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XG is the correct code for the GM 5L40-E transmission used in the L322. The G before this code simply means it’s a 5L40-E, the letter Z would mean it’s a 5L50-E.
The number above the G is the year of manufacture e.g. 3 = 2003
The GM box uses Dexron fluid. The original spec. for the 5L40-E in the L322 was a Dexron III fluid called Texaco Texamatic 7045E.
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I assume that it’s no longer possible to source this fluid because the Dexron III licences expired in 2006 and GM moved users onto Dexron VI. A potential issue, though, with using Dexron VI is that its viscosity (new) is lower than that of Dexron III. Not necessarily a good thing if your valve blocks are worn, which is a particularly common issue with the 5L40-E! The justification is that the better shear stability of Dexron VI means the viscosity remains at its design specification for longer i.e. after a period of use it will be higher than ‘worn out’ Dexron III.
Someone on another forum asked if I thought a fluid called Texaco ATF HD 389 might be a more suitable alternative than Dexron VI. It has a kinematic viscosity of 7.1 mm²/s at 100⁰C and 34.9 mm²/s at 40⁰C. This compares to 7.4 & 33.8 for the original Texamatic 7045E fluid and 5.8 & 29.5 for Dexron VI so, on the face of it, it would seem a more suitable replacement for Dexron III than Dexron VI.
Phil
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18th Jun 2024 8:58pm
