a fluid for dex 3 still/castrol so i could do that too!

 

i heard all dex 3 fluids are the same, so do i just go with what i can find the cheapest?

 

the people over at the ls1 tranny forum recommend conventional dex 3 but i have a dillemna now, since the truck has been on dex 6 for the last 100,000 km then it seems like i should follow "dont fix what aint broken" and just go with delco dex 6

but alot of people swear by keeping it at conventional dex 3

 

 

sorry for beating a dead horse, just wanted to include the info that now i know it has dex 6 running in it for the last 100k km and now i dont know which way to go

[Black02Silverado]

Go with the dexron VI.  You already have it in there and being a somewhat synthetic it will protect against heat way better than dexron III ever could.  No need to overthink this.   Stick with what has been working fine and your transmission will thank you.

[txab]

Don't go backwards now