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Mixing ATF's to get a fill #4656905
02/05/18 01:19 PM
02/05/18 01:19 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
I have a 2003 Tahoe that is getting a reman'd Heavy Duty trans from Monster transmission. Their recommendation is Dexron VI, since Dexron III is no longer licensed by GM and is just a useless label anyone can throw on a red ATF-ish substance. I ordered 9qts. of AC Delco Dexron VI ATF from RockAuto because they are the only ones who don't require sacrifice of your life savings or first born child to purchase a case, all they had was 9qts. I think I am going to need another 3qts. I have read and it seems mixing ATF's is ok so long as you know your intended outcome. My other 3qts. I intend to be Napa/Valvoline full synthetic Dexron VI ATF. Could this cause issues? From my research on here, it seems AC Delco VI isn't a full synthetic, that is the basis behind my question. Is it ok to mix semi and full syn ATF? I'm fairly confident in the answer, but I'd like a little confirmation.
Thanks guys. It's not often I have oil related questions, but when I do I come here because you guys are an amazing pool of knowledge and scientific data.

Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656913
02/05/18 01:29 PM
02/05/18 01:29 PM
Joined: Aug 2003
Posts: 12,896
NE,Ohio
Rand Offline
Rand  Offline
Joined: Aug 2003
Posts: 12,896
NE,Ohio
just buy another gallon from amazon? same thing?

OTOH I would probably change out the fluid early on a "new" reman transmission

So not sure it matters much.

FYI they sell ac delco Dexron III(h) on amazon.

The dexron VI will be thinner.. probably not an issue on a fresh reman transmission.


2019 Jeep Cherokee Trailhawk 2.0T
Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656917
02/05/18 01:34 PM
02/05/18 01:34 PM
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Bottom_Feeder Offline
Bottom_Feeder  Offline
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
How much more was the NAPA Dex6 than the Amazon AC Delco Dex6 to make it not worth getting all of it at NAPA?

Also, you went expensive going with Monster for a transmission. Why go cheapest route for the fluid you're putting in it?

I find it hard to believe there are companies like Valvoline, Castrol, etc, putting out Dexron III fluids that are [censored] just because they are not held to a current licensed spec.

Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656919
02/05/18 01:35 PM
02/05/18 01:35 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
So the fun part of why I'm getting a new trans. I moved back in June, from KY to GA, 300 miles. On my trip I was towing a 6x12 U-Haul trailer chocked full o'goodies, heavy...well over the recommended weight by U-Haul. I was leaving KY at 6am, had to be here by 2pm for the walk-through of our rental. We got behind, I had read the owner's manual on towing(ps, I've pulled trailers my entire life, just wanted to make sure there is nothing special I needed to be doing). Being we were behind I laughed at the owner's manual, threw it back in the glovebox and boogied at 65-75mph, in overdrive, with 3.08:1 rear differential gearing, in a Tahoe, with a heavy trailer. Made the trip fine, the last 5 miles we hit traffic and I suppose the trans was hot and tired(I have a rather large auxillary tube and fin trans cooler mounted immediately behind the grille as well), 2nd slipped a little on me. Once unladen, the trans now slipped if over 2500rpm's in 2nd gear. I am not heartbroken, trans currently has 161k miles on it, and I feel it is ABSOLUTELY ridiculous that I cannot tow a 3,000+lbs. trailer at 70mph in overdrive with a full-size 1/2 ton SUV. Monster said I should have no problem accomplishing this with their HD trans. It's not that I do it very often, but if I need, I need to.

Re: Mixing ATF's to get a fill [Re: Bottom_Feeder] #4656926
02/05/18 01:41 PM
02/05/18 01:41 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
Originally Posted By: Bottom_Feeder
How much more was the NAPA Dex6 than the Amazon AC Delco Dex6 to make it not worth getting all of it at NAPA?

Also, you went expensive going with Monster for a transmission. Why go cheapest route for the fluid you're putting in it?

I find it hard to believe there are companies like Valvoline, Castrol, etc, putting out Dexron III fluids that are [censored] just because they are not held to a current licensed spec.

