Mixing ATF's to get a fill

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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.
 
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.
 
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.
 
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.
 
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:
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.
 
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.
 
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.
 
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.
 
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.
 
Really? This much FUD over mixing differently branded same spec ATFs?
lol.gif
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!?!
27.gif
27.gif
 
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.
 
Originally Posted By: PeterPolyol
Really? This much FUD over mixing differently branded same spec ATFs?
lol.gif
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!?!
27.gif
27.gif


This is my thinking. It's all the same additive packages.
 
Originally Posted By: 98dakota318
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.

These tranny’s aren’t as bad as people make them out to be. Mine is 20 years old has close to 146k and isn’t babied. Towed a race car by the previous owner and I tow with it as well. Original trans.
For your topic the Napa stuff will be just fine. When you change it at 15k like you said just buy all one brand then.
 
Originally Posted By: 98dakota318
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.


Sorry I misread your post I thought one was Dex III. Dex VI from A and Dex VI from B mixed makes no difference.
 
Originally Posted By: ChevyBadger

These tranny’s aren’t as bad as people make them out to be. Mine is 20 years old has close to 146k and isn’t babied. Towed a race car by the previous owner and I tow with it as well. Original trans.
For your topic the Napa stuff will be just fine. When you change it at 15k like you said just buy all one brand then.

I agree, the 4L60E is a pretty good transmission, they have had their fair share of failures. A shift improver kit and a Sonnax Sure Cure kit will go a LONG way in making a 4L60E live a long and prosper life, along with regular maintenance.
I have seen many 4L60's live well past 200k miles being used hard and poorly maintained at best. I have seen many 4L60's that have never towed or hauled a thing, maintained by the book, and never make it close to 200k(my transmission, previous owner never towed or hauled anything and maintained it well). It's like the more they are used and abused the longer they live. Back in my GM Tech days people would come in with a 4L60E equipped vehicle that had 150k miles and never had a trans service, wanting the first trans service. I always told them that in my opinion, if you haven't serviced a 4L60E by 100k miles, don't service it ever. It seemed that once they crossed that 100-125k mile threshold without a trans service, if you serviced it, it was only a matter of months until it failed. Leave it be, they tended to have many many more miles in them unserviced, with the old nasty fluid in them. I understand it makes no sense, but theory is quite different from application many times.
 
I thought it was supposed to be. I haven't read the in depths on it. I ran across a thread on here that someone was talking about different manufacturer's of DexVI, they had a confirmed full-syn list, and a unconfirmed full-syn list. The AC Delco was not on the confirmed list.
 
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