Pick my ATF

Which ATF?


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Morrow Mountain
1990 GMC Sierra SL1500. THM400 3-speed. OEM fluid is obsolete, so help me pick something from modern offerings. Current fluid looks nasty gray and gives off slight burnt smell. 133k miles, so could be factory fill...
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Couldn't find any info on ATF capacity. Different forums claim 4-8 quarts. Many Corvette guys claim that TH400 shifts better with JD Hy-Gard or UTF. Anyone can confirm or bust this myth? I do plan to install the biggest transmission fluid cooler I can find in near future.
 
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If your transmission doesn't have a drain plug, get an aftermarket pan that has one :)

Maxlife is good stuff and the best value for a synthetic ATF.

Castrol Full Synthetic ATF is also a good choice when it is on sale. It is also licensed Dexron VI, if that matters.

Redline D4 and D6 are good, but they cost a lot more.
 
How about an other option?

The is my recommendation for your 1990 GMC 1/2 ton pickup:
LIQUI MOLY 20022 Top Tec ATF 1200- RockAuto sells this is a 20 liter jug. Fully synthetic, made in Germany, and listed as compatible with your GMC. I run this trans fluid in my 2002 F350 V10 gasser.
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If it's a beater you're just performing maintenance on to get a little more out of it, any Dex/Merc will do, If it's a vehicle you love and you're keeping it in pristine condition, do a cooler line flush with TES295.
 
I’ve used Supertech HM DexMerc in my 4L60E for years and it still shifts like butta at 230,000 miles! A friend ran a TH400 in a late 70’s work van over a half million miles and never changed the fluid! Just occasional top offs every year or two. The old TH400’s are one of the best automatic transmissions ever built! (y)
 
How about an other option?

The is my recommendation for your 1990 GMC 1/2 ton pickup:
LIQUI MOLY 20022 Top Tec ATF 1200- RockAuto sells this is a 20 liter jug. Fully synthetic, made in Germany, and listed as compatible with your GMC. I run this trans fluid in my 2002 F350 V10 gasser.
View attachment 106577
What does being made in Germany get you?
 
Likely a fully synthetic fluid that meets the full definition.

Kind of like extra virgin olive oil. In Europe, if one purchases evoo, you know exactly what you are buying. In the USA, purchase evoo and the standard is sometimes significantly less.
 
Likely a fully synthetic fluid that meets the full definition.

Kind of like extra virgin olive oil. In Europe, if one purchases evoo, you know exactly what you are buying. In the USA, purchase evoo and the standard is sometimes significantly less.
It says it's based off of Hydro-cracked synthetics. It says it in the 2016 version, but not in the 2022 version, but they have the same pour point.

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