Monster is not "expensive." It was a nice compromise between price, capability, and quality. I really wanted to drop $3k on a performabuilt, but that's just overkill for my needs. It's the wife's DD kid toter, weekend vehicle, and road trips. It pulls a trailer 2-3 times a year, usually a golf cart trailer, this instance is a once every 2-3 year event. The demand for a premium quality fluid is not there. If I had realized the price difference between the 2 fluids before ordering I probably would've just gone with the Napa full-syn. Cost to return AC Delco at this point is prohibitive, run what you brung. On the first trans service, I will probably just use the full-syn Napa/Valvoline due to not having to deal with ordering, with a Wix filter...I love Wix filters. The price is $2/qt. The price wasn't the 100% motivation on buying the AC Delco. AC Delco, from what I know, is a pretty good fluid.
I concur on your last sentence. However, there's a lot of people who will do anything for a buck and the rebuilder recommends VI, also following recommendations keeps my warranty intact.

Last edited by 98dakota318; 02/05/18 01:49 PM.
Re: Mixing ATF's to get a fill [Re: Rand] #4656930
02/05/18 01:47 PM
02/05/18 01:47 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
Originally Posted By: Rand
just buy another gallon from amazon? same thing?

OTOH I would probably change out the fluid early on a "new" reman transmission

So not sure it matters much.

FYI they sell ac delco Dexron III(h) on amazon.

The dexron VI will be thinner.. probably not an issue on a fresh reman transmission.

Yes, I will probably perform F&F at 10-15k miles to check up on the new one to make sure it isn't in self-destruct mode.
Yes, the Dexron VI is thinner, but as you said, not a concern on a fresh reman, and it is the rebuilder's preferred ATF.

Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656931
02/05/18 01:47 PM
02/05/18 01:47 PM
Joined: Nov 2006
Posts: 19,910
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 19,910
MA, Mittelfranken.de
Really? New rebuilt unit and your fiddle fu... around playing home chemist? I am pretty sure no harm will come of it but I am not into chances like that with fluids that make paper/fiber friction disc grab or not. I wouldn't sleep good at night.
No offense but save the other stuff for something else.


ASE L1, Master. Deutsch Meisterbrief.
Re: Mixing ATF's to get a fill [Re: Trav] #4656933
02/05/18 01:51 PM
02/05/18 01:51 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
Originally Posted By: Trav
Really? New rebuilt unit and your fiddle fu... around playing home chemist? I am pretty sure no harm will come of it but I am not into chances like that with fluids that make paper/fiber friction disc grab or not. I wouldn't sleep good at night.
No offense but save the other stuff for something else.

I get what you're saying. However, they're both Dex VI which is a licensed product and has to meet a minimum specification. It's mainly the question of adding a little non-synthetic spec. fluid to full-syn spec. fluid.

Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656936
02/05/18 01:53 PM
02/05/18 01:53 PM
Joined: Dec 2011
Posts: 4,738
North Carolina
rooflessVW Offline
rooflessVW  Offline
Joined: Dec 2011
Posts: 4,738
North Carolina
All Dex VI is more or less the same. The only difference between the "full synthetic" stuff and anything else is the labeling.

I would personally just pick up a gallon of Delco Dex VI off of Amazon.


"Zed's dead baby, Zed's dead."
Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656947
02/05/18 02:01 PM
02/05/18 02:01 PM
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Bottom_Feeder Offline
Bottom_Feeder  Offline
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Isn't all Dexron VI supposed to be synthetic? Or am I thinking about brake fluid?

Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656951
02/05/18 02:06 PM
02/05/18 02:06 PM
Joined: Dec 2005
Posts: 9,891
Upper Midwest
kschachn Offline
kschachn  Offline
Joined: Dec 2005
Posts: 9,891
Upper Midwest
Originally Posted By: 98dakota318
So the fun part of why I'm getting a new trans. I moved back in June, from KY to GA, 300 miles. On my trip I was towing a 6x12 U-Haul trailer chocked full o'goodies, heavy...well over the recommended weight by U-Haul. I was leaving KY at 6am, had to be here by 2pm for the walk-through of our rental. We got behind, I had read the owner's manual on towing(ps, I've pulled trailers my entire life, just wanted to make sure there is nothing special I needed to be doing). Being we were behind I laughed at the owner's manual, threw it back in the glovebox and boogied at 65-75mph, in overdrive, with 3.08:1 rear differential gearing, in a Tahoe, with a heavy trailer. Made the trip fine, the last 5 miles we hit traffic and I suppose the trans was hot and tired(I have a rather large auxillary tube and fin trans cooler mounted immediately behind the grille as well), 2nd slipped a little on me. Once unladen, the trans now slipped if over 2500rpm's in 2nd gear. I am not heartbroken, trans currently has 161k miles on it, and I feel it is ABSOLUTELY ridiculous that I cannot tow a 3,000+lbs. trailer at 70mph in overdrive with a full-size 1/2 ton SUV. Monster said I should have no problem accomplishing this with their HD trans. It's not that I do it very often, but if I need, I need to.

