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Transmission Fluid Change Question

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22K views 17 replies 6 participants last post by  Pirate1 
#1 ·
Ok. So its time for me to drop the transmission pan and change the filter and fluid. The owners manual says Dextron III transmission fluid. What i would like to do is put Mobil 1 Full Synthetic ATF to fill it up (5 quarts or so). But the thing that I am wondering about is the "Dextron III fluid" is that full synthetic formula? the reason i ask is i heard that your not supposed to mix conventional and synthetic ATF fluids? is that true? Either way is the Dextron III fluid a synthetic or not? I am wondering if this is wise to do. Thanks.
 
#5 · (Edited)
I did a little research online and I found the answer. The answer is that conventional and synthetic fluids ARE 100% compatible with each other. This includes Automatic Transmission Fluid. It says so right on the Valvoline website (even tho i'm not a big fan of valvoline). Thats where i was able to find it. Here Is The Q&A:

Is it ok to mix synthetic ATF with a conventional and/or synthetic blend ATF?

Yes. Synthetic and conventional fluids are 100% compatible to each other.

the link for that is here: (its question number 5) http://www.valvoline.com/faqs/system-fluids/automatic-transmission-fluid/

Now we can both change to mobil 1 ATF without worrying about if it is good or not to mix the two. :) :woohoo:
 
#6 · (Edited)
I also found on the Mobil 1 website proof to back this up. It says this (look especially at the RED):

Mobil 1 Synthetic ATF combines high-performance synthetic hydrocarbon base oils and a superior balanced additive system to provide significantly higher levels of performance above conventional fluids. This unique, advanced technology provides long drain capability, excellent friction retention, and low-temperature fluidity. Further, it helps to improve overall transmission durability and cleanliness.
Mobil 1 Synthetic ATF is also compatible with conventional ATFs.
The link for that is here if you want to take a look: https://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_1_Synthetic_ATF.aspx
Now we can be sure that mixing ATF fluids is a safe thing to do :thumbsup: :woot:
 
#7 ·
I also found on the Mobil 1 website proof to back this up. It says this (look especially at the RED):

Mobil 1 Synthetic ATF combines high-performance synthetic hydrocarbon base oils and a superior balanced additive system to provide significantly higher levels of performance above conventional fluids. This unique, advanced technology provides long drain capability, excellent friction retention, and low-temperature fluidity. Further, it helps to improve overall transmission durability and cleanliness.
Mobil 1 Synthetic ATF is also compatible with conventional ATFs.
The link for that is here if you want to take a look: https://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_1_Synthetic_ATF.aspx
Now we can be sure that mixing ATF fluids is a safe thing to do :thumbsup: :woot:
:D:thxThank you so much as I had already bought my fluid!:thumbsup:
 
#3 ·
If you are really keen to get more fluid out and have a garage to do the fluid change in.....

You will need an inch/pound torque wrench to do this properly

Once you have the pan and filter off loosen off all the valve body bolts - no more than 3 turns then let the transmission drip overnight. This will allow more fluid to bleed out of the torque converter. The valve body should drop and hang on the bolts. If it doesn't don't pry or pull on it!

Then snug the bolts using a nut driver starting in the middle and work outwards.

Then torque the bolts to 100 to 110 INCH POUNDS starting in the center working outwards.

Dexron 3 is fine for all transmission 2005 and earlier. GM upgraded the fluid spec to dexron 6 for the 6 speed transmissions and then applied it to all other GM transmission dating back to '49.
 
#10 ·
When i changed the fluid on mine i dropped the pan, let drain, take out filter, replace with new filter, cleaned out the pan with brake parts cleaner, dried the pan, put the pan back together, dumped in 4 quarts of Mobil 1 Fully Synthetic ATF: https://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_1_Synthetic_ATF.aspx drove it for a little bit, checked the level. Showed it was a little low. added a fifth quart, drove it for 15 mins, checked the fluid again. Then it was perfect. Have been driving it for over a week & it actually shifts a little easier in my opinion. No slipping or anything abnormal at all.
In my opinion just by adding dex 6 fluid with dex 3 fluid should not cause the tranny to slip. Is it slipping Bad? I know with several GM vehicles that the trannys go slip from time to time, i have noticed this with the gmc savannas and the chevy silverados. It only slips occasionally and not bad. The mechanics call this a glitch.
On the Mobil 1 website it gives the following:
Also suitable for use in vehicles that specify the following fluid requirements:
All 2005 and earlier GM vehicles**
** Mobil DEXRON-VI ATF is recommended for 2006 and newer GM vehicles and improved performance in 2005 and earlier vehicles, wherever DEXRON is specified.
https://www.mobiloil.com/USA-English/MotorOil/Other_Products/Mobil_1_Synthetic_ATF.aspx
So with that being said in my opinion i don't think that the fluid addition would cause a problem. But maybe if the fluid is extremely dirty and adding dex 6 would cause it to slip?? hard to tell. There are many people who are on this site that would probably give more answers to the solution.
Hope all goes well for you.
 
#9 ·
Gee man, I hate to hear that! My owners manual says III and I have an 06 manual that came with truck and it says VI, and from what I've learned from this site VI is the preferred fluid and that's what I just changed mine out with:worried:No slippage yet, but now I'm concerned! Please keep us posted. Did you by any chance change your filter? I did! Good luck friend:grouphug:
 
#14 ·
Transmission shifts good and smooth, really can tell the difference in throttle response! As for the manual, they are basically the same with only a few small differences, but I just wanted an original manual. Our truck was a fleet truck from an Insurance company and they took pretty decent care of it and that is amazing in and of itself! My only concern was that when we changed the transfer case fluid it appeared to be plain old gear oil, but not now as I put smurf oil in it!
 
#18 ·
2007 Envoy 4.2L Transmission Fluid

Hello All, I have a 2007 Envoy that came with a 2006 manual when I bought the truck. Now I am getting ready to replace the transmission fluid / filter and would like to know what the correct recommended transmission fluid for my 2007 is? Thank you in advance!!
 
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