Good job. Only 161,000 miles and you managed to do it in.


1994 BMW 530i, 228K
1996 Honda Accord, 263K
1999 Toyota Sienna, 400K
2000 Toyota ECHO, 271K
Re: Mixing ATF's to get a fill [Re: 98dakota318] #4656960
02/05/18 02:20 PM
02/05/18 02:20 PM
Joined: Mar 2016
Posts: 1,351
toronto
PeterPolyol Offline
PeterPolyol  Offline
Joined: Mar 2016
Posts: 1,351
toronto
Really? This much FUD over mixing differently branded same spec ATFs? LOL Wow.
Been there, done that (and 'much worse') and not in a low-risk beater app either. What are we scared about? Maybe the additives will clash, like the titans!!! Maybe the fluid viscosity will turn wildly unstable and 'not known'!? Maybe one day the tranny will find out it has two different brands of Dex VI in it, and take great offense!? Maybe it'll get the diabeetus!?!hide hide

Re: Mixing ATF's to get a fill [Re: kschachn] #4656967
02/05/18 02:26 PM
02/05/18 02:26 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
Originally Posted By: kschachn
Originally Posted By: 98dakota318
So the fun part of why I'm getting a new trans. I moved back in June, from KY to GA, 300 miles. On my trip I was towing a 6x12 U-Haul trailer chocked full o'goodies, heavy...well over the recommended weight by U-Haul. I was leaving KY at 6am, had to be here by 2pm for the walk-through of our rental. We got behind, I had read the owner's manual on towing(ps, I've pulled trailers my entire life, just wanted to make sure there is nothing special I needed to be doing). Being we were behind I laughed at the owner's manual, threw it back in the glovebox and boogied at 65-75mph, in overdrive, with 3.08:1 rear differential gearing, in a Tahoe, with a heavy trailer. Made the trip fine, the last 5 miles we hit traffic and I suppose the trans was hot and tired(I have a rather large auxillary tube and fin trans cooler mounted immediately behind the grille as well), 2nd slipped a little on me. Once unladen, the trans now slipped if over 2500rpm's in 2nd gear. I am not heartbroken, trans currently has 161k miles on it, and I feel it is ABSOLUTELY ridiculous that I cannot tow a 3,000+lbs. trailer at 70mph in overdrive with a full-size 1/2 ton SUV. Monster said I should have no problem accomplishing this with their HD trans. It's not that I do it very often, but if I need, I need to.

Good job. Only 161,000 miles and you managed to do it in.

Lived longer than some babied and well maintained examples of the 4L60E lol. It still works perfect, as long as you stay below 2500rpm's in second gear lol. I don't mind taking risks, if it wasn't used to haul my kids and take road trips I'd rock this sucker with some Lucas Trans Fix until it had nothing left. Ever dealt with a stranded wife? Not something you do twice and live.

Re: Mixing ATF's to get a fill [Re: PeterPolyol] #4656971
02/05/18 02:30 PM
02/05/18 02:30 PM
Joined: Dec 2010
Posts: 12
Georgia
98dakota318 Offline OP
98dakota318  Offline OP
Joined: Dec 2010
Posts: 12
Georgia
Originally Posted By: PeterPolyol
Really? This much FUD over mixing differently branded same spec ATFs? LOL Wow.
Been there, done that (and 'much worse') and not in a low-risk beater app either. What are we scared about? Maybe the additives will clash, like the titans!!! Maybe the fluid viscosity will turn wildly unstable and 'not known'!? Maybe one day the tranny will find out it has two different brands of Dex VI in it, and take great offense!? Maybe it'll get the diabeetus!?!hide hide

This is my thinking. It's all the same additive packages.

Re: Mixing ATF's to get a fill [Re: 98dakota318] #4657034
02/05/18 03:17 PM
02/05/18 03:17 PM
Joined: Jan 2018
Posts: 38
Eastern Seaboard
Collingwood Offline
Collingwood  Offline
Joined: Jan 2018
Posts: 38
Eastern Seaboard
So, Dexron 6 mixes with and works fine with Dex3 applications?

The Dex6 costs about twice as much as D3/M fluid.

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